A SURVEY OF MODERN FIREFIGHTING PRACTICE AND EQUIPMENT

By G.CAIN, M.I.FireE. (Visitor)

ABSTRACT

The techniques of modern fire fighting and fire prevention with a description of the latest types of major fire appliances commonly used by the peacetime fire service. A survey of the various types of equipment available for fire fighting. Automatic fire alarms, and two-way radio transceivers, their operation, and value. Recommendation for a national fire fighting service.

CONTENTS

1.      Introduction

2.      Subject

3.      Fire prevention

4.      Water and pumps

4.1.  The use of water

4.2.  High-pressure spray (Fog)

4.3.  Low-pressure spray

4.4.  Jets

5.      Chemical and gas extinguishers

5.1.  Dry powder

5.2.  Foam

5.3.  Inert gas

5.4.  Viscos water

6.      Fire fighting vehicles

6.1.  Petrol or diesel power

6.2.  The pumping unit

6.3.  The turntable ladder

6.4.  The hydraulically operated elevating platform

6.5.  The foam tender

6.6.  The emergency recovery and breakdown unit

6.7.  The emergency tender

7.      Communication

7.1.  The telephone

7.2.  Two-way radio

7.3.  Automatic fire alarms

8.      Conclusion

1.      INTRODUCTION

Advances in the techniques of fire fighting and the production of new equipment over the past twenty years could have been more spectacular when the comparison is made with the great scientific and industrial development which occurred over the same period. As an analogy, take the advancement in the design of the internal combustion engine; it develops more power and has a number of extra gadgets, but its basic principle of operation is the same as it was when first discovered.

2.      SUBJECT

In this paper, it is proposed to outline the trend in modern fire fighting and fire prevention practice and to describe the latest equipment which is available to the service.

3.      FIRE PREVENTION

In the early days of fire fighting, the main emphasis was on fighting and extinguishing such fires. as occurred. The modern conception is to prevent, eliminate or reduce hazards that contribute to the occurrence and to the spreading of the fire thereby reducing the damage which inevitably results from fire and from its extinction.

In most large brigades, fire prevention is considered important enough to justify the appointment of full-time fire prevention officers specially trained to identify fire hazards and to make recommendations for their removal. Control is exercised over all premises where flammable liquids and substances are stored or used. The protection against fire of buildings is discussed with architects and designers who are thus made aware of the requirements of the prevention branch in the planning stage.

In addition, the scope of the fire prevention branch includes facilities for training the personnel of factories, warehouses, hospitals and schools by means of lectures and films in the practical application of fire appliances. A photographic section is available to assist in the investigation after a fire has occurred. Models of spray painting booths, flammable liquid stores, and petrol pump installations are available to architects and builders. These depict desirable methods of construction together with the correct siting of fire fighting equipment.

4.      WATER AND PUMPS

4.1.  The use of water

The song, London's burning pour on the water probably derived its origin from the great fire of London III the year 1666 where leather buckets were used to pour on the water. At the early part of this century, steam was harnessed to supply energy to the water used at fires whereas the internal combustion engine is the modern method. Compare the old and the new machines shown in Figs. 1 and 2.

With few exceptions, water has been and probably always will be the fire fighter's best medium for extinguishing fires. The latent cooling properties of water can be appreciated when one considers that one gallon will absorb about 1 500 B.Th.U's in the process of raising its temperature from 62 to boiling point and a further 10 000 B.Th.U's in the process of converting it to steam. Steam in itself is a useful fire extinguishing medium. The maximum cooling effect of water on fire cannot be obtained by Its application in a jet form, because about 90 percent of i.t runs to waste. It has been found necessary to design a nozzle which will convert the stream from a hose into a fine spray so that a greater proportion of the water will be converted to steam. This type of nozzle, which is used in the fire service, is available in a range of sizes which vary in capacity from 4 g.p.m to 1 000 g.p.m. Figs. 3, 4 depict the various nozzles.

4.2.  High-pressure spray (Fog)

The 'first aid' pump and equipment consisting of a double helical gear pump which delivered water through a hose reel and a 3/16 inch diameter jet nozzle at 80 p.s.i. that used to be fitted to all fir pump vehicles has been superseded by the high pressure say or fog pump. Fed from 400-gallon water to the vehicle, this pump delivers 50 g.p.m. at 500 p.s.i. through a ? inch or 1-inch diameter rubber hosepipe to the 'fog gun,' which is trigger operated and has adjustments for either jet or spray application.  The hosepipe is tested to withstand 1 000 p.s.i. pressure. The pump is a single-stage centrifugal unit which has a bronze casing and impeller and a stainless steel driving shaft. The shaft seals are carbon faced. The integral gearbox has a ratio of 3 to 1 and 100 h.p. is required to drive the pump impeller at 6000 r.p.m. This type of equipment has proved extremely useful for extinguishing a fire in its early stage with a minimum amount of water damage.

