EP0241169A1

EP0241169A1 - Improved breathing apparatus

Info

Publication number: EP0241169A1
Application number: EP87302408A
Authority: EP
Inventors: John Delwyn Evans; Gordon Smith; Gordon Allan Johnston
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1986-04-02
Filing date: 1987-03-20
Publication date: 1987-10-14
Also published as: GB2188553A; ZA872153B; GB8608057D0; AU7067487A

Abstract

A breathing apparatus providing security of oxygen supply in use and with the potential for a long duration comprises personal gas supply means (10,11,12) connected to a canister, 3, containing a substance generating oxygen on reaction with carbon dioxide and moisture in a wearer's exhalations. A bottle of compressed oxygen, 6, doses oxygen into the breathing circuit when required by the wearer.

Description

This invention concerns an improved breathing apparatus, more especially it concerns a closed circuit breathing apparatus having dual sources of oxygen.
Closed circuit apparatus for use in hazardous atmospheres for escape and rescue purposes are well known, and may be of a variety of types. It is to be noted that such apparatus are not suitable for use under water, although they may be briefly submerged. Apparatus intended for rescue work, for example in underground mines, principally comprise a compressed oxygen bottled and a carbon dioxide absorber, invariably a canister containing soda-lime, together with a breathing bag and breathing tubes, and valves to ensure one-way flow and to prevent overpressurising the system. Oxygen may be supplied into the breathing circuit by a constant flow valve, a demand valve or a combination of a constant flow valve and a demand valve. Carbon dioxide is present in the exhalations from the user of the apparatus, and to prevent accumulation of CO₂ in the breathing gas, the exhalations are passed through soda-lime, which absorbs CO₂. The chemical reaction during absorption heats up the purified gas and also produces water vapour, necessitating careful design and/or coolers of various types in order to provide breathing gas at an acceptable temperature. Open circuit apparatus vent exhalations to the atmosphere, so that no purification is required. Compressed oxygen or compressed air open circuit breathing apparatus are widely used also, for example by fire brigades, but the venting of exhalations results in a high usage rate of gas and a relatively short life because of weight limitations if the apparatus is to be man portable on land.
In certain environments, such as in coal mines and generally in the chemical and petroleum industries, it may be necessary for a worker to escape from a suffocating, toxic or explosive atmosphere, to a safer environment. A variety of short duration escape apparatus have been produced under the name of "self-rescuers" or "self-rescue sets". In their simplest forms they may comprise a canister of catalyst to convert carbon monoxide to non toxic carbon dioxide for use in coal mines, or a small, cylinder of compressed air providing a miniature open circuit set eg 200 l of air at 200 bar pressure will provide a duration of 8 minutes. As an alternative to compressed gas escape apparatus, the "chemical oxygen" escape sets have become established, using an alkali metal oxide which generates oxygen upon exposure to the carbon dioxide and moisture in a user's exhalation. Chemical oxygen sets, however, suffer from the disadvantage that insufficient oxygen is available immediately upon donning the apparatus, and this has led to the use of "starter candles", which provide a few minutes of oxygen generation by a chemical reaction independent of a user's exhalations, or by the provision of a small cylinder containing 5 litres of oxygen which is turned on immediately; both rapidly fill the breathing bag to allow the wearer a breathable gas in sufficient quantity. The use of small oxygen bottles as starters is illustrated in French Patent No. 1,349,411 (Fenzy) and GB 828,406 (MSA).
The present invention aims to satisfy several requirements; to provide sufficient oxygen to sustain life for a set duration, and be flexible in principle to permit durations for example of 30,60,120 or 180 minutes; to provide a sufficient volume of oxygen at low breathing volumes, for example a "rest" situation, at 10 l/min and also at high breathing volumes, for example an "escape" situation involving hard physical effort such as climbing inside an oil platform leg, at 100 l/min; to maintain the temperature and condition of inspired oxygen at physiologically acceptable levels; to remove carbon dioxide from exhalations so that the concentration of carbon dioxide in the inspired oxygen does not exceed acceptable levels; and to maintain inhalation and exhalation breathing resistances within acceptable levels throughout the wearing period.
