WO2024263754A1

WO2024263754A1 - Systems, apparatus, and methods for dilution and effective mixing of high viscosity long-term fire retardant liquid concentrates

Info

Publication number: WO2024263754A1
Application number: PCT/US2024/034786
Authority: WO
Inventors: Joseph Mclellan; Michael White
Original assignee: Frs Group, Llc
Priority date: 2023-06-20
Filing date: 2024-06-20
Publication date: 2024-12-26

Abstract

Systems and methods for automatedly providing ready -to-use (RTU) fire retardant product are provided. A liquid concentrate (LC) fire retardant is mixed with water to form a fire retardant compound. An LC head pressure of the LC fire retardant changes while the LC fire retardant and water are mixed, and an in-line refractive index of the RTU fire retardant product is automatically and repeatedly measured. At least one flow variable is adjusted or maintained during the mixing process in order to achieve a target refractive index of the RTU fire retardant product.

Description

Attorney Docket No. FFRS-012WO01 SYSTEMS, APPARATUS, AND METHODS FOR DILUTION AND EFFECTIVE MIXING OF HIGH VISCOSITY LONG-TERM FIRE RETARDANT LIQUID CONCENTRATES CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority, under 35 U.S.C. § 119(e), to U.S. Provisional Patent Application No. 63/509,087, filed June 20, 2023 and entitled “Systems, Apparatus, and Methods for Dilution and Effective Mixing of High Viscosity Long-Term Fire Retardant Liquid Concentrates,” which is incorporated herein by reference in its entirety. BACKGROUND Long-term fire retardants contain retardant salts that decrease fire intensity and slow the advance of a forest fire. Such fire retardants conventionally are available as dry powders or liquid concentrates (LCs) that are mixed with water, wherein the resulting “ready-to-use” (RTU) mixture improves the effectiveness and ability of water to cling to fuels. The U.S. Department of Agriculture Forest Service Specification 5100-304d provides specifications of long-term fire retardants for wildland firefighting in the United States (these specifications also have been adopted in some other countries). As noted above, long-term fire retardants conventionally are prepared at centralized manufacturing facilities to form dry powders or liquid concentrates (LCs). These dry powders or LCs are then shipped to deployment areas, such as airtanker bases that support aerial fire management operations. At such bases, the dry powder or LC fire retardants are mixed with water to form a ready-to-use (RTU) fire retardant product, which is then loaded onto various types of aircraft that are deployed to drop the RTU product on or near fires. Examples of various aircraft employed to drop fire retardant on fires include a Single Engine Air Tanker (SEAT) with a retardant capacity of 800 gallons or less, a Large Air Tanker (LAT) with a retardant capacity of up to 8000 gallons (e.g., 2000-4000 gallons), and a Very Large Air Tanker (VLAT) with a retardant capacity of over 8000 gallons. The U.S. National Wildfire Coordinating Group (NWCG) has published an interagency guide regarding the planning and setup of fire retardant air bases (Interagency Retardant Base Planning Guide February 2006), as well as standards for airtanker base operations (NWCG Standards for Airtanker Base Operations, PMS 508 June 2022). Attorney Docket No. FFRS-012WO01 At a given retardant airtanker base, a “mix master” is a qualified individual who mixes dry powders or LCs with water at specified ratios to prepare ready-to-use (RTU) fire retardant product to be loaded onto an airtanker. The mix master works in a retardant “mix plant” constructed in an airtanker loading area (or “pit”) at the airtanker base that includes various equipment to facilitate mixing of dry powders or LCs with water. FIG.1 illustrates respective elements of a conventional LC mix plant at an airtanker base. As illustrated in FIG.1, particularly with respect to liquid concentrate (LC) fire retardants, a conventional LC mix plant includes at least one tank containing the LC fire retardant. Some examples of conventional LC fire retardants that would be diluted and blended in the conventional LC mix plant shown in FIG.1 include the PHOS-CHeK^® LC95 series and LCE20-FX liquid concentrates, having viscosities in a range of from about 100 to 400 centipoise (cP). The conventional LC mix plant shown in FIG.1 also includes a water tank and a manually-operated proportioning valve to blend the LC fire retardant with water according to specified mix-ratios and thereby create ready-to-use (RTU) fire retardant product (“mix”). The conventional LC mix plant may also include a gas-powered loading pump to load the RTU fire retardant product onto an airtanker, as well as various plumbing (e.g., four-inch diameter pipes or hoses) to interconnect the LC container(s), solvent tank, manually-operated proportioning valve, and loading pump. As would be appreciated by one of ordinary skill in the art, a conventional LC mix plant of this type does not require any electrical power for operation. As illustrated in FIG.1, at the output of the loading pump, a flow meter is required to detect a flow rate (e.g., gallons/minute) and density (or specific gravity) of the RTU fire retardant product as it is being loaded onto the airtanker. The U.S. Department of Agriculture Forest Service requires that a mass flow meter must be utilized for all aircraft loading applications “to ensure that safe aircraft load limits are not exceeded, to help optimize payloads, and to ensure that just compensation is paid to retardant contractors.” (Interagency Retardant Base Planning Guide February 2006, page 40). Mass flow meters must be installed in the loading lines in such a way that each plane load of RTU product is quantified and product density is monitored. A target retardant delivery rate for a Large Air Tanker (LAT) is 400 to 500 gallons per minute and for a Single Engine Air Tanker (SEAT) it is 200 to 300 gallons per minute. (Interagency Retardant Base Planning Guide February 2006, page 35). One example of a conventional flow meter includes a Micro-Motion^® flow meter, which Attorney Docket No. FFRS-012WO01 utilizes Coriolis flow tubes vibrating in opposition to one another when fluid is flowing through the tubes and a drive coil is energized to cause the tubes to oscillate. As would be appreciated by one of ordinary skill familiar with airtanker base operations, given the requirements specified in the Interagency Retardant Base Planning Guide February 2006, the flow meter is typically the last component in the path of RTU fire retardant product flow prior to an airtanker’s supply tank. Regarding quality control of the RTU fire retardant product, as also shown in FIG.1, a sampling valve located after the manually-operated proportioning valve and before the gas- powered loading pump is employed to permit sampling of a small amount of RTU product for analysis using a hand-held refractometer. Such a hand-held refractometer conventionally is used periodically at retardant airtanker bases to determine the amount of retardant salt in a sample of RTU fire retardant product. The concentration of retardant salt in the RTU product determines the density (mass per unit volume) of the RTU product, which in turn determines the refractive index (ability to bend light) of the RTU product – a refractometer is employed to measure this refractive index, which in turn is correlated to salt content and density. Knowing the density (or specific gravity) of the RTU product is important in determining the weight of an airtanker after it has been loaded with the RTU product. Pursuant to section 4.3.2 of the U.S. Department of Agriculture Forest Service Specification 5100-304d, “the refractometer reading of a properly mixed retardant shall be determined using a hand-held refractometer that the arbitrary scale found in industrial fluid testers or the Brix scale when needed” (as would be readily appreciated by those of skill in the art, the arbitrary scale found in industrial fluid testers is known as the 10440 VP arbitrary scale). Accordingly, as shown in FIG.1, a mix master (or other authorized pit personnel at the retardant airtanker base) conventionally uses a hand-held refractometer to measure the refractive index of the RTU product, which as noted above correlates to the concentration of retardant salt in the RTU product. To this end, the mix master applies a small sample of RTU product to a prism of the refractometer and then holds the refractometer to a light source to take a reading. Such manual measurements of refractive index of the RTU product are typically done once or more per each aircraft load. Attorney Docket No. FFRS-012WO01 SUMMARY The Inventors have recognized and appreciated that there are multiple shortcomings with conventional fire retardant mixing operations, particularly with respect to liquid concentrate (LC) fire retardants. First, mixing of LC fire retardants with water generally is a time-consuming process, which is a problem in firefighting where time is of the essence (e.g., it can take 20 minutes or more to adequately mix an LC with water to form the RTU product for application to a fire). Accordingly, the time it takes to dilute and mix LC fire retardant with water to make ready-to-use (RTU) fire retardant product may limit how quickly a forest fire can be quelled. Another problem with conventional LC mixing operations includes quality control and variability between batches (e.g., variations over time in concentration and/or homogeneity of the RTU product), which can adversely affect the ability to effectively control fires. The Inventors have further recognized and appreciated that the foregoing and additional challenges arise if a relatively higher viscosity liquid concentrate (LC) fire retardant is used to prepare an RTU fire retardant product. The U.S. Department of Agriculture Forest Service Specification 5100-304d, defines viscosity ranges for mixed RTU fire retardant products in Section 1.2.5 as follows: 1 1 0

Although the viscosity categorizations in the above chart are applied to mixed RTU fire retardant products, they may also be applied to LCs for purposes of comparison and illustration. In particular, the Inventors have considered the use of LCs having a viscosity above the “High Viscosity” range indicated in the above chart (e.g., LCs in the range of from about 1500 cp to 3000 cp, hereafter referred to as “ultra-high” viscosity) for missing with water to prepare RTU fire retardant products (by comparison, the PHOS-CHeK^® LC95 series and LCE20-FX liquid concentrates noted above in the BACKGROUND section have Attorney Docket No. FFRS-012WO01 viscosities in a range of from about 100 to 400 cP, which falls into the “Low viscosity” range indicated in the above chart). Regarding the use of “ultra-high” viscosity LCs as contemplated by the Inventors, some examples of such “ultra-high” viscosity LC fire retardants include, but are not limited to, magnesium chloride (MgCl) salt-containing LCs such as those disclosed in U.S. Patent No.10,960,249, issued March 30, 2021, entitled “Long-term Fire Retardant With Corrosion Inhibitors and Methods for Making and Using Same”, which patent is hereby incorporated herein by reference. It should be appreciated that other LCs such as those disclosed in one or more of the following U.S. patents, patent publications, or patent applications, each of which is hereby incorporated herein by reference, are also contemplated by the Inventors for use in connection with the inventive concepts disclosed herein: A e R F 0 F 0 F 0 F 0 F 0 F 0

LC fire retardants having ultra-high viscosity in the range of from about 1500 cP to 3000 cP present particular challenges in the preparation of RTU fire retardant products, based at least in part on the effect that a significantly higher viscosity has on the flow rate of the LC fire retardant. Attorney Docket No. FFRS-012WO01 More specifically, as would be readily appreciated by those of skill in the art, the Poiseuille Law of fluid dynamics provides a relationship between the viscosity of a fluid (i.e., an incompressible Newtonian fluid in laminar flow), a length of cylindrical pipe of constant circular cross-section through which the fluid flows and the pressure drop due to the viscosity of the fluid, as follows:

proportional to flow rate. It is also understood that Poiseuille’s Law does not apply in the limit of very low viscosity and wide and/or short pipe (e.g., low viscosity or a wide pipe may result in turbulent flow, requiring a more complex relationship; however, even when turbulence is a factor, Poiseuille's Law provides a reasonable approximation of the how flow rate changes with viscosity of the fluid and pipe radius). With reference again to FIG.1, conventional LC mix plants may include a loading pump, downstream of a manually-operated proportioning valve, to pump RTU fire retardant product into an airtanker. The manually-operated proportioning valve in turn is coupled via pipes to an LC container and a solvent tank respectively. A pressure (or suction) provided by the gas-powered loading pump is exerted on both the water and the LC to draw these constituents through the pipes and the manually-operated proportioning valve so as to create the RTU product. Attorney Docket No. FFRS-012WO01 In particular, a first pressure exerted by the water in the solvent tank (referred to herein as “water head pressure”) and a second pressure (or suction) exerted by the pump provide the pressure difference in Poiseuille’s Law shown above that in turn affects the volume flowrate of water in the mix plant. Similarly, a third pressure exerted by the LC in the LC container (referred to herein as “LC head pressure”) and the second pressure (or suction) exerted by the pump provide the pressure difference that in turn affects the volume flowrate of LC in the mix plant. For relatively lower viscosity LCs (e.g., the PHOS-CHeK^® LC95 series and LCE20-FX liquid concentrates), the action of the pump on both the water and the LC results in sufficiently similar respective flow rates of the LC and the water (given similar or identical length and radius of respective pipes used to carry the water and the LC). Under these conditions of relatively similar viscosity constituents, a particular mix ratio of the LC and water may be effectively achieved to create the RTU product by manual operation of the proportioning valve. In particular, the manually-operated proportioning valve generally is positioned by a mix master to vary a first aperture size within the valve for the water and a second aperture size within the valve for the LC fire retardant (which essentially changes the radius in Poiseuille’s Law above for each of the LC and the water). The varied aperture sizes in turn adjust the respective flow rates of the constituents as they mix in the valve so as to achieve the specified mix-ratio for the RTU product. Thus, a ratio of the aperture size for the water and the aperture size for the LC within the valve generally correlates to a specified mix-ratio for the RTU fire retardant product. However, the Inventors have recognized and appreciated that for ultra-high viscosity LC fire retardants (e.g., magnesium chloride salt-containing LCs having viscosities in the range of 1500 cp to 3000 cp), it is significantly more challenging to achieve specified mix- ratios to create an RTU fire retardant product using a conventional manually-operated proportioning valve. More specifically, with reference again to Poiseuille’s Law illustrated above, the significantly different viscosities between an ultra-high viscosity LC fire retardant and water would result in significantly different respective flow rates of LC fire retardant and water entering into the proportioning valve – this would be the case assuming identical or similar pipe radius and length (e.g., consider the difference between drinking a thick milk shake and a glass of milk using identical straws) and similar pressure differences for both the LC and the water (created by the loading pump and assuming similar head pressures of the LC and the water). This prospective difference in respective flow rates under these disparate-viscosity Attorney Docket No. FFRS-012WO01 conditions is further complicated by recognizing that the assumption of similar head pressures does not apply; in particular, given the ultra-high viscosity of the LC fire retardant, the head pressure of the LC in the LC container and the head pressure of the water in the solvent tank may be significantly different. These circumstances are complicated yet further by a constantly changing head pressure of the LC in the LC container as more and more LC fire retardant is used up from the LC container to create the RTU fire retardant product. The Inventors have appreciated that, given the foregoing circumstances of disparate viscosities for LC and water, respectively, and changing head pressure of the LC, a manually- operated proportioning valve employed in a conventional LC mix plant as shown in FIG.1 will be ineffective at reliably mixing an ultra-high viscosity LC and water to create RTU product. In particular, the Inventors have recognized that a proportioning valve of an LC mix plant needs to be dynamically operated to periodically change (e.g., in some instances continuously change) the respective aperture sizes for an ultra-high viscosity LC fire retardant and the water within the valve to accordingly adjust corresponding flow rates so as to effectively achieve a specified mix-ratio and desired concentration of retardant salt in the RTU fire retardant product. More generally, the Inventors have recognized the need to dynamically control the respective flow rates of an ultra-high viscosity LC fire retardant and water (whether or not a proportioning valve is used to mix these constituents), particularly in view of the significant viscosity differences and a constantly changing head pressure of the LC in the LC