Some years ago when the high-pressure fog was first introduced, a gleaming n w fire engine arrived at the scene of a fire where a building containing furnishings was involved and the crew g to work smartly inside the building with their fog guns. The water applied must have been in the exact quantity and fineness required for its complete conversion to steam because the firemen baled out so smartly to escape being scalded. As it has been found virtually impossible to determine by snap judgment the amount of heat generated in any fire, firefighters are inclined to apply more water than is necessary.

4.3 Low-pressure spray

The standard 2t inch diameter rubber-lined hose is tested to 350 p.s.i. and normally works at pressures between 80 and 130 p.s.i. The delivery of large quantities of water in the form of a spray is therefore limited to the pressures that the hose can withstand. Spray nozzles that are available for use with a fire hose, range in delivery capacity from 100 to 1.000 .g.p.m. Because of the reaction force when water is delivered from a nozzle, the larger capacity nozzle has to be operated from a fixed position, such as a turntable ladder, an elevating platform or a ground monitor.

The jet reaction is calculated on the formula 2 p.a. where p is pressure and a is an area of the nozzle in square inches. On the basis of this formula the reaction at 100 p.s.i. with a flow of 100 g.p.m. would be 85 lb and with a flow of 1 000 g.p.m. at the same pressure it would be 630 lb.

When water is applied to flammable liquids in the form of a Jet, it scatters the fuel and increases the burning surface. It is highly effective in diffused form, however. The principle of using diffused water has been adapted for the protection of outdoor electrical equipment such as oil-cooled transformers and switchgear. Fixed automatic installations operate in the event of a fire. From tests carried out by the Paris Fire Regiment, the minimum distance for the safety of the operator when applying diffused fresh water on a conductor with a d.c. the voltage of 150 000V was found to be 6 feet. The minimum safe distance when using a jet of 5/8 inch diameter on a conductor at 30 000 volts is 15 feet.

4.4 Jets

By diffusing the water, the effective reach or throw is considerably reduced thereby limiting its use to fires which can be approached to within easy striking distance, In the case of conflagrations or fires beyond the reach and capacity of spray nozzles, the jet nozzles as used in the early part of the century are still a feature of the modern fire service. The 'Streamform' branch pipe shown in Fig. 6, which was designed during the 1914-18 war, is possibly the finest example of this type of equipment in use today. It is fitted with an inner tube one inch in diameter which accounts for the excellent jet of water produced. The nozzles are interchangeable and range from t inch diameter to It inch diameter, delivering respectively 60 g.p.m. and 550 g.p.m. at 100 p.s.i.

5.      CHEMICAL AND GAS EXTINGUISHERS

Good progress has been made in the field of chemical fire extinguishing mediums which include dry powder, all-purpose foam compounds, inert gas, and synthetic wetting agents.

5.1 Dry powder

The main ingredient of dry powder extinguishers consists of finely ground sodium bicarbonate or potassium bicarbonate with a small number of other chemicals that prevent the caking of the powder. Supplied in cylinders at a pressure of 225 p.s.i. in capacities from 2t lb to 150 lb, the powder is discharged by the pressure of 'either carbon dioxide or nitrogen in the cylinder. The powder is efficient when used on burning gases from petrol, benzol, naphtha and on fires in oil quenching tanks and oil-fired furnaces.

5.2 Foam

The demands of modern industry have resulted in the establishment of numerous depots for the bulk storage of flammable liquids. The majority of these depots are protected by foam installations. Foam compounds are produced either in powder form or as a liquid, the latter being known as air foam because the final mixture of water and compound must be aerated. The compounds are made from hoof and horn meal stabilized with ferrous sulphate or based on the caustic soda hydrolysis of animal blood with the same stabilizer. When the compound is mixed with water in a pipe or hose line, it expands and forms a light heat-resisting and air-excluding blank over the surface of the burning fuel. The ratio of compound to water is 5 parts to 100 parts and produces 1 000 parts of foam. Because such water-soluble flammable liquids as methyl alcohol, ethyl alcohol, isopropyl alcohol, diacetone alcohol and acetone break down the stability of the abovementioned foam, a synthetic all-purpose compound, the ingredients of which are not published, has been made available for use on fires involving these liquids. It is applied m a similar manner but after application, the foam hardens to form a tough stable blanket.

