GB2063536A - Pneumatic fire alarm system - Google Patents

Abstract

A fire alarm system for a building comprises a system of pressurised tubes 25 connected to temperature sensors 26, 27 in the various rooms, the sensors being arranged to vent the tube at a predetermined temperature, the drop in pressure in the system then serving to give an alarm, to signal the fire-brigade, to shut down the air conditioning and to bring all lifts to the ground floor. The tubes are pressurised with compressed air and they are made of Nylon so that any damage, e.g. by heat also acts to vent the pressure. The tube system may be connected to a water supply so that any sensor responding to excessive temperature acts also as a sprinkler. <IMAGE>

Description

SPECIFICATION Pneumatic fire alarm system OBJECT: The Pneumatic Fire Alarm System is a fire detection system for the purpose of detecting a fire in a building in its early stages. When a fire is detected, a local alarm is raised for the evacuation of the building, a signal is sent direct to the local fire bridge watchroom, air conditioning operations are shut down and lifts are called down to the ground floor. On receiving the signal the fire brigade immediately despatches assistance to the scene of the fire.

The system can be adapted to any type of building. The equipment used is not of a sophisticated nature and once installed can be maintained by a layman. However, periodic testing by qualified personnel is recommended.

With the exception of the power point required to operate the fault bell and the compressor, mains electric power is not required and the system is completely safe.

Once made air tight and with the fault bell installed, false alarms will be minimal. Electric storms, draughts and unusual temperature changes which are responsible for many false alarms will have no effect on the Pneumatic System.

The system is "fail-safe" as any damage caused to the Flexible Nylon Plastic Tubing or to the Sensors will cause the air to exhaust from the system and activate all the alarms.

Obstructions in the tubing can be easily detected as the tubing is continuous throughout.

Thus, by forcing air in at one end, a steady stream of air out of the other end will indicate the air line is clear.

The system is designed as a "low cost detection system" as an inducement to the owners of small buildings, such as shops, offices, schools, home units and dwellings to install an effective alarm system. To date the cost of Electric Fire Alarms is prohibitive to this type of building as the equipment is so sophisticated and expensive.

OPERATION: The Fire Detection Sensors are installed throughout the building so that there is a maximum of 9m2 of floor area or (21m2 of floor area) to each sensor depending on the Hazard Classification of the building. The sensors are joined together by a continuous length of Flexible Nylon Plastic Tube 8 mm O.D. (from now on referred to as tubing) commencing at a control panel and when all the sensors are joined, returning again to the control panel. By means of a compressor air is then pumped into the tube to a pressure of 700 kPa, and by closing a stop valve situated at each end of the tube the pressurised air becomes static.

Pressure Switches are connected to the tube at the control panel governing a local alarm fire bell and a direct fire brigade alarm.

Other pressure switches are installed to perform such duties as the calling down of lifts and the shutting down of air conditioning installations, in the event of a fire. All these pressure switches are set to operate should the air pressure in the tubing fall more than 1 30 kPa. An additional pressure switch is installed to operate a warning bell when the pressure drops more than 40 kPa, to generally indicate that there is slow leakage of air from the system which requires investigation.

A sensor is activated when the ambient temperature rises to 57"C. The air bubble in the sensor is absorbed by the liquid, which expands and bursts the glass bulb. A closed valve then falls away, permitting the pressurised air in the tubing to exhaust. The pressure switch contacts are automatically closed as the air pressure falls below 570 kPa and the alarms are raised.

PNEUMATIC CONTROL PANEL COMPONENTS (1) For the pressurizing of the tubing a small compressor of a capacity of 2.5 c.f.m. to a maximum pressure of 1050 kPa, with a Single Phase 1 H.P. Electric Motor is used. The compressor need not be a permanent component as a Steel Cylinder pressurised to 14,000 kPa and having a Dual State Regulating Valve can be used to jack up the installation pressure. This operations is carried out manually.

(2) A Ball Valve which is closed when the required installation pressure is attained, i,e, 700 kPa and isolates the source of air.

(3) A separator which extracts oil or water discharged by the compressor into the installation tube.