container. In view of the foregoing, the inventive concepts disclosed herein are directed to improved mix plants for dilution and effective mixing of high viscosity long-term fire retardant liquid concentrates with water to produce RTU fire retardant product with a desired concentration of retardant salt. Additionally, the improved mix plant for dilution and effective mixing can be utilized for lower viscosity concentrates to produce RTU fire retardant products. In example implementations, effective mixing of high viscosity LCs and water is achieved in part via automated feedback control of respective flow rates of the LC and the water. To facilitate improved quality control of the RTU product, in-line sensing of the RTU product is employed to regularly measure and digitally record one or more parameters representing a concentration of retardant salt in the RTU product as it is produced. One or more signals representing the measured parameter(s) are used as feedback to automatically adjust flow rates of the LC and the water so as to achieve a target concentration (e.g., weight Attorney Docket No. FFRS-012WO01 percent) of retardant salt in the RTU product and a target flow rate for the RTU product (to facilitate loading into an airtanker). In some aspects, the techniques described herein relate to a mix plant for providing a ready-to-use (RTU) fire retardant product containing at least one fire retardant compound for loading onto an aircraft, the mix plant including: a water tank to hold water; a liquid concentrate (LC) container to hold a liquid concentrate (LC) fire retardant containing the at least one fire retardant compound, wherein an LC head pressure of the LC fire retardant in the LC container changes as the LC fire retardant is consumed to provide the RTU fire retardant product; a single automated proportional mixing valve, fluidically coupled to the water tank and the LC container, to mix the water and the LC fire retardant and thereby form the RTU fire retardant product; at least one conduit, fluidically coupled to the single automated proportional mixing valve and a flow meter, to carry the RTU fire retardant product from the single automated proportional mixing valve; at least one pump, fluidically coupled to the at least one conduit, to pump the RTU fire retardant product through the at least one conduit; an in-line refractometer, positioned in the at least one conduit between the single automated proportional mixing valve and the flow meter so as to be in fluidic contact with the RTU fire retardant product, to measure an in-line refractive index of the RTU fire retardant product in the at least one conduit; and at least one controller, communicatively coupled to the in-line refractometer and the single automated proportional mixing valve, to automatically adjust at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the in-line refractive index measured by the in-line refractometer, to achieve a target refractive index of the RTU fire retardant product in a range of from 10 to 30 on the 10440 VP arbitrary scale. In some aspects, the techniques described herein relate to a mix plant, wherein the water tank includes a water level sensor to automatically refill the water tank with additional water as the water is consumed to provide the RTU fire retardant product so as to maintain an essentially constant water head pressure at an outlet of the water tank. In some aspects, the techniques described herein relate to a mix plant, further including: a first actuated valve coupled to an outlet of the water tank and communicatively coupled to the at least one controller, wherein the first actuated valve is responsive to a first signal output by the at least one controller to open and close the first actuated valve; and a second actuated valve coupled to an outlet of the LC container and communicatively coupled Attorney Docket No. FFRS-012WO01 to the at least one controller, wherein the second actuated valve is responsive to a second signal output by the at least one controller to open and close the second actuated valve. In some aspects, the techniques described herein relate to a mix plant, wherein: the at least one pump is communicatively coupled to the at least one controller and is responsive to at least one pump control signal output by the at least one controller to control a flow rate of the at least one pump. In some aspects, the techniques described herein relate to a mix plant, further including the flow meter, wherein: the at least one controller is communicatively coupled to the in-line refractometer, the flow meter and the single automated proportional mixing valve, to automatically adjust the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the in-line refractive index measured by the in-line refractometer and an in-line density of the RTU fire retardant product measured by the flow meter, to achieve a target refractive index of the RTU fire retardant product in a range of from 8 to 30 on the 10440 VP arbitrary scale. In some aspects, the techniques described herein relate to a method of providing a ready-to-use (RTU) fire retardant product containing at least one retardant compound, the method including: A) forming the RTU fire retardant product by creating a mixture of water and a liquid concentrate (LC) fire retardant containing the at least one retardant compound, wherein the LC fire retardant has a viscosity in a range of from between 1500 centipoise (cP) and 3000 cP; B) measuring at least one parameter representing a concentration of the at least one retardant compound in the mixture; and C) automatically adjusting at least one flow variable for each of the LC fire retardant and the water based at least in part on B), to: achieve a target weight percent of the at least one retardant compound in the RTU fire retardant product in a range of from 8% to 12%; and achieve a flow rate for the RTU fire retardant product in a range of from 200 gallons/minute to 1000 gallons/minute. In some aspects, the techniques described herein relate to a method of providing a ready-to-use (RTU) fire retardant product for loading onto an aircraft, the RTU fire retardant product containing at least one fire retardant compound, the method including: A) operating at least one pump to flow water from a water tank, and flow a liquid concentrate (LC) fire retardant containing the at least one fire retardant compound from a liquid concentrate (LC) container, through a single automated proportional mixing valve to form the RTU fire retardant product, wherein: an LC head pressure of the LC fire retardant in the LC container Attorney Docket No. FFRS-012WO01 changes during A); and the RTU fire retardant product is pumped through at least one conduit coupled between the single automated proportional mixing valve and a flow meter associated with the aircraft at a flow rate in a range of from 200 gallons/minute to 1000 gallons/minute; B) automatically and repeatedly measuring an in-line refractive index of the RTU fire retardant product, via an in-line refractometer disposed in the at least one conduit between the single automated proportional mixing valve and the flow meter associated with the aircraft, as the RTU fire retardant product is pumped through the at least one conduit so as to generate a plurality of refractive index measurements for the RTU fire retardant product; and C) automatically adjusting or maintaining at least one flow variable for each of the LC fire retardant and the water via operation of the single automated proportional mixing valve, based at least in part on the plurality of refractive index measurements generated in B), to achieve a target refractive index of the RTU fire retardant product in a range of from 8 to 30 on the 10440 VP arbitrary scale. In some aspects, the techniques described herein relate to a method, wherein the LC fire retardant has a viscosity in a range of from between 1500 centipoise (cP) and 3000 cP. In some aspects, the techniques described herein relate to a method, wherein in C), a target weight percent of the at least one fire retardant compound in the RTU fire retardant product is in a range of from 8% to 12%. In some aspects, the techniques described herein relate to a method, wherein in C), the target refractive index of the RTU fire retardant product is in a range of from 8.5 to 20.0 on the 10440 VP arbitrary scale. In some aspects, the techniques described herein relate to a method, wherein the at least one fire retardant compound includes at least one of magnesium chloride, ammonium phosphate, or polyphosphate. In some aspects, the techniques described herein relate to a method, wherein A) further includes: maintaining a water head pressure of the water in the water tank essentially constant during A). In some aspects, the techniques described herein relate to a method, further including: storing a digital record of at least some of the plurality of refractive index measurements generated in B). In some aspects, the techniques described herein relate to a method, further including, prior to A): receiving first user input, via a user interface, relating to a target mix ratio for the Attorney Docket No. FFRS-012WO01 water and the LC fire retardant to form the RTU fire retardant product; and adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. In some aspects, the techniques described herein relate to a method, wherein the water tank includes a first actuated valve at an outlet of the water tank, the LC container includes a second actuated valve at an outlet of the LC container, and the method further includes, prior to A): automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. In some aspects, the techniques described herein relate to a method, further including: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. In some aspects, the techniques described herein relate to a method, wherein in C) is performed after the flow rate of the RTU fire retardant product is at the target flow rate. In some aspects, the techniques described herein relate to a method, further including, prior to A): receiving third user input, via the user interface, relating to the range of the target refractive index for the RTU fire retardant product. In some aspects, the techniques described herein relate to a method, wherein C) further includes: C1) at a first time, comparing a first refractive index measurement of the plurality of refractive index measurements generated in B) with the range for the target refractive index of the RTU fire retardant product; C2) if the first refractive index measurement of the RTU fire retardant product is within the range for the target refractive index of the RTU fire retardant product, maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve; and C3) if the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product, adjusting the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. Attorney Docket No. FFRS-012WO01 In some aspects, the techniques described herein relate to a method, wherein C) further includes: C4) stopping the at least one pump in A) if fourth user input is received via the user interface relating to stopping operation of the at least one pump; and C5) stopping the at least one pump in A) if: fifth user input relating to a pre-set quantity of the RTU fire retardant product is received via the user interface; and an amount of the RTU fire retardant product pumped through the at least one conduit equals, approximately equals, or exceeds the pre-set quantity of the RTU fire retardant product. In some aspects, the techniques described herein relate to a method, further including: C6) repeating C1) and either C2) or C3) at a second time using a second refractive index measurement of the plurality of refractive index measurements. In some aspects, the techniques described herein relate to a method, wherein: the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product; and C3) includes: operating the single automated proportional mixing valve so as to adjust the at least one flow variable for each of the LC fire retardant and the water such that in B), the in-line refractive index of the RTU fire retardant product changes by approximately 0.1 on the 10440 VP arbitrary scale. In some aspects, the techniques described herein relate to a method, wherein C6) includes: C6a) waiting a predetermined time period following C3); and C6b) after waiting the predetermined time period, repeating C1) and either C2) or C3) at a second time using a second refractive index measurement of the plurality of refractive index measurements. In some aspects, the techniques described herein relate to a method, wherein: B) includes: B1) automatically and repeatedly measuring the in-line refractive index of the RTU fire retardant product, via the in-line refractometer disposed in the at least one conduit between the single automated proportional mixing valve and the flow meter associated with the aircraft, as the RTU fire retardant product is pumped through the at least one conduit so as to generate the plurality of refractive index measurements for the RTU fire retardant product; and B2) automatically and repeatedly measuring an in-line density of the RTU fire retardant product, via the flow meter associated with the aircraft, as the RTU fire retardant product is pumped through the at least one conduit so as to generate a plurality of density measurements for the RTU fire retardant product; and C) includes: automatically adjusting or maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the plurality of refractive index Attorney Docket No. FFRS-012WO01 measurements generated in B1) and the plurality of density measurements generated in B2, to achieve the target refractive index of the RTU fire retardant product in the range of from 8 to 30 on the 10440 VP arbitrary scale. All combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are part of the inventive subject matter disclosed herein. The terminology used herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally and/or structurally similar elements). FIG. 1 illustrates respective elements of a conventional LC mix plant at an airtanker base. FIG.2 illustrates an inventive mixing system for preparing (e.g., mixing or diluting) a long-term fire retardant for application to a fire according to one example implementation. FIG. 3 illustrates a method for providing a ready-to-use (RTU) fire retardant product for loading onto an aircraft, the RTU fire retardant product containing at least one fire retardant compound in accordance with the present technology. FIG. 4 illustrates a method of providing an RTU fire retardant product containing at least one retardant compound in accordance with the present technology. FIG. 5 illustrates a method of providing an RTU fire retardant product containing at least one retardant compound in accordance with the present technology. Attorney Docket No. FFRS-012WO01 DETAILED DESCRIPTION Components of Liquid Concentrates LC fire retardants may include one or more retardant compounds. The retardant compounds may include one or more inorganic compounds, one or more organic compounds, or a combination thereof. Table 1 below illustrates exemplary compounds, any one or more of which may be used, alone or in combination, as a retardant compound in LC fire retardants in accordance with the present technology. Table 1: Exem lar Retardant Com o nds M M w 2 1 C C w 1 2 M C N

1 Attorney Docket No. FFRS-012WO01 Na2SO4(H2O)x where x is H 1 ,

K2HPO4 Attorney Docket No. FFRS-012WO01 K2HPO4(H2O)x, where x