The present invention provides a breathing apparatus usable as a closed circuit breathing apparatus and comprising a personal gas supply means for inhalation and exhalation, a canister connected to receive the exhalations of a wearer and containing a charge of a substance capable of generating oxygen upon reaction with the carbon dioxide and moisture in the exhalations, a breathing bag connected to the canister to receive oxygen and purified exhalations and a cylinder of compressed oxygen having a dosing valve actuated by the requirements of the wearer and adapted to feed into the breathing circuit, suitably between the canister and the wearer.
In its simplest embodiment, the personal gas supply means may comprise a single breathing hose through which inhalations and exhalations pass, and also the canister may permit tidal (pendulum) flow therethrough. In other embodiments, there are provided inhalation and exhalation hoses, which are desirably fitted with one-way valves to direct gas flow in the appropriate direction; such valves may be at either end of the hoses, or may be incorporated in a mouthpiece fitting or a half- or full-face mask.
The substance capable of generating oxygen is preferably an alkali metal superoxide or mixed superoxides. It is preferred to use potassium superoxide (KO₂) which has a greater bound oxygen content per unit weight than sodium superoxide. The use of such a substance has significant advantages in addition to the generation of oxygen in that not only is carbon dioxide absorbed but also water vapour reacts and is removed from the circulating breathing gas. This is to be contrasted with the usual carbon dioxide absorber, soda lime, which releases water vapour as a reaction product into the breathing gas. In conventional closed circuit oxygen breathing apparatus, the circulating breathing gas is saturated with water vapour with the result that the temperature of the gas is of great importance since the physiological tolerance temperature of saturated air is approximately 53°C, whereas for dry air the tolerance temperature is 91°C. In a conventional apparatus, purified exhalations leaving the soda lime canister are at temperatures of 50-60°C, so that artificial cooling means or large surface areas for cooling are necessary. In the apparatus of the present invention much higher temperatures can be tolerated by the use without significant discomfort. Nonetheless, the apparatus may incorporate cooling means for gas to be inhaled. Many cooling means have been suggested and used in the art of conventional breathing apparatus, including heat exchangers, ice or dry-ice containers, evaporative coolers and forced air cooling using an electric fan, which latter is preferred for use in the present invention.
It will be recognised that known breathing apparatus of this type do not have two separate sources of oxygen available to a wearer throughout the nominal duration of the apparatus. The quantities of oxygen-generating substance and the compressed oxygen volume and cylinder size are selected to provide an oxygen supply from the substance of 1 to 2 l/min, ie. sufficient for normal movement or rest, for a desired nominal duration and oxygen is available on demand and as required from the compressed oxygen cylinder up to the maximum requirements of the wearer, eg. to 100-120 l/min. In one embodiment of the present invention, a relatively low constant flow of oxygen (eg 1 to 2 l/min) is supplied from the cylinder in addition to the flow on demand. Suitable demand valves and constant flow/demand valves are available from commercial sources, and may be actuated by a reduction of pressure or by the emptying of the breathing bag.
The breathing bag may be a bladder or a metal-type breathing bag, and may be selected according to the intended use of the apparatus, and weight and durability requirements.
In a preferred embodiment, a vent-to-atmosphere valve is incorporated in the breathing circuit between the personal gas supply means and the canister and is positioned and adapted to release part of the exhaled breath to the atmosphere before it passes through the canister. Accordingly, the life of the oxygen-generating substance is prolonged and/or the quantity of substance may be reduced, reducing the volume and weight of the canister.
The apparatus of the invention offers primarily improved security and safety to the wearer compared to known apparatus, in that failure of one oxygen source, for whatever reason, does not affect the ability of the other source to provide sufficient oxygen to sustain life. Furthermore, it has been known for certain apparatus currently marketed to provide insufficient oxygen in tests on a treadmill so that the wearer would have lost consciousness or has been seriously weakened. The apparatus of the invention may also provide considerably extended duration which may be necessary while awaiting rescue.
The apparatus of the invention is illustrated in the accompanying schematic drawings in which Figs 1 and 2 depicit first and second embodiments.