(4) A back pressure valve.

(5) A Pressure Switch (Mercury Switch+Range O to 1050 kPa-1 2 volt D.C. operated dual contacts-for Local Fire Bell Alarm and Direct Fire Brigade Alarm.

(6) A 1 2 volt dry cell battery being the power supply to the local alarm bell.

(7) A Pressure Switch (Micro-Switch) Range O to 1050 kPa 240 volt A.C. operated single contacts-for Pressure Loss Fault Alarm Bell.

(8) A Pressure Gauge-Range 0-10 Bars to indicate Static Air Pressure of Installation.

(9) A Ball Valve which is always open, except when the valves are required to be isolated from the rest of the installation or maintenance purposes.

(10) A150 mm diameter Fire Bell (11) A 100 mm. diameter Pressure Loss Fault Alarm Bell (12) A Contacts Box for connection of direct private line to Fire Brigade.

(13) Eye Ball Visual Indicators and Test Valvesone to be provided for each floor level or zone of the building where sensors have been installed.

(14) A 240 volt general purpose outlet for Pressure Fault Bell and Compressor.

SENSORS: The sensor is an approved Fire Sprinkler Head generally used in Fire Sprinkler Systems. It is the glass bulb type rated at 57 Colour Orange but does not have a water distributor. It can be installed pendant or upright with metal escutcheon plates when situated below ceilings with concealed tubing.

RESULT OF DAMAGE TO TUBING AND SENSORS: The reaction will be the same as a sensor operating. The air will exhaust from the tubing, followed by a fall in pressure which will activate the alarm switches.

TUBE AND FITTINGS The flexible Nylon Plastic Tube has a continuous resistance to heat up to 79 C-a resistance to distortion up to 126 C at 450 kPa-is self extinguishing-is resistant to attack by weak acids, alkalies and common solvents. A slight discoloration is the only change in the tube caused by sunlight. The recommended size of the tube is the standard 8 mm. O.D. (5/16") At the control panel the fittings in the form of tees, elbows and reducers for connection to the components are brass screwed connections with compression rings and sealing tape.

For the installation of the tubing and sensors the push-in type of fitting is recommended to connect the droppers to the main tube with brass reducers at the end of the droppers to the sensor.

DETECTION OF OBSTRUCTIONS AND TESTING The tubing is installed in one continuous length commencing at the control valves and terminating at the Eye Ball Visual Indicator and test valve. By connecting and operating a compressor pumping air into the system and building up a pressure to approximately 700 kPa then opening a test valve, a sudden gush followed by a steady flow of air from the valve will indicate that the air line is clear. It will also test the efficiency of the Eye Ball Indicator and Alarms.

EYE BALL VISUAL INDICATOR: It is a plastic housing containing a small plastic ball which revolves when air pressure is applied. The ball is coloured one half black and one half red. The indicator is connected by tubing to the system which when pressurised exposes the portion of the ball which is coloured black. When the air exhausts the ball revolves exposing the portion coloured red.

The diagrammatical sketch describes a Pneumatic Fire Alarm System and the components are identified by reading the sketch in conjunction with the following legend: LEGEND (1) Steel Cylinder charged with compressed air to 14,000 kPa (2) Dual-State Regulator Valve (manually operated) (3) Ball Valve--normally closed (4) Connection for Compressor (5) Separator (6) Tee fitting-plugged off (7) Non-Return Valve (8) Pressure Gauge (9) Pressure Switch-Dual Contacts-Local 8 Direct Fire Brigade Alarm (10) Pressure Switch-Pressure Loss Fault Alarm (11) Isolation Switch (12) 1 2 Volt Dry Cell Battery-for Local Alarm (13) General Purpose Outlet 240 Volt-For Compresso 8 Pressure Loss Fault Alarm (14) Local Fire Alarm Gong (1 5) Pressure Loss Fault Alarm Bell (16) Contact Box-For Telecom Direct Fire Brigade Private Line Connection (17) Ball Valve-To isolate Control Panel from installation (18) Flexible Nylon Plastic Drain mm O.D.