The retardant compound may be a salt. The salt may be a phosphate salt. Preferably the phosphate salt is a technical grade phosphate with low concentrations of heavy metals. The phosphate salt may include ammonium salts of ortho, pyro, tripoly, or tetrapoly phosphoric acid. The phosphate salt in the LC fire retardant composition may include one or more of the following: ammonium orthophosphates, ammonium pyrophosphates, ammonium polyphosphates having an average chain length of less than 20 phosphorus atoms. For example, the phosphate salt may include at least one of diammonium phosphate (DAP), diammonium orthophosphate (DAP), monoammonium phosphate (MAP), monoammonium orthophosphate (MAP), ammonium polyphosphate (APP). Instead of (or in addition to) ammonium salts of ortho, pyro, tripoly, or tetrapoly phosphoric acid, the phosphate salt may include a sodium phosphate salt. The sodium phosphate salt may include sodium salts of mono-, di-, tri-, tetra, and polyphosphates. The sodium phosphate salt in the LC fire retardant may include one or more of the following: monosodium phosphate (MSP), disodium phosphate (DSP), disodium phosphate hydrate, sodium ammonium phosphate (SAP), sodium ammonium phosphate hydrate (SAP-H), sodium tripolyphosphate (STPP), trisodium phosphate (TSP), and mixtures thereof. The disodium phosphate can be anhydrous, substantially free of any hydrate. Alternatively, or in combination with the anhydrous disodium phosphate, the disodium phosphate can be a hydrate, substantially free of any anhydrous. The hydrate may have the formula Na2HPO4(H2O)x, where x is about 1 to about 12. For example, x may be equal to at least one of 2, 7, 8, or 12. The disodium phosphate may contain a mixture of multiple different hydrates Na₂HPO₄(H₂O)_y, such that when measured, y constitutes an average weighted number of hydrates in the mixture, and thus y is not necessarily a whole number. For example, the average weighted value of y may be about 2.0 to about 12.0, preferably about 1.5 to about 11.5, more preferably about 2.5 to about 10.5, and more preferably about 3.5 to about 9.5. The sodium ammonium phosphate can be anhydrous, substantially free of any hydrate. Alternatively, or in combination with the anhydrous sodium ammonium phosphate, the sodium Attorney Docket No. FFRS-012WO01 ammonium phosphate can be a hydrate. The hydrate may have the formula NaPO4HNH4(H2O)x, where x is about 1 to about 4. For example, x may be equal to at least one of 1, 2, 3, or 4. The disodium phosphate may also contain a mixture of multiple different hydrates NaPO₄HNH₄(H₂O)_y, such that when measured, y constitutes an average weighted number of hydrates in the mixture, and thus y is not necessarily a whole number. For example, the average weighted value of y may be about 1.0 to about 4.0, preferably about 1.2 to about 3.9, more preferably about 1.4 to about 3.8, and more preferably about 1.6 to about 3.6. The sodium ammonium phosphate hydrate is preferably sodium ammonium phosphate tetrahydrate (SAP-TH) having the formula NaPO4HNH4(H2O)4. Instead of (or in addition to) ammonium salts of ortho, pyro, tripoly, or tetrapoly phosphoric acid and/or sodium phosphate salt(s), the phosphate salt may be a calcium phosphate salt. The calcium phosphate salt may include calcium salts of orthophosphates, di- and monohydrogen phosphates, and/or di- and polyphosphates. The calcium phosphate salt in the LC fire retardant may include one or more of the following: monocalcium phosphate (MCP), dicalcium phosphate (DCP), tricalcium phosphate (TCP), octacalcium phosphate (OCP), dicalcium diphosphate, calcium triphosphate, hydroxyapatite, Apatite, or tetracalcium phosphate (TTCP). Instead of (or in addition to) ammonium salts of ortho, pyro, tripoly, or tetrapoly phosphoric acid, sodium phosphate salt(s), and/or calcium phosphate salts, the phosphate salt may be a potassium phosphate salt. The potassium phosphate salt in the LC fire retardant may include one or more of the following: monopotassium phosphate (MKP), dipotassium phosphate, or tripotassium phosphate. The phosphate salt of the LC fire retardant may include an ammonium source. The ammonium source may be an ammonium salt. The ammonium source may be an ammonium phosphate salt. For example, when the phosphate salt includes ammonium. The ammonium phosphate salt in the LC fire retardant may include one or more of the following: diammonium phosphate (DAP), diammonium orthophosphate (DAP), monoammonium phosphate (MAP), monoammonium orthophosphate (MAP), ammonium polyphosphate (APP), sodium ammonium phosphate (SAP), or sodium ammonium phosphate hydrate (SAP-H). Instead of (or in addition to) an ammonium phosphate salt, the LC fire retardant may include a non- phosphate ammonium source. The non-phosphate ammonium source in the LC fire retardant may include one or more of the following: ammonium chloride, ammonium acetate, ammonium citrate, or ammonium sulfate. The retardant concentrate may contain no ammonium Attorney Docket No. FFRS-012WO01 phosphate, but when the retardant concentrate is diluted with water to make the final retardant product, the final retardant product may contain ammonium phosphates due to the exchange of ions in solution. The LC fire retardant may contain a mixture of phosphates. In certain embodiments, the mixture of phosphates has a molar ratio of ammoniacal nitrogen to phosphorus (N/P molar ratio) of about 0.4 to about 1.4, preferably about 0.6 to about 1.3, more preferably about 0.8 to about 1.1. For example, the N/P molar ratio is less than about 1.1, or is about 1. For example, the N/P molar ratio may be below 1.05, below 1.04, below 1.03, below 1.02, below 1.01, or below 1.00. In another embodiment, the N/P molar ratio is greater than about 1.9, for example about 1.9 to about 3.0, preferably about 2.0 to about 2.9, more preferably about 2.1 to about 2.7. For example, the N/P molar ratio may be above 1.95, above 1.96, above 1.97, above 1.98, above 1.99, or above 2.0. As used herein, “ammoniacal nitrogen,” or “phosphorus,” respectively, when referring to the nitrogen to phosphorus molar ratio (N/P molar ratio) refers to any ammoniacal nitrogen (NH4⁺) or phosphorus present in the formulation from any of the sources listed in Table 1. For example, the N/P ratio would not include any nitrogen or phosphorus from a dye not listed in Table 1. The liquid concentrate may further include a corrosion inhibitor to reduce or, in some instances, corrosion of various components exposed to the liquid concentrate (e.g., the pipes or tubes of the mixing system 100) and/or the final diluted product (e.g., the dispersal systems used in aircraft or ground vehicles to dispense the final diluted product). The components may be formed from various materials including, but not limited to, brass, iron, aluminum, steel, copper, and magnesium. The LC fire retardant and/or final diluted product may further include a corrosion inhibitor. The corrosion inhibitor may include an inhibitor for brass, iron, aluminum, steel, copper, and/or magnesium. The corrosion inhibitor may also include an inhibitor for any of the compounds listed in Table 1. The corrosion inhibitor for magnesium may include any corrosion inhibitors disclosed in Lamaka, S. V., et al. “Comprehensive screening of Mg corrosion inhibitors.” Corrosion Science 128 (2017), hereby incorporated by reference in its entirety. The corrosion inhibitor may include an alkyl (such as an alkyl amine) and/or one or more azoles. The corrosion inhibitor may include COBRATEC 928, Denatonium benzoate, benzoic acid, diammonium phosphate, monoammonium phosphate, Wintrol SB 25Na, or a combination of the above. The corrosion inhibitor may include one or more azoles. The corrosion inhibitor may be a Wintrol® Super Azole Mix (Wintrol® SAM-H90 from Wincom, Inc). The Wintrol® SAM-H90 is designed for aqueous application. Wintrol® SAM-H90 Attorney Docket No. FFRS-012WO01 provides corrosion resistance in highly corrosive environments caused by halogens, such chloride. Optionally, Wintrol® SAM-H38Na may be used as the corrosion inhibitor, alone or in combination with Wintrol® SAM-H90. The corrosion inhibitor may include but is not limited to, sodium selenite, sodium stearate, sodium lauryl sulfate, stearic acid, sodium benzoate, sodium fluoride, sodium phosphate, monosodium phosphate (MSP), disodium phosphate (DSP), disodium phosphate hydrate(s) (Na2HPO4(H2O)x, where x is about 1 to about 12), trisodium phosphate (TSP), monopotassium phosphate (MKP), dipotassium phosphate (DKP), dipotassium phosphate hydrate(s) (K2HPO4(H2O)x, where x is about 3 to about 6), tripotassium phosphate, tripotassium phosphate hydrate(s) (K3PO4(H2O)x, where x is about 3 to about 9), monoammonium phosphate (MAP), diammonium phosphate (DAP), triammonium phosphate, triammonium phosphate hydrate(s), iron pyrophosphate, sodium fumarate dibasic, sodium fumarate, magnesium phosphate, benzotriazole derivatives, sodium salts of benzotriazole and derivatives, aqueous mixtures of benzotriazole and derivatives, benzotriazole-5-carboxcylic acid, benzotriazole, butyl benzotriazole, sodium butyl benzotriazole, tolytriazole derivatives, sodium salts of tolytriazole and derivatives, aqueous mixtures of tolytriazole and derivatives, tetrathydro tolytriazole, tolytriazole, hydrogenated tolyltriazole and mixtures thereof, sodium tolytriazole, sodium tolytriazole (50% solution), 3- hydroxyphenyl-4-phenyl-5-mercapto-1,2,4-triazole (HPMT), 3-aminophenyl-4-phenyl-5- mercapto- 1,2,4-triazole (APMT), 3,4-diphenyl-5-mercapto- 1,2,4-triazole (DPMT), 3- cinnamyl-4-phenyl-5-mercapto- 1,2,4-triazole (CPMT), 1,8-napthalaldehydic acid, octadecylphosphonic acid, sodium dodecyl sulfonate (SDBS), Wintrol® BBT-25Na, Wintrol® BBT, Wintrol® THT-T, Wintrol® THT-35PG, Wintrol® THT-50K, Wintrol® SAM-H90, Wintrol SB 25Na, Wintrol® SAM-H38Na, Wintrol® SAM-H40(OS), Wintrol® SAM-B90, berberine, pyrrolidine benzylic, catechin, lysergic acid, carmine, fast green, aniline, vanillin, triethanolamine, low freeze grade triethanolamine (85% TEA and 15% water), N,N,N',N'- Tetrakis(2-hydroxyethyl)ethylenediamine, tris(hydroxymethyl)aminomethane (TRIS), Tris(hydroxymethyl)aminomethane hydrochloride (TRIS-HCl), p-chloroaniline, p- nitroaniline, p-methoxyaniline, p-methylaniline, p-cumate Na, sodium silicate, sodium molybdate, sodium molybdate dihydrate, disodium molbdate, disodium molybdate dihydrate, a biopolymer (such as rhamsan gum, xanthan gum, diutan gum, or welan gum), sodium silicofluoride (SSF), and dimercaptothiadiazole (DMTD), or a combination of the above. The final diluted product may be uncolored (i.e., clear, natural colored, or free of colorants), or it may be colored using a colorant. The colorant may be a fugitive colorant, a Attorney Docket No. FFRS-012WO01 non-fugitive colorant, or a combination of the two. The final diluted product has a first hue which is a color, i.e., either colorless or a color which blends with the normal vegetation and/or ground in the drop zone. This first hue may be grey or white or a combination of the two. The colorant initially colors the final diluted product to a second hue which contrasts with the hue of the ground vegetation. The colorant may be a fugitive component such as a dye or a dye which is dispersed in a matrix (i.e., a pigment), which fades over time and under ambient field conditions to a colorless or less highly colored hue. The colorant may be a mixture of an organic pigment (e.g., a fluorescent pigment) and inorganic pigment (e.g., iron oxide, titania, and/or titanium dioxide). Preferably the colorant is one that is compatible with the fire retardant salts described herein. The fugitive colorant may fade over time with exposure to sunlight. The fugitive colorant may also be a fast fade fugitive colorant that is designed to last a few hours to a few weeks, for example. Several fugitive component dyes and pigments can be used as a colorant. The colorant may be a dye(s) and/or a pigment(s). For example, many water-soluble dyes fade rapidly and there are so-called fluorescent pigments (fluorescent dyes encapsulated in a resin integument or dispersed in a thermoplastic as an emulsion) which are suspended in forest fire retardant compositions and which also fade rapidly to provide a fugitive effect. The colorant may be an agricultural, pesticide, or food-grade dye or combinations of such dyes that are red, pink, claret, and/or cerise. Examples of fugitive dyes and pigments include, but are not limited to, C.I. Basic Red I dye, 6BL dye, Basic Violet II dye, C.I. Basic Violet 11:1 (tetrachlorozincate), C.I. Basic Red 1:1, Basic Yellow 40, acid fuchsin, basic fuchsin, new fuchsin, acid red 1, acid red 4, acid red 8, acid red 18, acid red 27, acid red 37, acid red 88, acid red 97, acid red 114, acid red 151, acid red 183, acid red 183, fast red violet 1B base, solvent red, Rhodamine B, Rhodamine 6G, Rhodamine 123, Rhodamine 110 chloride, erythrosine B, Basacryl red, Phloxine B, rose Bengal, direct red 80, direct red 80, Sudan red 7B, Congo red, neutral red, Fluorescent Red Mega 480, Fluorescent red 610, Fluorescent red 630, Fluorescent Red Mega 520, Pylaklor Red S-361, Pylaklor Scarlet LX-6364A Pylam Bright Red LX-1895 Pylam Coral LX-1801, FD&C Red #3, FD&C Red #4, FD&C Red #40, FD&C Red #4 Lake, D&C Red #33, D&C Red #33 Lake, and encapsulated-dye pigments which are available commercially, e.g., the “AX” series pigments, supplied by Day-Glo Color Corp., Cleveland, Ohio. The dye may be Liquitint 564 (λ=564 nm) or Liquitint Agro Pink 564 (λ=564 nm) from Milliken & Company (Spartanburg, SC). The colorant may also be an organic pigment such as a fluorescent pigment. The fluorescent pigment may be Day-Glo Aurora pink or another pink, red, orange, or crimson (or Attorney Docket No. FFRS-012WO01 a combination of the four) fluorescent pigment dispersion. The fluorescent pigment may be UV sensitive and/or be substantially free of formaldehyde and/or have a Lab color spacing of “L” in a range from about 34 to about 89, “a” in a range from about 18 to about 83, and “b” in a range from about –61 to about 56, based on the International Commission of Illumination LAB color space model. The colorant may be a colorant from Greenville Colorants (New Brunswick, NJ) or Milliken & Company (Spartanburg, SC). For example, the colorant is a colorant that is compatible for use with the fire retardant salts described herein, such as colorants used in magnesium chloride dust-control and road-stabilization formulations, or in magnesium chloride de-icing formulations. The colorant may be Elcomine Scarlet NAS, Elcomine Scarlaet NAS EX, or Iron Oxide GC-110P from Greenville Colorants. The colorant may be a combination of Liquitint 564 and Iron Oxide GC-110P. The colorant of the final diluted product may be a dye or include encapsulated-dye fugitive pigments without ultraviolet absorbers. Compared to water soluble dyes, encapsulated-dye pigments are less likely to permanently stain the normal vegetation and/or ground in the drop zone. The fugitive component is present in an amount which provides a color (second hues) to the final diluted product which is contrasts with the color of the vegetation and/or ground in the drop zone (normally green, blue-green and/or brown). Advantageously, the second hue is red, orange or pink. The color of the dye may be red, orange, purple, or pink or any combination of the four. Preferably, the dye is one that is compatible with the fire retardant salts described herein. Alternatively, the final diluted product may be colorless if no colorant is added. The colorant may also include a non-fugitive component, i.e., a component which is insoluble in the carrier liquid and which, if colored, does not necessarily fade after aerial application of the final diluted product. The non-fugitive component of the colorant is present in an amount sufficient to improve the aerial visibility of the composition when it is first applied to the vegetation. However, the non-fugitive component is present in less than an amount which prevents the composition from thereafter fading a neutral color. The colorant may be a combination of the fugitive and non-fugitive components. The non-fugitive component in the final diluted product may be iron oxide (Fe2O3 and/or Fe3O4). The iron oxide may be present in combination with the fugitive colorant described above and titanium dioxide or it may be present alone. The weight of the non-fugitive colorant may contain a minimum of at least 12 Attorney Docket No. FFRS-012WO01 grams of the non-fugitive colorant in accordance with Specification 5100–304d (January 7, 2020), which is hereby incorporated by reference in its entirety. The weight percent of colorant (e.g., fluorescent pigment), relative to the amount of the retardant compound in the liquid concentrate, is about 0.1% to about 15.0%, preferably about 0.2% to about 12.0%, more preferably about 0.3% to about 10.0%, and more specifically about 0.4% to about 8.0%. For example, the weight percent of colorant, relative to the amount of the retardant compound in the liquid concentrate, is about 0.5% to about 5.0%. The liquid concentrate may also include an inorganic pigment. The inorganic pigment may act as a colorant. The inorganic pigment may include but is not limited to Iron Oxide, titanium dioxide, magnesium hydroxide, cobalt blue, cerulean blue, malachite, earth green, raw umber, raw sienna, iron black, or burnt sienna. The Iron Oxide may act as an opacifier. The titanium dioxide may act as a pigment, for example, to provide a white pigment. The titanium dioxide may also act as a photo-responsive material to create opacity by scattering light or by protecting the components of the liquid concentrate from UV degradation. The weight percent of inorganic pigment, relative to the amount of the retardant compound in the liquid concentrate, is about 0.02% to about 4.0%, preferably about 0.04% to about 3.5%, more preferably about 0.06% to about 3.0%, and more specifically about 0.08% to about 2.5%. For example, the weight percent of inorganic pigment, relative to the amount of the retardant compound in the liquid concentrate, is about 0.1% to about 2.0%. The weight percent of total colorant, relative to the amount of the retardant compound in the liquid concentrate, is about 0.1% to about 30.0%, preferably about 0.2% to about 28.0%, more preferably about 0.3% to about 25%, and more specifically about 0.4% to about 20.0%. For example, the weight percent of total colorant, relative to the amount of the retardant compound in the liquid concentrate, is about 0.5% to about 18.0%. The weight percent of the retardant compound(s) relative to the total weight of the liquid concentrate may be about 5% to about 85%, for example about 20% to about 80%, preferably about 30% to about 75%, and particularly about 35% to about 70%. The weight percent of the retardant compound(s) relative to the total weight of the liquid concentrate may be in a range from about 8% to about 12%. The liquid concentrate may be any of the liquid concentrates and/or intermediate liquid concentrates formed from dry concentrates disclosed in the following: U.S. Patent Application No.16/894,214, filed June 5, 2020; U.S. Patent Application No.17/031,024, filed September Attorney Docket No. FFRS-012WO01 24, 2020; U.S. Patent Application No. 17/214,266, filed March 26, 2021; U.S. Patent Application No.17/458,002, filed August 26, 2021; U.S. Patent Application No.17/552,196, filed December 15, 201, all of which are incorporated by reference in their entirety. The viscosity of the liquid concentrate may be in the range of about 10 cP to about 10,000 cP, For example, the viscosity of the liquid concentrate may be about 100 cP to about 8000 cP, preferably about 500 cP to about 7000 cP, more preferably about 1000 cP to about 6000 cP, more preferably about 1500 cP to about 3000 cP, and more preferably the viscosity may be about 1750 cP to about 2250 cP at 70 °C. For example, the viscosity of the liquid concentrate may be about 1970 cP to about 2090 cP at 70°C. To form the final diluted product, the liquid concentrate may be diluted with water. In other words, the final diluted product includes a first amount of liquid concentrate and a second amount of water. The mixing ratio, which is defined as the ratio of water to liquid concentrate may be about 45:1 to about 0.2:1 (water:liquid concentrate), preferably about 20:1 to about 0.5:1, more preferably about 10:1 to