5.3 Inert gas

Recent research with inert gas for the extinguishing of fires in ship's holds, basements and tunnels have resulted in the production of an inert gas generator. The generator consists of a turbo-jet engine with an afterburning section and with facilities for spraying water into the exhaust gas stream. The exhaust gases have a temperature of about 400°C and contain 18 percent by volume of oxygen. The oxygen content is reduced to 12 percent by burning additional fuel in the afterburning section. The gases are tl1en cooled by the water spray, reducing the oxygen content further. The analysis of the gas produced is nitrogen 46 percent, carbon dioxide 3 percent, water vapour 44 percent and oxygen 7 percent. The gas is slightly lighter than air and has a sufficiently low oxygen content to extinguish the flame.

5.4 Viscous water

To extend the effective cooling properties of water further, experiments with chemical additives have been conducted in America recently with encouraging results, especially where the solutions are used on forest fires and on materials that have a tendency to smoulder. The chemical used is the sodium salt of carboxymethyl cellulose which when mixed with water increases its viscosity thereby creating a flow behaviour similar to that of dripless latex paint. Because of this feature, the mixture tends to stick to the burning fuel and so increases the cooling property of the water and at the same time delays the heating of unburned material covered with the foam. Further, a jet of the solution does not drift or feather to the same extent that plain water does. A greater 'throw' is thus possible. A mixture of four-pound of the chemical to 100 gallons of water yields a viscosity of approximately 200 centipoise which results in a solution several times as effective as plain water. As the solution is corrosive, fiberglass or coated tanks are required for the storage of the mixture.

6. FIRE FIGHTING VEHICLES

6.1 Petrol or diesel power

It has always been accepted that a fire service vehicle should have an effective operational life of about twenty years because of the low mileage it covers over the years. This is indeed so but the cost of repairs and maintenance over the last few years of its life is staggering. Up to ten years ago the petrol engine was used exclusively in fire vehicles. Then the compression ignition engine, which had to improve in design, was introduced to the fire service. The fire appliance power unit is subject to unusual conditions of operation. Its life is composed of number us quick starts, short runs and long periods of idleness. Under these conditions, the high-speed petrol engine is subject to rapid cylinder wear owing to the use of the choke, in starting. Lubricant is washed off the cylinder walls and the oil in the sump is diluted. The short runs do not allow the engine to heat up sufficiently to drive off the petrol in the oil. The compression ignition engine, on the other hand, develops its maximum power at approximately half the revolutions of the petrol engine and no cylinder wall washing or oil dilution takes place when starting. It seems that the compression-ignition engine will prove to be better suited to fire service conditions than the petrol engine.

6.2 The pumping unit

Generally, fire service pumping units fall into three categories, namely light, medium and heavy, the delivery capacities being respectively 250, 500 and 1000 g.p.m. All modern vehicles are equipped with either separate high pressure and low-pressure pumps or a single pump delivering both high and low pressures. The centrifugal-type of the pump with one or at the most two stages is the one commonly used. The priming mechanism may be either of the positive displacement, the water ring or the engine vacuum type. The performance data of the combined high/low-pressure medium pumping unit is as follows:

The pump is, of course, only part of the fire fighting appliance. The appliance is provided with various nozzles and branch pipes, delivery hose, suction hose, 35 ft and 15 ft aluminium ladders, terylene lifelines, breaking-in tools, breathing sets, adaptors, spanners, and torches. The main pump is mounted either at the front, amidships or at the rear and power is supplied to it from the engine of the vehicle. Seating accommodation is provided for a crew of six men.