(19) Flexible Nylon Plastic Tubing-25mm diameter.

(20) Brass Fittings (21) Flexible Nylon Plastic Test Line (22) Eye Ball Visual Indicator (23) Test Valve (24) Non-Return Valves-to prevent exhaustion of the whole system when a sensor operates on any one level or zone.

(25) Flexible Nylon Plastic Air-Line-8 mm. O.D.

(26) Flexible Nylon Plastic Droppers to Sensors (27) Sensors (28) Steel Control Panel Cabinet (29) Operation Instructions (30) Isolation Valves.

PNEUMATIC FIRE ALARM AND SUPPRESSION SYSTEM.

(to be used in conjunction with a Standard Fire Hydrant and/or Hose Reel Installation) The above is a development of the previously described Pneumatic Fire Alarm System. The principal of detection and the raising of the alarms is the same with the addition that water is permitted to enter the tubing and discharge in the vicinity of the fire when a sensor operates.

In order to do this efficiently the size of the tubing is increased to 25 mm. l.D. and a set of Hydraulic Control Valves added at the Control Panel.

The water supply is drawn from the same water main which feeds the Fire Hydrants and/or Hose Reels which are installed in most buildings in accordance with the Building Act 1 975. The system becomes, and is intended to be, an integral part of the Hydrant/Hose Reel installation but does not detract from the normal efficiency of the installation in any way.

The water supply can be introduced: (a) Manually at all times when the possibility of water damage is critical (b) Manually operated when the building is occupied and automatically when the building is unoccupied (c) Automatically at all times.

thus provision is made in varying conditions which may include the consideration of water damage.

The system again is designed as a "low cost detection and suppression system" for use in the smaller type of building. It is satisfactory for buildings up to 1 5 metres in height having floor areas of up to 1,000 square metres per storey, but is restricted to occupancies of the Extra Light Hazard Classification-See S.A.A. Code for Automatic Fire Sprinklers SA 2118-1978. It is not mandatory for buildings of the above-mentioned dimension to install automatic alarm and suppression systems and consequently because such systems are very costly due to the sophisticated equipment used, very few of these buildings are protected by other than a Hydrant/Hose Reel Installation.

Calculations of flow/pressure requirements of the water supplies required by the Hydrant/ Hose Reel Installations are suitable for this Pneumatic System also when using the 25 mm.

tubing and restricting the size of the buildings as previously described. In all but the extreme cases, the design density of discharge as required for Fire Sprinkler Systems in the Extra Light Hazard Occupancies can be achieved.

OPERATION: The fire detection sensors are installed as previously described throughout the building. They are joined by a continuous length of 25 mm. P.V.C. or a combination of Galvanised Steel and P.V.C. tubing commencing at and returning to the control panel. Air is then pumped into the system to a pressure of approximately 1 .000 kPa and by closing the stop valves at each end of the tubing the pressure becomes static.

To the air line is connected a 40 mm. Galvanised Steel Water supply line, the water being controlled by a single Stop Valve for a Manually operated system or by two stop valves and a "Pinch" (or diaphragm valve) when automation is preferred. By connecting a Flexible Nylon Plastic Tube from the compressor side of the check valve in the Pneumatic Control Panel to the "Pinch" Valve the diaphragm is closed when the system is pressurised. This holds back the water supply until such time at the pressure in the system falls below the water pressure which is assumed to be in the region of 700 kPa for the purpose of this exercise.

Pressure Switch settings would be in this instance: (a) Pressure Loss Fault Bell960 kPa (b) Local Alarm 8 Direct Fire Brigade Alarm870 kPa (c) Air Conditioning and Lift Shut Down-870 kPa Thus there would be a short time delay from when the alarm is raised until the water enters the system.

CONTROL PANEL COMPONENTS Pneumatic control panel components As for the Pneumatic Fire Alarm System, with the addition of a Flexible Nylon Plastic Tube connection to the "Pinch" Valve.