about 0.75:1, and specifically about 5:1 to about 1:1. For example, the liquid concentrate, may be diluted at a 2:1 mixing ratio (water:liquid concentrate) to form the final diluted product. As another example, the liquid concentrate, may be diluted at a mixing ratio of 1.895:1 (water:liquid concentrate) on a weight/weight basis. The liquid concentrate may be diluted with water so that the final diluted product has a retardant compound (e.g., salt) weight percent of about 2% to about 70%, preferably about 5% to about 40%, more preferably about 7% to about 30%. For example, the concentration of retardant compound (e.g., salt) in final diluted product is about 8% to about 25%. The liquid concentrate may be diluted with water so that the final diluted product has a retardant concentration of about 300 grams to about 900 grams of retardant per gallon of water, preferably about 450 grams to about 800 grams of retardant per gallon of water, more preferably about 500 grams to about 750 grams of retardant per gallon of water. The final diluted product is a long-term forest fire retardant with improved aerial visibility for either a direct or indirect attack of a forest fire. The resulting final diluted product may be an opaque reddish suspension that resists settling. The final diluted product may be mixed approximately every 7–10 days to ensure uniform density and homogeneity. The final diluted product may be any of the final diluted products disclosed in the following: U.S. Patent Application No.16/894,214, filed June 5, 2020; U.S. Patent Application No. 17/031,024, filed September 24, 2020; U.S. Patent Application No. 17/214,266, filed Attorney Docket No. FFRS-012WO01 March 26, 2021; U.S. Patent Application No.17/458,002, filed August 26, 2021; U.S. Patent Application No. 17/552,196, filed December 15, 2021; U.S. Patent Application No. 18/061,542, filed December 5, 2022. Each of the aforementioned applications is incorporated by reference in their entirety. The viscosity of the final diluted product can be adjusted to accommodate a variety of aircrafts and ground-based vehicles by adjusting the amounts of thickening agent(s) added to the liquid concentrate prior to its dilution or by adjusting the dilution factor of the liquid concentrate. In some versions, the final diluted product may be a medium viscosity long-term retardant. The viscosity of the medium viscosity diluted retardant may be in the range of 300 cP to 800 cP, and more preferably the viscosity may be about 460 cP to about 490 cP at 70°F. In one embodiment, the final diluted product has a pH of about 4.0 to about 10.0, preferably about 4.5 to about 9.8, more preferably about 5.0 to about 9.5, and more preferably about 5.5 to about 9.0. For example, the pH of the final diluted product may be about 5.5, about 5.6, about 5.7, about 5.8, about 5.9, about 6.0, about 6.1, about 6.2, about 6.3, about 6.4, about 6.5, about 6.6, about 6.7, about 6.8, about 6.9, about 7.0, about 7.1, about 7.2, about 7.3, about 7.4, about 7.5, about 7.6, about 7.7, about 7.8, about 7.9, about 8.0, about 8.1, about 8.2, about 8.3, about 8.4, about 8.5, about 8.6, about 8.7, about 8.8, about 8.9, about 9.0, or any value in between 5.5 and 9.0.The freezing temperature of the final diluted product may be in the range of 15°F to 25°F. Once blended with water, the final diluted product may be a homogeneous, stable fluid. Mixing System FIG.2 illustrates an inventive mixing system 100 (also referred to as a mix plant) for preparing (e.g., mixing or diluting) a long-term fire retardant for application to a fire, according to one example implementation. The mixing system 100 may be used for preparing a long-term fire retardant diluted product by diluting a long-term fire retardant liquid concentrate with a solvent such as water. The resulting diluted product is in a form suitable to fight (e.g., suppress, retard, contain) forest fires via aerial- or ground-based applications. In some versions, the mixing system 100 may be located at or near a firefighting dispatch location (e.g., at an airfield proximate to a forest fire), so that the mixing system 100 may prepare the fire retardant diluted product for convenient deployment to the forest fire. In other versions, the mixing system 100 may be disposed at other locations relevant for firefighting or storing fire retardants. Attorney Docket No. FFRS-012WO01 The fire retardant liquid concentrate, described in more detail below, is a viscous liquid having one or more fire retardant compounds dissolved in water at a high concentration. For example, the viscosity of the liquid concentrate at ambient temperature may be in a range of from about 50 centipoise (cP) to about 5,000 cP, or more generally in a range of from about 10 centipoise (cP) to about 10,000 cP. As an illustrative comparison, fluids that fall within this viscosity range include glycerin, corn syrup, and honey. As a reference, the viscosity of water at ambient temperature is about 1 cP. To produce the fire retardant diluted product suitable for application to a fire, the liquid concentrate is mixed with water for dilution. However, because of the relatively higher viscosity of the fire retardant liquid concentrate, the Inventors have recognized and appreciated that conventionally it is difficult to mix the liquid concentrate with water in precise mixing ratios. This problem is further exacerbated when mixing the liquid concentrate and water at relatively higher flow rates (e.g., 500 gallons per minute). In spite of these conventional mixing challenges, the ability to effectively control the mixing ration of liquid concentrate to water is important to ensure that the diluted product meets the specifications set by fire management services. For example, the US Forest Service specifies standards for a forest fire retardant to qualify for use by the US Forest Service, including the standards described in Forest Service Specification 5100-304d, hereby incorporated by reference in its entirety. The mixing system 100 addresses these problems by providing a mixing system that can effectively and accurately mix liquid concentrate with water at a desired volume-to- volume (e.g., gallon-to-gallon) water-to-liquid concentrate mixing ratio in a range of from about 45:1 to about 0.2:1 (water:liquid concentrate). In one aspect, the mixing ratio may be varied throughout this range in significantly small increments (e.g., essentially continuously), notwithstanding significant viscosity differences between the liquid concentrate and the water. In another aspect, the mixing system 100 creates a diluted product at a production rate (also called a flow rate) in a range of about 100 gallons per minute (gpm) to about 1200 gpm (examples of production rates include, but are not limited to, 100 gpm, 500 gpm, 1000 gpm, or 1200 gpm). As discussed in further detail below, in one example implementation the mixing system 100 includes one or more “in-line” sensors, i.e., disposed in the flow of the diluted product, to sense one or more measurable characteristics of the diluted product. The one or more sensed characteristics are input to a controller that in turn controls one or more valves and/or one or more pumps to vary a flow rate of either or both of the water and the liquid Attorney Docket No. FFRS-012WO01 concentrate so as to in turn vary the mixing ratio, based at least in part on the one or more sensed characteristics of the diluted product. Mixing system 100 may include an LC container 120 at least partially filled with liquid concentrate 122 and a solvent container 130 (equivalently, water tank 130) at least partially filled with solvent 132. Solvent 132 may be, e.g., water, and may be added to solvent container 130 through a solvent source 138. A distribution of solvent 132 from solvent source 138 may be controlled by a float valve 136, which may be configured to distribute water into solvent container 130 based on a level of solvent 132, e.g., to distribute solvent 132 into solvent container 130 when a level of solvent 132 is below a threshold. Float valve 136 may include a float 137 configured to float on top of solvent 132 and be displaced by solvent 132. When a level of solvent 132 is high enough, float 137 will be displaced such that float valve 136 is closed and solvent 132 ceases flowing. Liquid concentrate 122 may be any suitable fire retardant compound in accordance with the present technology, e.g., a fire retardant compound listed in Table 1. Liquid concentrate 122 may have a suitable viscosity as discussed above, e.g., between about 1500 cP and about 3000 cP, although lower viscosities are possible, e.g., about 1 cP to about 50 cP, about 25 cP to about 75 cP, about 50 cP to about 150 cP, about 100 cP to about 800 cP, about 500 cP to about 1000 cP, about 800 cP to about 1500 cP, or the like. Each of liquid concentrate 122 and solvent 132 may be apportioned through respective distribution valves. For example, LC container 120 may include LC distribution valve 124 and solvent container 130 may include solvent distribution valve 134. LC distribution valve 124 and solvent distribution valve 134 may be communicatively coupled to a controller 110, which may be configured to transmit one or more signals controlling an operation of LC distribution valve 124 and/or solvent distribution valve 134. For example, controller 110 may cause LC distribution valve 124 and solvent distribution valve 134 to open and allow a mixing of liquid concentrate 122 and solvent 132 to form a final diluted product, which may consume both the solvent (e.g., water) and the LC fire retardant as the two mix to form the final diluted product (e.g., an RTU fire retardant product). Controller 110 may be communicatively coupled to a user interface 112, which may be a computer, tablet, laptop, desktop, smartphone, touch screen, kiosk, or any suitable device for receiving information and/or instructions from a user. User interface 112 may include a data storage and/or memory for storing information, such as information related to an Attorney Docket No. FFRS-012WO01 operation of mixing system 100. For example, user interface 112 may be used to store a digital record of at least some of a plurality of measurements related to refractive index, flow rate, viscosity, pH, density, or any suitable measurement. A user may input one or more parameter values for a final diluted product, which may be created by mixing liquid concentrate 122 and solvent 132 in accordance with the parameter values. For example, a user may input parameter values for one or more of refractive index, density, viscosity, pH, mass flow, conductivity, flow rate, type of liquid concentrate 122, type of solvent 132, and/or selective ion concentration of the final diluted product. Liquid concentrate 122 and solvent 132 may flow through piping 170 (equivalently, conduit 170) . Mixing system 100 may include one or more pumps 150, including LC pump 150a, solvent pump 150b, and Final diluted product pump 150c. Pumps 150 may be any suitable type of pump, e.g., a mechanical pump, a siphon pump, etc. Each respective pump of pumps 150 may be disposed downstream of LC distribution valve 124 and solvent distribution valve 134. In an alternative aspect, LC pump 150a may be disposed upstream of LC distribution valve 124 and solvent pump 150b may be disposed upstream of solvent pump 150b. Each pump of pumps 150 may be further configured to mix the diluted product discharged from the outlet port of the proportional mixing valve. Each pump may have a variable pumping speed. Controller 110 may be further communicatively coupled to each pump and further configured to modulate the variable pumping speed based on sensor data from pumps 150 and/or other sensors within mixing system 100. Mixing system 100 may further include a static mixer fluidically coupled to a mixing junction 172, Final diluted product pump 150c, and/or final diluted product valve 174 to mix the final diluted product discharged from the outlet port of the final diluted product valve 174. The mixing junction 172 may include a main body defining a cavity and having a first inlet port for liquid concentrate to enter the cavity, a second inlet port for water to enter the cavity, and an outlet port to discharge a mixture of the liquid concentrate and the water. The mixing junction 172 may further include a modulating element disposed within the cavity. The modulating element may be movable within the cavity and positioned to partially or fully obstruct the first inlet port and/or the second inlet port in order to modify the proportion of Attorney Docket No. FFRS-012WO01 liquid concentrate and/or water entering the cavity and, thus, a mixing ratio of the liquid concentrate and the water. The modulating element may be coupled to an actuator, which may be used to adjust the modulating element (e.g., by moving or rotating the modulating element). The actuator may be various actuators including, but not limited to, an electric motor, a solenoid, a pneumatic actuator, a hydraulic actuator, and any combinations of the foregoing. The actuator may comprise a handle for manual actuation. The actuator may also be communicatively coupled to the controller 110 to receive control signals from the controller 110 and adjust the modulating element based on the control signals. For example, the control signals may be generated based on one or more conditions of the final diluted product discharged from the outlet port measured by the one or more sensors of measurement device 140. As illustrated in FIG.2, one or more signals from measurement device 140, which may represent an in-line concentration measurement of the final diluted product are input to controller 110. The controller 110 in turn controls the flow of one or more of the liquid concentrate 122, the solvent 132, or the final diluted product based on the in-line concentration measurement. The controller 110 optionally may also receive another signal provided by a flow meter to facilitate automated control of the flow of the liquid concentrate 122, solvent 132, and/or the final diluted product. In one example implementation, measurement device 140 may include an in-line refractometer configured to measure a concentration of final diluted product after mixing at mixing junction 172 ; examples of refractometers effectively employed by the Inventors for this purpose include, but are not limited to, the L-Rix series manufactured by Anton Paar. Mixing system 100 enables automated variable flow control for each of the liquid concentrate 122, solvent 132, and final diluted product based on one or more signals provided by the controller 110, wherein these one or more signals in turn are based on one or more in- line concentration measurements from measurement device 140 (e.g., in-line refractive index measurements provided by an in-line refractometer, one or more signals provided by a flow meter, etc.). It should be appreciated that in various inventive implementations, such automated variable flow control may be achieved in multiple ways. In an embodiment, mixing system 100 may include a plurality of measurement devices 140 disposed on various portions of piping 170, LC container 120, solvent container 130, or any suitable portion of mixing system 100. Attorney Docket No. FFRS-012WO01 One or more sensors of measurement device 140 may be disposed in-line with the flow of final diluted product to continuously and directly monitor the properties of the final diluted product produced by the mixing system. This may be accomplished, for example, by placing the one or more sensors within piping 170 or tube carrying the final diluted product, within a side-stream sampling line fluidically coupled to the main pipe or tube, or onto a window coupled to piping 170. A flow rate of a final diluted product may be measured by flow meter 160, which may be disposed at a portion of piping 170 adjacent to an aircraft 180 (such as a firefighting air tanker) or an RTU product container 190. A final diluted product may be stored or loaded after mixing. For example, the final diluted product may be stored as RTU product 192 in RTU product container 190. RTU product container 190 may be used to provide storage for RTU product 192 (e.g., hours, days, weeks, months, or the like). A final diluted product may be loaded onto aircraft 180 via loading hose 176. A final diluted product may be loaded onto aircraft 180 directly after mixing through mixing junction 172 or may be loaded onto aircraft 180 from RTU product container 190. In one non-limiting example, the one or more sensors of measurement device 140 may include a refractometer to measure the refractive index of the diluted product, which may vary appreciably in response to small changes in the mixing ratio of the fire retardant liquid concentrate and water and is less affected by the presence of bubbles in the diluted product. Although the components of a refractometer are generally susceptible to corrosive damage when exposed to corrosive compounds, such as magnesium chloride or, more generally, halides, phosphates, sulfates, carbonates, and/or hydroxides, the mixing systems disclosed herein may reduce or, in some instances, mitigate corrosive damage to the refractometer by using liquid concentrates that include corrosion inhibitors. Controller 110 may be communicatively coupled to pumps 150 and configured to control a flow of liquid concentrate 122, solvent 132, and final diluted product using one or more of pumps 150, LC distribution valve 124, solvent distribution valve 134, final diluted product valve 174, and measurements from measurement device 140. For example, controller 110 may increase or decrease a speed of LC pump 150a based on one or more refractive index measurements indicating a concentration of liquid concentrate 122 in a final diluted product. For example, in one inventive implementation, respective variable pumps responsive to the controller 110 may be employed for the LC, the water, and the RTU