Referring firstly to Fig 1, the apparatus has a metal breathing bag generally indicated by 1, and part of the bag is formed by a metal bulkhead, 2. Mounted on the bulkhead is a canister, 3, containing a charge of 2 kg KO₂ between dust filters (not shown). The canister has an inlet, 4, and an outlet, 5, which outlet is connected to the breathing bag. The bulkhead also carries a compressed oxygen bottle, 6, of capacity up to 1800 l at 200 bar pressure having a reducing valve and pressure gauge, 7, and having a line into the breathing bag in which is positioned a pressure operated demand valve, shown in outline, 8. From the breathing bag, an outlet connection piece, 9, having a one-way valve, is attached to an inhalation breathing hose, 10, leading to a mouthpiece, 11, and an exhalation by means of a valve body, 13, having a vent-to-atmosphere valve, 14, and, between the valve 14 and the inlet to the canister, a further one-way valve. A nose-clip, 15, is attachd by a cord to the mouthpiece. This embodiment of the apparatus is intended to be worn as a back pack and shoulder straps and a waist belt (not shown) are to be fitted.
In use, a wearer donning the apparatus inhales, causing, because of the one-way valves, a reduction of pressure within the breathing bag, and actuating the demand valve to dose fresh oxygen from the cylinder into the breathing bag to satisfy the immediate requirements of the wearer. Upon the wearer exhaling, the exhalations pass through hose 12 into the canister 3 where the carbon dioxide and water vapour in the exhalations react with the potassium superoxide to form potassium carbonate and potassium hydrogen carbonate and to release oxygen which fills the breathing bag in preparation for the next inhalation. As back pressure builds up in the canister and breathing bag, part of each exhalation is vented to the atmosphere through valve 14. Should the breathing bag at the next inhalation, or any inhalation caused by exertion for example, contain insufficient oxygen, the demand valve will operate to dose further oxygen into the breathing circuit.
A second embodiment of the invention is illustrated in Fig 2, to which reference is now made. A mouthpiece, 21 is connected by a single breathing tube, 22, to a valve unit containing an inhalation valve, 23, and an exhalation valve, 24. An oxygen cylinder, 25, carries a reducing and demand valve block having a pressure gauge 25a, the block being connected by a hose of pipe, 26, to the inhalation valve 24. Also connected to the hose or pipe is a breathing bag, 27, provided with an excess pressure valve, 28. The breathing bag has a further connection hose or pipe, 29, to one side of a KO₂ canister, 20. The canister is connected at its other side to the exhalation valve by a hose or pipe, 31, having an excess pressure valve, 32. A close circuit valve, 33, which is effective to open or close the connection hose or pipe 29 is fitted therein.
If the close circuit valve 33 is in the "open" position, the apparatus operates as a closed circuit apparatus with supplementary oxygen on demand, in analogous manner to the apparatus of Fig. 1. If, however, the valve 33 is closed, the apparatus operates as a short duration compressed oxygen open circuit apparatus. The wearer receives oxygen on demand from the cylinder; the user's exhalations are prevented from passing through the canister, and exhaust to the atmosphere through valve 32. It may be advantageous on occasion to operate in this manner, where the wearer receives only cool dry oxygen from the cylinder.

Claims

1. An escape or rescue breathing apparatus usable as a closed circuit apparatus and having a breathing circuit comprising a personal gas supply means for inhalation and exhalation, a purifier canister to remove carbon dioxide from exhalations, a counter-lung breathing bag and a source of compressed oxygen with a demand valve for dosing fresh oxygen into the circuit, characterised in that the purifier canister contains a charge of a substance capable of generating oxygen upon exposure to the carbon dioxide and moisture in the exhalations.

2. An apparatus according to claim 1, characterised in that the source of compressed oxygen is connected to the circuit between the canister and the wearer and on the inhalation side of the circuit.

3. An apparatus according to claim 1 or 2, characterised in that the demand valve has an associated constant flow valve capable of continuously feeding oxygen into the circuit.

4. An apparatus according to any one of the preceding claims, characterised in that the canister is arranged in the circuit to permit tidal flow therethrough.

5. An apparatus according to any one of the preceding claims, characterised in that the personal gas supply means has a single breathing hose.

6. An apparatus according to any one of the preceding claims, characterised in that the substance in the canister is potassium superoxide.