Hydraulic Control Valves

(a) One only 40 mm. Stop Valve for Manually Operated Water Supplies (b) Two only 40 mm. Stop Valves ] for automatically One only 25 mm. Test 8 Drain Valve } operated One only 40 mm. Pinch or Diaphragm Valve J water supplies (c) One 0-1000 kPa Pressure Gauge SENSORS: The sensor is an Approved Fire Sprinkler Head generally used in Fire Sprinkler Systems.It is the glass bulb type rated at 57 Colour Orange and has the spray type distributor. There are two types-the pendant and the upright, both of which may be used bu the upright type is preferred whenever possible.

TUBE AND FITTINGS The Flexible P.V.C. tubing has a continuous resistance to heat up to 65 C-is slow to self extinguishing-is resistant to alcohols, aliphatic hydrocarbons and oils. An alternative to the use of Flexible P.V.C. tubing (Flexible Nylon Plastic Tubing is not readily available in 25 mm.

dimensions) is 25 mm. Galvanised Medium Steel Piping. Preferably, where rising mains are concealed in brick or concrete ducts they should be of P.V.C., the pipes feeding the sensors 25 mm. Galvanised Steel, the bends on the Galvanised Pipework 32 mm. P.V.C. slipped over Galvanised Steel Pipes, sealed with a suitable compound and clamped with worm drive steel clamps. The use of P.V.C. bends will reduce friction losses considerably and speed the erection process.

Droppers from the Galvanised Steel Pipework should be of 1 5 mm. O.D. Flexible Nylon Plastic Tube with brass connections to the sensors. This will permit the sensors to be located in the centre of ceiling tiles or in the desired position without the use of swivels which could not be permitted in Pneumatic Systems.

Outlets from the Galvanised steel pipes will be welded in sockets. At the control panel the Flexible Nylon Plastic Tubing 8 mm. O.D. with brass fittings will be used as for the pneumatic fire alarm system.

The water supply line from the Hydrant/Hose Reel main is of 40 mm. Galvanised Medium Steel Pipe, screwed or flanged to the control valves. Connections to the plastic pipes are by means of brass bushes and connections.

WATER SUPPLY TO SENSORS As described in the diagrammatical sketch the water, when introduced into the installation pipework will enter from each end of the system and by means of the "feeder pipes" ie. pipes with non-return valves which short circuit the pipework, will find the shortest route to the activated sensor. Non-Return Valves close to the rising mains will prevent the whole system exhausting when a sensor operates on any one level or zone and also prevents water entering parts of the system when not required.

TESTING AND DRAINING ti From each zone or level a Flexible Nylon Plastic Tube 8 mm. O.D. is taken from the extremity of the main tubing and returned to the control panel where an Eye Ball Visual Indicator and Test Valve is situated. This will enable the pneumatic action of the system to be tested. A test valve shown at the Hydraulic Central Valves will enable the "Pinch" valve to be tested. A by-pass and stop valve on each level, when the valve is opened will enable the water to be drained from the system following a fire.

The "Pinch" Valve test valve will also be opened during this operation.

TESTING PROCEDURE (To be read in conjunction with Dwg. No. 3) Manual In a manual system stop valve "B" is "normally closed." This valve controls the water supply from the Hydrant Main and is only opened when a fire is in evidence.

When fully installed, the pressure switch to raise the alarms is set to 870 kPa and the pressure switch to the fault bell to 960 kPa. The system is then charged with air to 1 ,000 kPa and with valves B, C, D and all test (F) valves closed the installation will remain in this state.

The only valves left open are the pressure switch and gauge isolation valves and valve E.

Should slow leakage occur, the pressure switch set to operate at 960 kPa will activate the fault bell when the pressure in the system falls to this level. Valves C and D should then be opened and the pressure again raised to 1,000 kPa. The valves are then closed again.

Should a detector operate through fire or by accident, the pressure in the system will fall rapidly and when it is reduced to 630 kPa, the pressure switch set at this reading will activate the local and Fire Brigade Alarms. Water will not, however, enter the system until the Stop Valve "B" is turned on manually.