product, wherein a Attorney Docket No. FFRS-012WO01 mixing junction for the LC, the water, and the RTU product comprises a T-shaped or Y- shaped junction (also referred to conventionally as a “pipe wye”). In another inventive example, respective adjustable aperture valves responsive to the controller 110 may be employed for each of the LC and the water, together with a T-shaped or Y-shaped pipe wye and a single pump for the RTU product (which also may be responsive to the controller 110). In yet another example, an automated proportional mixing valve responsive to the controller 110 may be employed together with a single pump for the RTU product (which also may be responsive to the controller 110), downstream of the automated proportional mixing valve; alternatively, an automated proportional mixing valve responsive to the controller 110 may be employed with respective pumps for the LC and the water (which also may be responsive to the controller 110), upstream of the automated proportional mixing valve. Other permutations and combinations of the foregoing arrangements also are contemplated by the Inventors and would be readily understood by those of skill in the art with the benefit of this disclosure. Following below are two non-limiting illustrative examples of inventive systems and methods according to the present disclosure: Example 1 A mixing system comprising: • a water source o a tank that is equipped with a float valve or other water level sensor that automatically activates when the water level drops below a certain level to start refilling the tank and maintain a minimum head pressure and an actuated valve on the outlet of the tank that is connected by a pipe to one port of an actuated proportional mixing valve. o the actuated valve on the solvent tank is connected to a controller that can open or close the valve by sending a signal. • a liquid concentrate source o a tank with liquid concentrate (LC) with an actuated valve on the tank and a pipe that connects the valve on the LC container to the one port of an actuated proportional mixing valve. Attorney Docket No. FFRS-012WO01 o the actuated valve on the LC container is connected to a controller that can open or close the valve by sending a signal. • an actuated proportional mixing valve connected to a controller, and with one input port connected by a pipe to an actuated valve on the water source and second input port connected by a pipe to an actuated valve on the liquid concentrate (LC) source, and an output port. o the actuated proportional mixing valve is connected to a controller that can adjust the proportional mixing valve by sending a signal and can adjust the mix ratio such that only water is passed through the proportional mixing valve, only LC is passed through the proportional mixing valve, or any proportional ratio of water to LC between 0% and 100% will pass through the proportional mixing valve. • a pump, such as a centrifugal pump, wherein the intake port is connected to the output of the actuated proportional mixing valve and the discharge is connected to a storage tank with pipes. o the pump is connected to a centralized controller with a variable frequency drive that can activate or deactivate the pump with a signal and can control the flow rate of the pump between 0% and 100% of its output capacity after activating it • a refractive index sensor that is mounted downstream of the discharge of the pump in-line with storage tank. o the window of the refractive index sensor is in fluidic contact with the product in the pipe that connects the pump to the storage tank. • A controller that is connected to a power source, the actuated valve on the water source, the actuated valve on the LC source, at least one sensor, a variable frequency drive, and the pump. A ready to use (RTU) long-term fire retardant is prepared by the following: 1. Power is provided to the system and the controller runs through an automated start-up routine to check connectivity to and status of each of the components and then provides a ready signal to the operator. Attorney Docket No. FFRS-012WO01 The operator will set initial parameters based on the specific retardant that is being mixed and the desired flow rate into the RTU retardant storage tank, and will command the system to run. The system will then adjust the initial state of the proportional mixing valve to match the desired mix ratio for the LC, e.g. if the mix ratio for the LC is 1 gallon of LC to 2.4 gallons of water the proportional mixing valve will adjust to a configuration that will allow 2.4 times more water than LC to pass through the proportional mixing valve. The controller will then send signals to open the actuated valves on the water source and the LC source. The controller will then ramp up the pump to the desired flow rate that was input by the operator, which will pull in water and LC from their respective sources through the valves and pipes on the respective sources into the proportional mixing valve, combining them at the desired ratio. The combined fluids will then travel from the mixing valve through a section of pipe into the pump. The pump will help homogenize the mixture before sending it to the storage tank or an airtanker. As the product is transferred to the storage tank or air tanker it will flow past the refractive index sensor and be measured. The refractive index sensor will transmit the refractive index values of the mixed RTU product back to the controller where the measured value will be compared to the target value. If the measured refractive index of the mixed ready to use product that is being transferred to the storage tank or air tanker is within the tolerance that was entered by the operator the system will maintain all settings and continue to monitor the output readings of the refractive index sensor and operate until either the operator stops the system, a pre-set quantity of mixed ready to use retardant has been produced, or the refractive index of the mixed ready to use retardant that is being transferred to the storage tank or air tanker is out of tolerance. If at any point the controller detects refractive index value that is out of tolerance, the system will respond accordingly. For example, if the refractive index value that the sensor is detecting is below the target value, the system will adjust the proportional mixing valve such that more concentrate and less water is allowed to pass through the proportional mixing valve. The adjustments will be made in small steps allowing for Attorney Docket No. FFRS-012WO01 enough time after the adjustment at the proportional mixing valve for the mixed product with the new ratio to reach the refractive index sensor and the sensor to transmit the refractive index values back to the controller. If the adjustments made to the mixing ratio have brought the refractive index of the mixed product back into tolerance the system will maintain those values until either the operator stops the system, a pre-set quantity of mixed ready to use retardant has been produced, or the refractive index of the mixed ready to use retardant that is being transferred to the storage tank is out of tolerance. If the refractive index is still out of tolerance, the system will repeat the process adjusting the proportional mixing valve by another small step and waiting until the new refractive index value has been obtained and either maintain or repeat the process until the refractive index of the product being transferred to the storage tank is within tolerance. When the measured refractive index of the mixed ready to use product that is being transferred to the storage tank is within the tolerance that was entered by the operator, the system will maintain all settings and continue to monitor the output readings of the refractive index sensor and operate until either the operator stops the system, a pre-set quantity of mixed ready to use retardant has been produced, or the refractive index of the mixed ready to use retardant that is being transferred to the storage tank is out of tolerance. Example 2: A mixing system comprising: • a solvent source o a tank that is equipped with a float valve or other level sensor that automatically activates when the solvent (e.g., water) level drops below a certain level to start refilling the tank and maintain a minimum head pressure and an actuated valve on the outlet of the tank that is connected by a pipe to one port of an actuated proportional mixing valve o the actuated valve on the solvent tank is connected to a controller that can open or close the valve by sending a signal. • a liquid concentrate source Attorney Docket No. FFRS-012WO01 o a tank with liquid concentrate (LC) with an actuated valve on the tank and a pipe that connects the valve on the LC container to the one port of an actuated proportional mixing valve. o the actuated valve on the LC container is connected to a controller that can open or close the valve by sending a signal. • an actuated proportional mixing valve connected to a controller, and with one input port connected by a pipe to an actuated valve on the water source and second input port connected by a pipe to an actuated valve on the liquid concentrate (LC) source, and an output port. o the actuated proportional mixing valve is connected to a controller that can adjust the proportional mixing valve by sending a signal and can adjust the mix ratio such that only water is passed through the proportional mixing valve, only LC is passed through the proportional mixing valve, or any proportional ratio of water to LC between 0% and 100% will pass through the proportional mixing valve. • a pump, such as a centrifugal pump, wherein the intake port is connected to the output of the actuated proportional mixing valve and the discharge is connected to a storage tank with pipes. o the pump is connected to a centralized controller with a variable frequency drive that can activate or deactivate the pump with a signal and can control the flow rate of the pump between 0% and 100% of its output capacity after activating it. • a refractive index sensor that is mounted downstream of the discharge of the pump in-line with storage tank. o the window of the refractive index sensor is in fluidic contact with the product in the pipe that connects the pump to the storage tank. • 1 or more additional sensor sensors (density in this example) that is mounted downstream of the discharge of the pump in-line with storage tank. o the sensor is mounted in the fluid stream. Attorney Docket No. FFRS-012WO01 • A controller that is connected to a power source, the actuated valve on the water source, the actuated valve on the LC source, at least one sensor, a variable frequency drive, and the pump. A ready to use (RTU) long-term fire retardant is prepared by the following: 1. Power is provided to the system and the controller runs through an automated start-up routine to check connectivity to and status of each of the components and then provides a ready signal to the operator. 2. The operator will set initial parameters based on the specific retardant that is being mixed and the desired flow rate into the RTU retardant storage tank, and will command the system to run. 3. The system will then adjust the initial state of the proportional mixing valve to match the desired mix ratio for the LC, e.g. if the mix ratio for the LC is 1 gallon of LC to 2.4 gallons of water the proportional mixing valve will adjust to a configuration that will allow 2.4 times more water than LC to pass through the proportional mixing valve. 4. The controller will then send signals to open the actuated valves on the water source and the LC source. 5. The controller will then ramp up the pump to the desired flow rate that was input by the operator, which will pull in water and LC from their respective sources through the valves and pipes on the respective sources into the proportional mixing valve, combining them at the desired ratio. The combined fluids will then travel from the mixing valve through a section of pipe into the pump. The pump will help homogenize the mixture before sending it to the storage tank. 6. As the product is transferred to the storage tank it will flow past both the refractive index sensor and density sensors and will be measured. The refractive index sensor and density sensor will transmit the refractive index and density values of the mixed RTU product back to the controller where the measured values will be compared to the target value. 7. If both the measured refractive index and density of the mixed ready to use product that is being transferred to the storage tank is within the tolerance that was entered by Attorney Docket No. FFRS-012WO01 the operator the system will maintain all settings and continue to monitor the output readings of the refractive index sensor and operate until either the operator stops the system, a pre-set quantity of mixed ready to use retardant has been produced, or the refractive index of the mixed ready to use retardant that is being transferred to the storage tank is out of tolerance. If at any point the controller detects one of the sensors that is out of tolerance, the system will respond accordingly. For example, in one implementation, one or more sensors may be configured to provide a caution or warning of an out of tolerance condition but allow the system to continue to run without adjusting the proportional mixing valve; in a different example, one or more sensors may be configured to provide an ”alarm” state if an out of tolerance condition exists, and adjust the proportional mixing valve. Following below are additional details of nonlimiting examples in which multiple sensors are employed: a. A given sensor (refractive index or density) may be configured as a ‘warning’ sensor or an ‘alarm/correct’ sensor. Such a designation may apply to all values of a given sensor’s output outside of the tolerance range, or some values may be warning, and some alarm/correct (e.g., within X% outside of the tolerance range would be warning, and beyond X% outside of the tolerance range would be alarm, where X can be 1, 5, or 10, for example). b. For example, if the density is designated as warning and the refractive index is designated as alarm/correct, if the refractive index is within tolerance but the density is not, the system may send warnings to the user. The system will continue to run as normal until either the density is back within specification, the density meets an alarm/correct state, or the mixing is completed. If the refractive index is out of specification with the alarm/correct setting, if the controller detects that the refractive index value is above the desired target, the system will adjust the proportional mixing valve such that less concentrate and more water is allowed to pass through the proportional mixing valve. c. One metric out of specification, others are acceptable. For example, if the controller detects that the refractive index value is out of tolerance, but the density is within tolerance, the system will determine if the refractive index is below or above the desired target. If the system is above the target, the system Attorney Docket No. FFRS-012WO01 will adjust the proportional mixing valve such that less concentrate and more water is allowed to pass through the proportional mixing valve. Similarly, if the density is too high, the system will adjust the proportional mixing valve such that less concentrate and more water is allowed to pass through the proportional mixing valve. d. Multiple metrics out of specification. If the controller detects that both the refractive index and density values are out of tolerance, the system will determine if the density and refractive index are below or above the desired target. If they require adjustment in the same direction (i.e. if they are both above the target), the system will adjust the proportional mixing valve such that less concentrate and more water is allowed to pass through the proportional mixing valve. Similarly, if both are too low, the system will adjust the proportional mixing valve such that more concentrate and less water is allowed to pass through the proportional mixing valve. e. There are cases that may occur where one value is below the threshold and one is above. While this is unlikely to occur, the system should shut down and alert the user. f. The adjustments described in a-e are made in small steps allowing for enough time after the adjustment at the proportional mixing valve for the mixed product with the new ratio to reach the refractive index sensor and the sensor to transmit the refractive index values back to the controller. As non-limiting examples, small steps of adjustment may include adjusting one or more flow rates by 0.5%, 1%, 5%, or 10%. A non-limiting example of an amount of time to allow a new ratio to reach the refractive index sensor may be on the order of milliseconds or a fraction of a second, such that in practice, the response of the feedback is essentially instantaneous. If the adjustments made to the mixing ratio have brought the sensor output of the mixed product back into tolerance the system will maintain those values until either the operator stops the system, a pre-set quantity of mixed ready to use retardant has been produced, or the mixed ready to use retardant that is being transferred to the storage tank is again out of tolerance. If the measured property is still out of tolerance, the system will repeat the process adjusting the proportional mixing valve by another small step and waiting until the new sensor output value has been Attorney Docket No. FFRS-012WO01 obtained and either maintain or repeat the process until the refractive index of the product being transferred to the storage tank is within tolerance. [00109] It should be appreciated that the foregoing example of using multiple sensors to provide feedback relating to a retardant salt concentration in the RTU fire retardant product is provided primarily for the purpose of illustration. In general, in various implementations involving multiple sensors, respective sensor output signals from multiple sensors may be combined mathematically (e.g., via the controller) to provide a “composite signal” that is used by the controller to provide a warning or alarm and otherwise adjust or maintain a current state of the proportional mixing valve. In this respect, it should be appreciated that the controller may have programmable logic capabilities to adjust or maintain multiple components of the disclosed system (e.g., proportional mixing valve, respective actuated valves on the solvent tank or LC container, pump speed, etc.) based on an output provided by one or more sensors. [00110] Measuring condition(s) of the diluted product may include measuring at least one of refractive index, density, viscosity, pH, mass flow, conductivity, or selective ion concentration of the final diluted product. In some embodiments, the step of measuring the condition of the final diluted product may include measuring a refractive index, a density, and a viscosity of the final diluted product. The step of modulating the proportional mixing valve may include maintaining a mixing ratio of water to liquid concentrate of about 10:1 to about 0.75:1. The step of modulating the proportional mixing valve may include maintaining a mixing ratio of water to liquid concentrate of about 2:1. The weight percent of the retardant salt compound relative to the total weight of the final diluted product is about 4% to about 30%, preferably about 5% to about 25%, more preferably about 6% to about 23%, and particularly about 7% to about 20%. The step of producing the final diluted product may include producing the final diluted product at a production rate of about 100 gallons per minute (gpm) to about 1200 gpm. The final diluted product may have a viscosity of about 150 cP to about 1500 cP, such as about 150 cP to about 400 cP, or about 401 cP to about 800 cP, or about 801 cP to about 1500 cP. The step of introducing the liquid concentrate into the proportional mixing valve may include pumping the liquid concentrate with a mechanical pump. The step of introducing the water into the proportional mixing valve may include pumping the water with a pump. Controlling modulation of the proportional mixing valve may include using the condition(s) measured as part of an automated feedback loop. Attorney Docket No. FFRS-012WO01 Example of Mixing System Operation with One Sensor [00111] As an example, a final diluted product or ready to use (RTU) long-term fire retardant is prepared by the following steps using a mixing system that includes a water source, a liquid concentrate source actuated valves on the outlets of the water source and liquid concentrate source, an actuated proportional mixing valve, a pump downstream of the proportional mixing valve, a refractive index sensor measuring the final diluted product downstream of the proportional mixing valve, and a controller that controls the actuated valves and the pump based on measurements from the refractive index sensor. [00112] First, power is provided to the mixing system and the mixing system’s controller runs through an automated start-up routine to check connectivity to and status of each of the components in the mixing system (e.g., sensors, pumps, variable frequency drivers, and valve actuating mechanisms). Once connectivity and component status are confirmed, then the controller provides a ready signal to the operator. The operator sets initial parameters based on the specific retardant that is being mixed and the desired flow rate into the RTU retardant storage tank and commands the mixing system to run. [00113] The controller adjusts the initial state of the proportional mixing valve to match the desired mixing ratio for the liquid concentrate. For example, if the mixing ratio for the liquid concentrate is 1 gallon of liquid concentrate to 2.4 gallons of water, then the controller adjusts the configuration of the proportional mixing valve to allow 2.4 times more water than liquid concentrate to pass through the proportional mixing valve. [00114] The controller sends signals to open the actuated valves on the water source and the liquid concentrate source. [00115] The controller ramps up the downstream pump to the desired production rate according to the rate input by the operator, which pulls water and liquid concentrate from their respective sources through the valves and pipes on their respective lines into the proportional mixing valve, combining the water and liquid concentrate at the desired ratio. The combined fluids travel from the proportional mixing valve through a section of pipe into the downstream pump. The downstream pump helps homogenize the mixture of combined fluids before sending the final diluted product to the storage tank. [00116] As the final diluted product is transferred to the storage tank the final diluted product flows past the refractive index sensor and is measured. The refractive index sensor transmits Attorney Docket No. FFRS-012WO01 the measured refractive index values of the final diluted product to the controller where the measured values are compared to target values. [00117] If the controller determines that the measured refractive index of the final diluted product is within a target tolerance range that was entered by the operator, then the controller maintains all settings and continues to monitor the output readings of the refractive index sensor and operates until either the operator stops the system, a pre-set quantity of final diluted product has been produced, or the refractive index of the final diluted product that is being transferred to the storage tank is out of tolerance. [00118] If at any point during operation of the mixing system, the controller detects a refractive index value of the final diluted product that is outside of the target tolerance range, then the controller responds accordingly. For instance, if the refractive index value measured by the refractive index sensor is less than the target tolerance range, then the controller adjusts the proportional mixing valve such that more concentrate and less water is allowed to pass through the proportional mixing valve. If the refractive index value measured by the refractive index sensor is greater than the target tolerance range, then the controller adjusts the proportional mixing valve such that more water and less concentrate is allowed to pass through the proportional mixing valve. [00119] The controller adjusts the proportional mixing valve in small steps. After each small step, the controller pauses for enough time for the final diluted product combined in the new ratio to reach the refractive index sensor so that the refractive index sensor measures the final diluted product combined in the new ratio and transmits the measured refractive index values to the controller. [00120] If the controller’s step adjustment to the proportional mixing valve brings the refractive index of the final diluted product back into tolerance, then the controller maintains the new parameters until the system stops operating. The system may stop operating because the operator stops the mixing system, a pre-set quantity of final diluted product was produced, or the refractive index of the final diluted product that is being transferred to the storage tank is again out of tolerance. [00121] If the controller’s step adjustment to the proportional mixing valve does not bring the refractive index of the final diluted product back into tolerance, then the controller repeats the process of making another step adjustment of the proportional mixing valve as above. The controller repeats step adjustments of the proportional mixing valve until the refractive index Attorney Docket No. FFRS-012WO01 of the final diluted product is back within the tolerance range. If the controller is not able to bring the final diluted product back within the tolerance range with adjusts of the proportional mixing valve, then the controller may stop operation of the mixing system and send an error code to the operator. [00122] When the measured refractive index of the final diluted product is within the tolerance that was entered by the operator, the controller maintains all settings and continues to monitor the measurements of the refractive index sensor. The system operates until either the operator stops the system, a pre-set quantity of final diluted product has been produced, or the refractive index of the final diluted product that is being transferred to the storage tank is out of tolerance. Example of Mixing System Operation with Two Sensors [00123] As another example, a ready to use (RTU) final diluted product long-term fire retardant is prepared by the following steps using a mixing system that includes a water source, a liquid concentrate source actuated valves on the outlets of the water source and liquid concentrate source, an actuated proportional mixing valve, a pump downstream of the proportional mixing valve, a refractive index sensor measuring the final diluted product downstream of the proportional mixing valve, a density sensor measuring the final diluted product downstream of the proportional mixing valve, and a controller that controls the actuated valves and the pump based on measurements from the refractive index sensor and the additional sensors. [00124] First, power is provided to the mixing system and the mixing system’s controller runs through an automated start-up routine to check connectivity to and status of each of the components in the mixing system (e.g., sensors, pumps, variable frequency drivers, and valve actuating mechanisms). Once connectivity and component status are confirmed, then the controller provides a ready signal to the operator. The operator sets initial parameters based on the specific retardant that is being mixed and the desired flow rate into the RTU retardant storage tank and commands the mixing system to run. [00125] The controller adjusts the initial state of the proportional mixing valve to match the desired mixing ratio for the liquid concentrate. For example, if the mixing ratio for the liquid concentrate is 1 gallon of liquid concentrate to 2.4 gallons of water, then the controller adjusts the configuration of the proportional mixing valve to allow 2.4 times more water than liquid concentrate to pass through the proportional mixing valve. Attorney Docket No. FFRS-012WO01 [00126] The controller sends signals to open the actuated valves on the water source and the liquid concentrate source. [00127] The controller ramps up the downstream pump to the desired production rate according to the rate input by the operator, which pulls water and liquid concentrate from their respective sources through the valves and pipes in their respective upstream lines into the proportional mixing valve, combining the water and liquid concentrate at the desired ratio. The combined fluids travel from the proportional mixing valve through a section of pipe into the downstream pump. The downstream pump helps homogenize the mixture of combined fluids before sending final diluted product to the storage tank. [00128] As the final diluted product is transferred to the storage tank the final diluted product flows past the refractive index sensor and the density sensor and is measured by the sensors. The refractive index sensor and the density sensor transmit the measured sensor values of the final diluted product to the controller where the measured values are compared to target values. [00129] If the controller determines that the measured refractive index and density of the final diluted product are within target tolerance ranges that were entered by the operator, then the controller maintains all settings and continues to operate the mixing system until operation stops. The controller continues to monitor the output readings of the refractive index sensor and the density sensor and operate accordingly. [00130] If at any point the controller determines that one of the sensors is out of the target tolerance range, then the controller responds in one of several ways described below. [00131] The refractive index sensor and the density sensor are set up as warning sensors and/or alarm and correct sensors. In some instances, one or both sensors are designated as both warning and alarm/correct sensors, where sensor measurements in a range close to but outside the target tolerance range raise a warning and sensor measurements in a range farther outside the target tolerance range raises an alarm/correct operation. In some instances, one sensor acts as a warning sensor and the other sensor acts as an alarm/correct sensor. [00132] For example, if the density sensor is designated as a warning sensor and the refractive index sensor is designated as an alarm/correct sensor, then when the measured refractive index is within tolerance, but the measured density is not, the controller may send warnings to the operator but not change any parameters of the mixing system. The mixing system continues to run with the same parameters until either the density is back within Attorney Docket No. FFRS-012WO01 specification, the density meets an alarm/correct state, or the mixing system finishes operation (e.g., produces a specified amount of final diluted product). If the controller determines that the measured refractive index is outside the target tolerance range, whether or not the density is within its tolerance range, then the controller adjusts the proportional mixing valve accordingly. If the controller detects that both the measured refractive index and density are out of their target tolerance ranges, the controller will determine if the density and refractive index are below or above the desired target. If both the density and refractive index are above their target tolerance ranges, then the controller adjusts the proportional mixing valve such that less concentrate and more water is allowed to pass through the proportional mixing valve. If both the density and refractive index are below their target tolerance ranges, then the controller adjusts the proportional mixing valve such that more concentrate and less water is allowed to pass through the proportional mixing valve. If the controller detects that one sensor metric is above its target tolerance range and another sensor metric is below its target tolerance range, then the controller may shut down the mixing system and alert the operator. [00133] The controller makes the adjustments described above in small steps allowing for enough time after each step adjustment for the final diluted product mixed at the new ratio to reach the refractive index sensor and the density sensor and to transmit the measured refractive index and density to the controller. If the adjustments made to the mixing ratio bring the sensor output of the final diluted product back into tolerance, the controller maintains the parameters until either the operator stops the system, a pre-set quantity of final diluted product is produced, or the final diluted product that is being transferred to the storage tank is again out of tolerance. If the measured refractive index or density is still out of tolerance, the controller will repeat the process of step adjustments to the proportional mixing valve until the refractive index and/or the density of the final diluted product transferred to the storage tank is within tolerance. [00134] FIG.3 illustrates a method 300 for providing a ready-to-use (RTU) fire retardant product for loading onto an aircraft, the RTU fire retardant product containing at least one fire retardant compound in accordance with the present technology. Method 300 may include blocks 310-330. [00135] Block 310 may include step 310A: operating at least one pump to flow water from a solvent tank, and flow a liquid concentrate (LC) fire retardant containing the at least one fire retardant compound from a liquid concentrate (LC) container, through a single automated Attorney Docket No. FFRS-012WO01 proportional mixing valve to form the RTU fire retardant product, wherein: an LC head pressure of the LC fire retardant in the LC container changes during step 310A; and the RTU fire retardant product is pumped through at least one conduit coupled between the single automated proportional mixing valve and a flow meter associated with the aircraft at a flow rate in a range of from 200 gallons/minute to 1000 gallons/minute. [00136] The LC fire retardant may have a viscosity in a range from between 1500 cP and 3000 cP. The at least one fire retardant compound may include at least one of magnesium chloride, ammonium phosphate, or polyphosphate. During block 310, a solvent head pressure of the solvent in the solvent tank may be maintained essentially constant. [00137] Prior to block 310, method 300 may include receiving first user input via a user interface. The first user input may relate to a target mix ratio for the water or other suitable solvent and the LC fire retardant to form the RTU fire retardant product. Method 300 may further include, prior to block 310, adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. [00138] The solvent tank may include a first actuated valve at an outlet of the solvent tank. The LC container may include a second actuated valve at an outlet of the LC container, and method 300 further includes, prior to block 310, automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. [00139] Method 300 may further include, prior to block 310, receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product. Block 310 may then further include operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. [00140] Method 300 may further include, prior to block 310, receiving third user input, via the user interface, relating to the range of the target refractive index for the RTU fire retardant product. [00141] Block 320 may include automatically and repeatedly measuring an in-line refractive index of the