When the danger is passed, the system is reactivated by: (a) Turning off Valve "B" (b) Blowing unwanted water out of the system by the use of a compressor (c) Replacing the detectors which have operated (d) Recharging the lines to a pressure of 1,000 kPa (e) Re-setting the pressure switches and alarms In an Automatic System Valve "B" can be closed when the building is occupied. This is to avoid water damage should a detector operate accidentally. When the building is unoccupied Valve "B" is left open. Should a detector operate in an unoccupied building. it is almost certain it is an indication that a fire is in evidence.

Note: It is recommended that a security patrol be engaged to check that valve "B" is open when the building is unoccupied.

When fully installed the system is treated as described in paragraph 3, but in addition, Valve "A" is left "normally open.

Should an automatic system operate when the building is unoccupied, the alarms will be raised as described in paragraph, but when the air pressure falls below the pressure in the water mains, the water will flow into the system and discharge through the detector which has operated.

Reactivating the system is carried out in exactly the same way as described in paragraph 53.

TESTING To test if all lines are clear of obstructions: (a) Turn off Pressure Switch Isolation Valves and open Valve "C" (b) Connect and turn on compressor (c) Open test valves in indicator panel alternately and observe if air flows through freely through each line.

Check also if Pneumatic Visual Indicators are operating.

In the case of an automatic system Valve "A" should be closed during the above procedure.

To test alarms, Pressure Switch Isolation Valves are left open and only one valve in the indicator panel need to be opened to reduce the pressure in the system to 870 kPa when the alarms will operate. The Fire Brigade must always be advised before hand that tests are being carried out.

To test Mini-Flex Pinch Valve in an automatic system: (a) Close Valve "A" (b) Open Valve "B" and two adjacent test valves '9'.

(c) When water flows freely to the drain, turn off valve "B" and the test valves.

(d) Open up valves C 8 D and when air pressure in the line equalises at 1 ,000 kPa, close them again.

(e) Re-open "A".

After testing be sure: (a) Pressure Switch Isolation Valves are locked open (b) Valve E (and A if automatic) is strapped open (c) Valve B and all test valves are closed.

(d) The air pressure in the system is steady at 1,000 kPa (e) The fault bell switch is on.

Testing and reactivating should always be carried out by trained staff, preferably employed by the Company responsible for the installation of the equipment.

FLOW/PRESSURE RESULTS AT MOST UNFAVOURABLY POSITIONED SENSOR WHEN THE CALCULATIONS ARE BASED ON THE MINIMUM WATER SUPPLIES REQUIRED BYA FIRE HYDRANT INSTALLATION Assume a five level buiding, a height of 1 5 metres, and having 50 Sensors on each level:- a total of 250.

A Hydrant Main supplies Fire Hydrants and Hose Reels on each level. In accordance with the Building Act of 1 975 a running pressure of 400 kPa and a flow rate of 750 litres per minute must be available at the Hydrants on the uppermost level.

The running pressure at the ground level will be: Required pressure at 1 5 metres = 400 kPa Loss of pressure due to static = 1 48 kPa Loss due to friction in pipes = 14 kPa Minimum Pressure required = 562 kPa The design density of discharge in accordance with the Fire Sprinkler Code for E.L.H. is 2.25 mm/min. over an assumed area of operation of 84 m2. On calculation this assumes the simultaneous operation of 4 sprinklers. As the Pneumatic Systems are supplied by water from two 25 mm. pipes, each feeding from opposite ends of the system, the pressure/flow requirements can be assessed on the basis of two sensors to each pipe.

Then from the running pressure of the Hydrant Main, being 562 kPa the running pressure available at the top of the 25 mm. riser equals: Hydrant Main Pressure 562 kPa Loss of Pressure due to static 148 kPa Loss of Pressure due to friction in 25 mm. pipe 69 kPa Pressure at the top of 25 mm. riser = 562 - 217 = 345kPa The most unfavourably positioned sensor on the system to conform to the E.L.H. requirements is required to discharge 51 litres per minute at a running pressure of 79 kPa through a 10 mm.

orifice and at the second most unfavourably positioned sensor 85 kPa.