RTU fire retardant product, via an in-line refractometer disposed in the at least one conduit between the single automated proportional mixing valve and the flow meter Attorney Docket No. FFRS-012WO01 associated with the aircraft, as the RTU fire retardant product is pumped through the at least one conduit so as to generate a plurality of refractive index measurements for the RTU fire retardant product. [00142] Block 320 may further include storing a digital record of at least some of the plurality of refractive index measurements. [00143] Block 320 may further include automatically and repeatedly measuring the in-line refractive index of the RTU fire retardant product, via the in-line refractometer disposed in the at least one conduit between the single automated proportional mixing valve and the flow meter associated with the aircraft, as the RTU fire retardant product is pumped through the at least one conduit so as to generate the plurality of refractive index measurements for the RTU fire retardant product. [00144] Block 320 may further include automatically and repeatedly measuring an in-line density of the RTU fire retardant product, via the flow meter associated with the aircraft, as the RTU fire retardant product is pumped through the at least one conduit so as to generate a plurality of density measurements for the RTU fire retardant product. [00145] Block 330 may include step 330C automatically adjusting or maintaining at least one flow variable for each of the LC fire retardant and the water via operation of the single automated proportional mixing valve, based at least in part on the plurality of refractive index measurements generated in step 320B, to achieve a target refractive index of the RTU fire retardant product in a range of from 8 to 30 on the 10440 VP arbitrary scale. [00146] In block 330, a target weight percent of the at least one fire retardant compound in the RTU fire retardant product may be in a range of from 8% to 12%. The target refractive index of the RTU fire retardant product may be in a range of from 8.5 to 20.0 on the 10440 VP arbitrary scale. [00147] In block 330, step 330C may be performed after the flow rate of the RTU fire retardant product is at the target flow rate. [00148] In block 330, step 330C may further include step 330C1: at a first time, comparing a first refractive index measurement of the plurality of refractive index measurements generated in B) with the range for the target refractive index of the RTU fire retardant product. Attorney Docket No. FFRS-012WO01 [00149] In block 330, step 330C may further include step 330C2: if the first refractive index measurement of the RTU fire retardant product is within the range for the target refractive index of the RTU fire retardant product, maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. [00150] In block 330, step 330C may further include step 330C3: if the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product, adjusting the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. If the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product, step 330C3 may include operating the single automated proportional mixing valve so as to adjust the at least one flow variable for each of the LC fire retardant and the water such that in step 320B, the in-line refractive index of the RTU fire retardant product changes by approximately 0.1 on the 10440 VP arbitrary scale. [00151] In block 330, step 330C may further include step 330C4: stopping the at least one pump in A) if fourth user input is received via the user interface relating to stopping operation of the at least one pump. step 330C may further include step 330C5 stopping the at least one pump in step 310A if fifth user input relating to a pre-set quantity of the RTU fire retardant product is received via the user interface and an amount of the RTU fire retardant product pumped through the at least one conduit equals, approximately equals, or exceeds the pre-set quantity of the RTU fire retardant product. [00152] In block 330, step 330C may further include step 330C6 repeating step 330C1 and step 330C2 or step 330C3 at a second time using a second refractive index measurement of the plurality of refractive index measurements. [00153] In block 330, step 330C6 may further include step 330C6a: waiting a predetermined time period following step 330C3. step 330C6 may further include step 330C6b: after waiting the predetermined time period, repeating step 330C1 and step 330C2 or step 330C3 at a second time using a second refractive index measurement of the plurality of refractive index measurements. [00154] In block 330, step 330C may further include automatically adjusting or maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the plurality of refractive index Attorney Docket No. FFRS-012WO01 measurements generated in step 320B1 and the plurality of density measurements generated in step 320B2, to achieve the target refractive index of the RTU fire retardant product in the range of from 8 to 30 on the 10440 VP arbitrary scale. [00155] FIG.4 illustrates a method 400 of providing a ready-to-use (RTU) fire retardant product containing at least one retardant compound. Method 400 may include blocks 410- 430. [00156] Block 410 may include step 410A of forming the RTU fire retardant product by creating a mixture of water and a liquid concentrate (LC) fire retardant containing the at least one retardant compound, wherein the LC fire retardant has a viscosity in a range of from between 1500 centipoise (cP) and 3000 cP. [00157] Block 420 may include step 420B of measuring at least one parameter representing a concentration of the at least one retardant compound in the mixture. [00158] Block 430 may include step 430C of automatically adjusting at least one flow variable for each of the LC fire retardant and the water based at least in part on step 420B, to achieve a target weight percent of the at least one retardant compound in the RTU fire retardant product in a range of from 8% to 12% and achieve a flow rate for the RTU fire retardant product in a range of from 200 gallons/minute to 1000 gallons/minute. [00159] FIG.5 illustrates a method 500 of providing a ready-to-use (RTU) fire retardant product containing at least one retardant compound. Method 500 may include blocks 510- 530. [00160] Block 510 may include step 510A of forming the RTU fire retardant product by creating a mixture of water and a liquid concentrate (LC) fire retardant containing the at least one retardant compound, wherein the LC fire retardant has a viscosity in a range of from between 1500 centipoise (cP) and 3000 cP and a head pressure of the LC fire retardant changes over time. [00161] Block 520 may include step 520B of measuring a refractive index of the mixture. [00162] Block 530 may include step 530C of automatically adjusting at least one flow variable for each of the LC fire retardant and the water based at least in part on step 520B, to achieve a target refractive index in a range of from 8.5 to 20.0 on the 10440 VP arbitrary scale and achieve a flow rate for the RTU fire retardant product in a range of from 200 gallons/minute to 1000 gallons/minute. Attorney Docket No. FFRS-012WO01 Conclusion [00163] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize or be able to ascertain, using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. [00164] Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. [00165] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. [00166] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” [00167] The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are Attorney Docket No. FFRS-012WO01 conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and/or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. [00168] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law. [00169] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, Attorney Docket No. FFRS-012WO01 optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. [00170] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

Attorney Docket No. FFRS-012WO01 CLAIMS 1. A mix plant for providing a ready-to-use (RTU) fire retardant product containing at least one fire retardant compound for loading onto an aircraft, the mix plant comprising: a water tank to hold water; a liquid concentrate (LC) container to hold a liquid concentrate (LC) fire retardant containing the at least one fire retardant compound, wherein an LC head pressure of the LC fire retardant in the LC container changes as the LC fire retardant is consumed to provide the RTU fire retardant product; a single automated proportional mixing valve, fluidically coupled to the water tank and the LC container, to mix the water and the LC fire retardant and thereby form the RTU fire retardant product; at least one conduit, fluidically coupled to the single automated proportional mixing valve and a flow meter, to carry the RTU fire retardant product from the single automated proportional mixing valve; at least one pump, fluidically coupled to the at least one conduit, to pump the RTU fire retardant product through the at least one conduit; an in-line refractometer, positioned in the at least one conduit between the single automated proportional mixing valve and the flow meter so as to be in fluidic contact with the RTU fire retardant product, to measure an in-line refractive index of the RTU fire retardant product in the at least one conduit; and at least one controller, communicatively coupled to the in-line refractometer and the single automated proportional mixing valve, to automatically adjust at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the in-line refractive index measured by the in-line refractometer, to achieve a target refractive index of the RTU fire retardant product in a range of from 10 to 30 on the 10440 VP arbitrary scale. 2. The mix plant of claim 1, wherein the water tank comprises a water level sensor to automatically refill the water tank with additional water as the water is consumed to provide the RTU fire retardant product so as to maintain an essentially constant water head pressure at an outlet of the water tank. Attorney Docket No. FFRS-012WO01 3. The mix plant of claim 1, further comprising: a first actuated valve coupled to an outlet of the water tank and communicatively coupled to the at least one controller, wherein the first actuated valve is responsive to a first signal output by the at least one controller to open and close the first actuated valve; and a second actuated valve coupled to an outlet of the LC container and communicatively coupled to the at least one controller, wherein the second actuated valve is responsive to a second signal output by the at least one controller to open and close the second actuated valve. 4. The mix plant of claim 2, further comprising: a first actuated valve coupled to an outlet of the water tank and communicatively coupled to the at least one controller, wherein the first actuated valve is responsive to a first signal output by the at least one controller to open and close the first actuated valve; and a second actuated valve coupled to an outlet of the LC container and communicatively coupled to the at least one controller, wherein the second actuated valve is responsive to a second signal output by the at least one controller to open and close the second actuated valve. 5. The mix plant of claim 2, wherein: the at least one pump is communicatively coupled to the at least one controller and is responsive to at least one pump control signal output by the at least one controller to control a flow rate of the at least one pump. 6. The mix plant of claim 3, wherein: the at least one pump is communicatively coupled to the at least one controller and is responsive to at least one pump control signal output by the at least one controller to control a flow rate of the at least one pump. 7. The mix plant of claim 1, further comprising the flow meter, wherein: the at least one controller is communicatively coupled to the in-line refractometer, the flow meter and the single automated proportional mixing valve, to automatically adjust the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the in-line refractive index measured by the in-line refractometer and an in-line density of the RTU fire retardant product Attorney Docket No. FFRS-012WO01 measured by the flow meter, to achieve a target refractive index of the RTU fire retardant product in a range of from 8 to 30 on the 10440 VP arbitrary scale. 8. The mix plant of claim 2, further comprising the flow meter, wherein: the at least one controller is communicatively coupled to the in-line refractometer, the flow meter and the single automated proportional mixing valve, to automatically adjust the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the in-line refractive index measured by the in-line refractometer and an in-line density of the RTU fire retardant product measured by the flow meter, to achieve a target refractive index of the RTU fire retardant product in a range of from 8 to 30 on the 10440 VP arbitrary scale. 9. The mix plant of claim 3, further comprising the flow meter, wherein: the at least one controller is communicatively coupled to the in-line refractometer, the flow meter and the single automated proportional mixing valve, to automatically adjust the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the in-line refractive index measured by the in-line refractometer and an in-line density of the RTU fire retardant product measured by the flow meter, to achieve a target refractive index of the RTU fire retardant product in a range of from 8 to 30 on the 10440 VP arbitrary scale. 10. The mix plant of claim 5, further comprising the flow meter, wherein: the at least one controller is communicatively coupled to the in-line refractometer, the flow meter and the single automated proportional mixing valve, to automatically adjust the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the in-line refractive index measured by the in-line refractometer and an in-line density of the RTU fire retardant product measured by the flow meter, to achieve a target refractive index of the RTU fire retardant product in a range of from 8 to 30 on the 10440 VP arbitrary scale. 11. A method of providing a ready-to-use (RTU) fire retardant product containing at least one retardant compound, the method comprising: Attorney Docket No. FFRS-012WO01 A) forming the RTU fire retardant product by creating a mixture of water and a liquid concentrate (LC) fire retardant containing the at least one retardant compound, wherein the LC fire retardant has a viscosity in a range of from between 1500 centipoise (cP) and 3000 cP; B) measuring at least one parameter representing a concentration of the at least one retardant compound in the mixture; and C) automatically adjusting at least one flow variable for each of the LC fire retardant and the water based at least in part on B), to: achieve a target weight percent of the at least one retardant compound in the RTU fire retardant product in a range of from 8% to 12%; and achieve a flow rate for the RTU fire retardant product in a range of from 200 gallons/minute to 1000 gallons/minute. 12. A method of providing a ready-to-use (RTU) fire retardant product containing at least one retardant compound, the method comprising: A) forming the RTU fire retardant product by creating a mixture of water and a liquid concentrate (LC) fire retardant containing the at least one retardant compound, wherein: the LC fire retardant has a viscosity in a range of from between 1500 centipoise (cP) and 3000 cP; and a head pressure of the LC fire retardant changes over time; B) measuring a refractive index of the mixture; and C) automatically adjusting at least one flow variable for each of the LC fire retardant and the water based at least in part on B), to: achieve a target refractive index in a range of from 8.5 to 20.0 on the 10440 VP arbitrary scale; and achieve a flow rate for the RTU fire retardant product in a range of from 200 gallons/minute to 1000 gallons/minute. 13. A method of providing a ready-to-use (RTU) fire retardant product for loading onto an aircraft, the RTU fire retardant product containing at least one fire retardant compound, the method comprising: A) operating at least one pump to flow water from a water tank, and flow a liquid concentrate (LC) fire retardant containing the at least one fire retardant compound from a Attorney Docket No. FFRS-012WO01 liquid concentrate (LC) container, through a single automated proportional mixing valve to form the RTU fire retardant product, wherein: an LC head pressure of the LC fire retardant in the LC container changes during A); and the RTU fire retardant product is pumped through at least one conduit coupled between the single automated proportional mixing valve and a flow meter associated with the aircraft at a flow rate in a range of from 200 gallons/minute to 1000 gallons/minute; B) automatically and repeatedly measuring an in-line refractive index of the RTU fire retardant product, via an in-line refractometer disposed in the at least one conduit between the single automated proportional mixing valve and the flow meter associated with the aircraft, as the RTU fire retardant product is pumped through the at least one conduit so as to generate a plurality of refractive index measurements for the RTU fire retardant product; and C) automatically adjusting or maintaining at least one flow variable for each of the LC fire retardant and the water via operation of the single automated proportional mixing valve, based at least in part on the plurality of refractive index measurements generated in B), to achieve a target refractive index of the RTU fire retardant product in a range of from 8 to 30 on the 10440 VP arbitrary scale. 14. The method of claim 13, wherein the LC fire retardant has a viscosity in a range of from between 1500 centipoise (cP) and 3000 cP. 15. The method of claim 13, wherein in C), a target weight percent of the at least one fire retardant compound in the RTU fire retardant product is in a range of from 8% to 12%. 16. The method of claim 13, wherein in C), the target refractive index of the RTU fire retardant product is in a range of from 8.5 to 20.0 on the 10440 VP arbitrary scale. 17. The method of claim 15, wherein in C), the target refractive index of the RTU fire retardant product is in a range of from 8.5 to 20.0 on the 10440 VP arbitrary scale. 18. The method of claim 13, wherein the at least one fire retardant compound comprises at least one of magnesium chloride, ammonium phosphate, or polyphosphate. Attorney Docket No. FFRS-012WO01 19. The method of claim 14, wherein the at least one fire retardant compound comprises at least one of magnesium chloride, ammonium phosphate, or polyphosphate. 20. The method of claim 15, wherein the at least one fire retardant compound comprises at least one of magnesium chloride, ammonium phosphate, or polyphosphate. 21. The method of claim 16, wherein the at least one fire retardant compound comprises at least one of magnesium chloride, ammonium phosphate, or polyphosphate. 22. The method of claim 17, wherein the at least one fire retardant compound comprises at least one of magnesium chloride, ammonium phosphate, or polyphosphate. 23. The method of claim 13, wherein A) further comprises: maintaining a water head pressure of the water in the water tank essentially constant during A). 24. The method of claim 14, wherein A) further comprises: maintaining a water head pressure of the water in the water tank essentially constant during A). 25. The method of claim 15, wherein A) further comprises: maintaining a water head pressure of the water in the water tank essentially constant during A). 26. The method of claim 16, wherein A) further comprises: maintaining a water head pressure of the water in the water tank essentially constant during A). 27. The method of claim 17, wherein A) further comprises: maintaining a water head pressure of the water in the water tank essentially constant during A). Attorney Docket No. FFRS-012WO01 28. The method of claim 18, wherein A) further comprises: maintaining a water head pressure of the water in the water tank essentially constant during A). 29. The method of claim 13, further comprising: storing a digital record of at least some of the plurality of refractive index measurements generated in B). 30. The method of claim 14, further comprising: storing a digital record of at least some of the plurality of refractive index measurements generated in B). 31. The method of claim 15, further comprising: storing a digital record of at least some of the plurality of refractive index measurements generated in B). 32. The method of claim 16, further comprising: storing a digital record of at least some of the plurality of refractive index measurements generated in B). 33. The method of claim 17, further comprising: storing a digital record of at least some of the plurality of refractive index measurements generated in B). 34. The method of claim 18, further comprising: storing a digital record of at least some of the plurality of refractive index measurements generated in B). 35. The method of claim 23, further comprising: storing a digital record of at least some of the plurality of refractive index measurements generated in B). Attorney Docket No. FFRS-012WO01 36. The method of claim 13, further comprising, prior to A): receiving first user input, via a user interface, relating to a target mix ratio for the water and the LC fire retardant to form the RTU fire retardant product; and adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 37. The method of claim 14, further comprising, prior to A): receiving first user input, via a user interface, relating to a target mix ratio for the water and the LC fire retardant to form the RTU fire retardant product; and adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 38. The method of claim 15, further comprising, prior to A): receiving first user input, via a user interface, relating to a target mix ratio for the water and the LC fire retardant to form the RTU fire retardant product; and adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 39. The method of claim 16, further comprising, prior to A): receiving first user input, via a user interface, relating to a target mix ratio for the water and the LC fire retardant to form the RTU fire retardant product; and adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 40. The method of claim 17, further comprising, prior to A): receiving first user input, via a user interface, relating to a target mix ratio for the water and the LC fire retardant to form the RTU fire retardant product; and adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. Attorney Docket No. FFRS-012WO01 41. The method of claim 18, further comprising, prior to A): receiving first user input, via a user interface, relating to a target mix ratio for the water and the LC fire retardant to form the RTU fire retardant product; and adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 42. The method of claim 23, further comprising, prior to A): receiving first user input, via a user interface, relating to a target mix ratio for the water and the LC fire retardant to form the RTU fire retardant product; and adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 43. The method of claim 29, further comprising, prior to A): receiving first user input, via a user interface, relating to a target mix ratio for the water and the LC fire retardant to form the RTU fire retardant product; and adjusting an initial state of the single automated proportional mixing valve based at least in part on the target mix ratio so as to initially set the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 44. The method of claim 36, wherein the water tank includes a first actuated valve at an outlet of the water tank, the LC container includes a second actuated valve at an outlet of the LC container, and the method further comprises, prior to A): automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. 45. The method of claim 37, wherein the water tank includes a first actuated valve at an outlet of the water tank, the LC container includes a second actuated valve at an outlet of the LC container, and the method further comprises, prior to A): automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. Attorney Docket No. FFRS-012WO01 46. The method of claim 38, wherein the water tank includes a first actuated valve at an outlet of the water tank, the LC container includes a second actuated valve at an outlet of the LC container, and the method further comprises, prior to A): automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. 47. The method of claim 39, wherein the water tank includes a first actuated valve at an outlet of the water tank, the LC container includes a second actuated valve at an outlet of the LC container, and the method further comprises, prior to A): automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. 48. The method of claim 40, wherein the water tank includes a first actuated valve at an outlet of the water tank, the LC container includes a second actuated valve at an outlet of the LC container, and the method further comprises, prior to A): automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. 49. The method of claim 41, wherein the water tank includes a first actuated valve at an outlet of the water tank, the LC container includes a second actuated valve at an outlet of the LC container, and the method further comprises, prior to A): automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. 50. The method of claim 42, wherein the water tank includes a first actuated valve at an outlet of the water tank, the LC container includes a second actuated valve at an outlet of the LC container, and the method further comprises, prior to A): automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. 51. The method of claim 43, wherein the water tank includes a first actuated valve at an outlet of the water tank, the LC container includes a second actuated valve at an outlet of the LC container, and the method further comprises, prior to A): Attorney Docket No. FFRS-012WO01 automatically opening the first actuated valve and the second actuated valve after adjusting the initial state of the single automated proportional mixing valve. 52. The method of claim 36, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 53. The method of claim 37, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 54. The method of claim 38, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 55. The method of claim 39, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 56. The method of claim 40, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and Attorney Docket No. FFRS-012WO01 in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 57. The method of claim 41, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 58. The method of claim 42, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 59. The method of claim 43, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 60. The method of claim 44, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. Attorney Docket No. FFRS-012WO01 61. The method of claim 45, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 62. The method of claim 46, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 63. The method of claim 47, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 64. The method of claim 48, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. 65. The method of claim 49, further comprising: prior to A), receiving second user input, via the user interface, relating to a target flow rate for the RTU fire retardant product; and in A), operating the at least one pump so as to gradually increase the flow rate of the RTU fire retardant product to the target flow rate and thereby pull the water and the LC fire retardant through the single automated proportional mixing valve. Attorney Docket No. FFRS-012WO01 66. The method of claim 36, wherein in C) is performed after the flow rate of the RTU fire retardant product is at the target flow rate. 67. The method of claim 44, wherein in C) is performed after the flow rate of the RTU fire retardant product is at the target flow rate. 68. The method of claim 52, wherein in C) is performed after the flow rate of the RTU fire retardant product is at the target flow rate. 69. The method of claim 36, further comprising, prior to A): receiving third user input, via the user interface, relating to the range of the target refractive index for the RTU fire retardant product. 70. The method of claim 44, further comprising, prior to A): receiving third user input, via the user interface, relating to the range of the target refractive index for the RTU fire retardant product. 71. The method of claim 52, further comprising, prior to A): receiving third user input, via the user interface, relating to the range of the target refractive index for the RTU fire retardant product. 72. The method of claim 66, further comprising, prior to A): receiving third user input, via the user interface, relating to the range of the target refractive index for the RTU fire retardant product. 73. The method of claim 13, wherein C) further comprises: C1) at a first time, comparing a first refractive index measurement of the plurality of refractive index measurements generated in B) with the range for the target refractive index of the RTU fire retardant product; C2) if the first refractive index measurement of the RTU fire retardant product is within the range for the target refractive index of the RTU fire retardant product, maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve; and Attorney Docket No. FFRS-012WO01 C3) if the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product, adjusting the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 74. The method of claim 36, wherein C) further comprises: C1) at a first time, comparing a first refractive index measurement of the plurality of refractive index measurements generated in B) with the range for the target refractive index of the RTU fire retardant product; C2) if the first refractive index measurement of the RTU fire retardant product is within the range for the target refractive index of the RTU fire retardant product, maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve; and C3) if the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product, adjusting the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 75. The method of claim 52, wherein C) further comprises: C1) at a first time, comparing a first refractive index measurement of the plurality of refractive index measurements generated in B) with the range for the target refractive index of the RTU fire retardant product; C2) if the first refractive index measurement of the RTU fire retardant product is within the range for the target refractive index of the RTU fire retardant product, maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve; and C3) if the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product, adjusting the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. Attorney Docket No. FFRS-012WO01 76. The method of claim 66, wherein C) further comprises: C1) at a first time, comparing a first refractive index measurement of the plurality of refractive index measurements generated in B) with the range for the target refractive index of the RTU fire retardant product; C2) if the first refractive index measurement of the RTU fire retardant product is within the range for the target refractive index of the RTU fire retardant product, maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve; and C3) if the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product, adjusting the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 77. The method of claim 69, wherein C) further comprises: C1) at a first time, comparing a first refractive index measurement of the plurality of refractive index measurements generated in B) with the range for the target refractive index of the RTU fire retardant product; C2) if the first refractive index measurement of the RTU fire retardant product is within the range for the target refractive index of the RTU fire retardant product, maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve; and C3) if the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product, adjusting the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve. 78. The method of claim 69, wherein C) further comprises: C4) stopping the at least one pump in A) if fourth user input is received via the user interface relating to stopping operation of the at least one pump; and C5) stopping the at least one pump in A) if: fifth user input relating to a pre-set quantity of the RTU fire retardant product is received via the user interface; and Attorney Docket No. FFRS-012WO01 an amount of the RTU fire retardant product pumped through the at least one conduit equals, approximately equals, or exceeds the pre-set quantity of the RTU fire retardant product. 79. The method of claim 73, wherein C) further comprises: C4) stopping the at least one pump in A) if fourth user input is received via a user interface relating to stopping operation of the at least one pump; and C5) stopping the at least one pump in A) if: fifth user input relating to a pre-set quantity of the RTU fire retardant product is received via the user interface; and an amount of the RTU fire retardant product pumped through the at least one conduit equals, approximately equals, or exceeds the pre-set quantity of the RTU fire retardant product. 80. The method of claim 73, further comprising: C6) repeating C1) and either C2) or C3) at a second time using a second refractive index measurement of the plurality of refractive index measurements. 81. The method of claim 80, wherein: the first refractive index measurement of the RTU fire retardant product is not within the range for the target refractive index of the RTU fire retardant product; and C3) comprises: operating the single automated proportional mixing valve so as to adjust the at least one flow variable for each of the LC fire retardant and the water such that in B), the in-line refractive index of the RTU fire retardant product changes by approximately 0.1 on the 10440 VP arbitrary scale. 82. The method of claim 81, wherein C6) comprises: C6a) waiting a predetermined time period following C3); and C6b) after waiting the predetermined time period, repeating C1) and either C2) or C3) at a second time using a second refractive index measurement of the plurality of refractive index measurements. Attorney Docket No. FFRS-012WO01 83. The method of claim 13, wherein: B) comprises: B1) automatically and repeatedly measuring the in-line refractive index of the RTU fire retardant product, via the in-line refractometer disposed in the at least one conduit between the single automated proportional mixing valve and the flow meter associated with the aircraft, as the RTU fire retardant product is pumped through the at least one conduit so as to generate the plurality of refractive index measurements for the RTU fire retardant product; and B2) automatically and repeatedly measuring an in-line density of the RTU fire retardant product, via the flow meter associated with the aircraft, as the RTU fire retardant product is pumped through the at least one conduit so as to generate a plurality of density measurements for the RTU fire retardant product; and C) comprises: automatically adjusting or maintaining the at least one flow variable for each of the LC fire retardant and the water via the single automated proportional mixing valve, based at least in part on the plurality of refractive index measurements generated in B1) and the plurality of density measurements generated in B2, to achieve the target refractive index of the RTU fire retardant product in the range of from 8 to 30 on the 10440 VP arbitrary scale.