From the above information the distance from second most hydraulically unfavourably positioned sensor to the top of the 25 mm. Riser can be calculated (Bends not taken into account), Pressure at top of 25 mm. Riser 345 kPa Pressure at 2nd most unfavourable sensor: 85 kPa Pressure difference 260 kPa Friction loss in 25 mm. pipework at a flow rate of 102 litres per minute = 4.52kPa per metre.

Then length of Pipework = 260 = 57.4 metres 4.53 CHECK Total friction loss in 25 mm. pipe at flow rate of 102 I/min = (57.4 + 15) = 72.4 X 4.52 = 327.2 kPa Loss in pressure due to static head = 15 metres X 9.7= 145.5 kPa Total loss = 472.7 kPa per metre Then running pressure at second most hydraulically unfavourably positioned sensor = Available pressure in hydrant main 562 kPa Pressure losses in 25 mm. pipes say 473 kPa 89 kPa Running pressure at most unfavourably positioned sensor = Pressure at second sensor 89 kPa Friction loss in 4.6 metres of 25 mm. pipe at flow rate of 51 I/min 6 kPa 83 kPa From the above calculations which are based on an extreme condition, it can be assumed the system will safely cater for the type of buildings for which it has been designed.

LEGEND.

The diagrammatical drawing describes the Pneumatic Fire Alarm and Suppression System.

The components are similar to the components for the Pneumatic Fire Alarm System with the addition of the following..

(31) Drain lines and valve 25 mm dia.

(32) Feeder pipes with non-return valves-25mmdia.

(33) Hydraulic Stop Valves---40mm dia.

(34) "Pinch" or diaphragm valve 40mum dia.

(35) Fire Hydrant/Hose Reel water supply.

(36) Drain Valve.

(37) Test Valve to test "Pinch" valve.

(38) Flexible Nylon Plastic 8mm dia. air line to Pinch Valve (39) Galvanised steel pipe 40mm dia water supply branch line The system again is designed as a "low cost detection and suppression system" for use in the smaller type of building.

It is satisfactory for buildings up to 1 5 metres in height having floor areas of up to 1 ,000 square metres per storey, but is restricted to occupancies of the Extra Light Hazard Classification-See S.A.A. Code for Automatic Fire Sprinklers SA 2118-1978. It is not mandatory for buildings of the above-mentioned dimension to install automatic alarm and suppression systems and consequently because such systems are very costly due to the sophisticated equipment used, very few of these buildings are protected by other than a Hydrant/Hose Reel Installation.

Calculations of flow/pressure requirements of the water supplies required by the Hydrant/ Hose Reel Installations are suitable for this Pneumatic System also when using the 25 mm.

tubing and restricting the size of the buildings as previously described. In all but the extreme cases, the design density of discharge as required for Fire Sprinkler Systems in the Extra Light Hazard Occupancies can be achieved.

Claims (4)

1. The Pneumatic Fire Alarm System is a combination of components and pipework arranged in such a way that should a fire occur in the building in which it is installed, the following results will be achieved: (1) A Local Evacuation Alarm Bell will ring and the Eye Ball Visual indicator will register red (2) A signal will be despatched to the Local Fire Brigade Watchroom and call the Brigade to the scene.

(3) Air Conditioning Plants will be shut down (4) Lifts will be brought down to the ground floor.

The claim for protection of the system is based on the assumption that it is the first alarm system which has been proved successful when operated pneumatically.

2. The simplicity and economics of the design will provide Fire Alarm protection to buildings which do not normally install protection other than Fire Hydrants/Hose Reels. Thus a claim for the protection of the design is proffered.

3. The desirability of a system which includes methods for the control of water damage as well as fire and at the same time keeps the installation costs within economic bounds is a featue contained in the Pneumatic Fire Alarm and Suppression System and on these grounds a claim is made for protection for the design and construction of the system.

4. The Pneumatic Fire Alarm and Suppression System is installed as an integral part of a Hydrant/Hose Reel Installation and as such a claim is made that it is an improvement on the existing Hydrant/Hose Reel systems.