6.3 The turntable ladder

The turntable ladder is essential for fire fighting and rescue operations in cities where high buildings predominate. A 500 g.p.m. monitor is fitted at the head of the ladder for attacking fires in upper floors of buildings and rescue equipment consists of a bosun's chair with pulleys and 220 ft of t inch diameter nylon rope. An inter-communication system is provided between the head and base of the ladder. The standard 100 ft unit is constructed in steel and has a main section and three extensions operated by steel wire ropes. The ladder mechanism is driven by the vehicle's engine. The only operating panel is at the base of the ladder. On it there are three levers that control all movements of the ladder, i.e. rotation in either direction, elevation or depression, and extension or lowering. The levers actuate valves to control the flow of oil under a pressure of 80 p.s.i. to cylinders which engage one of the ten clutches that provide power to the train of gears corresponding to the desired movement. The mechanism embodies an automatic plumbing device. Overload cut-outs are provided in the oil pressure system. Automatic stabilizing jacks give rigid support to the chassis when the ladder is in operation. In addition, the vehicle is fitted with a 500 g.p.m. fire pump driven by a separate motor. Fig. 7 illustrates the control panel on the ladder.

6.4 The hydraulically operated elevator platform

The first hydraulically-operated platform was constructed in the U.S.A. It had a working height of 18 ft and was used mainly for picking fruit from high trees. Its versatility was foreseen and industrial models with a working height of up to 50 ft made their appearance. In recent years, it was developed for use in the fire service and units with 50 ft and 65 ft reach have been commissioned. Except that it cannot reach so high it provides a greater range of operations than the turntable ladder. With its large weight lifting capacity, a greater volume of water can be delivered. The cage or platform at the end of the boom can accommodate five men. A typical 65 ft unit is mounted on a 7t-ton chassis powered by a 105 b.h.p. diesel engine. It has a turntable on which is mounted the boom consisting of two hinged sections 25 it and 35 it long. There are four outrigger jacks for leveling and stabilizing the vehicle. The turntable rotates through 3 600 and is driven by hydraulic motors with worm reduction gearboxes. The lower boom has a movement of 820 above the horizontal. With the lower boom in the highest position, the upper boom can move through 1 500. Each boom is actuated by a 6 in bore hydraulic cylinder having a 4 ft 6 in stroke. The floor of the cage remains level in any position and has 14 sq. ft of floor space. The maximum permissible load in the cage in any position of the boom is 1 000 lb. The platform may be operated either from the ground or from a duplicate set of controls in the cage. An inter-communication system is provided between the cage and its base. The cage is fitted with a variety of nozzles (jet and spray) which may be controlled to deliver from 100 g.p.m. to 1 000 g.p.m. from the monitor. The monitor is permanently connected to a 31 in water supply pipe which extends from a collecting head at the rear of the vehicle along the length of the booms. The cage has an operating range of 13 ft overhang at 60 ft height to 34 ft overhang at 3 ?  ft height. Fig. 8 shows the range of the unit. Fig. 9 shows the cage and its equipment.

6.5 The foam tender

In most modern cities, the danger of extensive fire due to flammable liquids is ever-present. Great quantities are transported through the streets daily. An accident involving any of the many vehicles carrying up to 4 000 gallons could spark off an inferno. Only recently, an aeroplane crashed into a large town. Its burning fuel was scattered over a wide area resulting in a major fire operation. The foam tender has been designed specially to cope with fires where flammable liquids are involved. Fortunately, this type of fire does not occur often and consequently, the vehicle is constructed with high-pressure equipment so that it may be used also as a normal fire pump. The vehicle is fitted with the following pumps: 500 g.p.m. low-pressure pump, 50 g.p.m. high-pressure pump and a 25 g.p.m. foam compound loading pump, all driven from a 195 b.h.p. engine. It carries 400 gallons of water and 350 gallons of foam compound. Four foam branch-pipes which are designed to aerate the compound/water mixture have adjustments for spray or jet application. Foam is produced by inducing foam compound into the intake side of the pump where it is mixed with water passing through the pump and delivered to the four outlets. The pump operates at a pressure of 100 to 130 p.s.i. forcing the mixture through 2t in hose lines to the branch pipes, where final aeration takes place. The pump produces 4 000 gallons of foam per minute from 20 gallons of foam compound and 400 gallons of water.

A recent addition in the field of foam making equipment particularly suited to the protection of oil refineries, storage depots, and chemical works, is the mobile foam monitor. It is capable of producing 5 000 gallons of foam per minute and has an effective reach of 200 feet. Water is supplied through four inlets and the foam compound is drawn into the inductor through a 2 in the flexible pipe which can be inserted into or connected to a suitable supply of foam compound.

6.6 The emergency recovery and breakdown unit

The primary function of the fire service is to deal with fires but it is also equipped to cope with almost any occurrence which constitutes an emergency. In fact, it should be termed an emergency service. The recovery and breakdown vehicle has been designed to provide the tools for this type of service. A typical unit consists of a heavy chassis on which is mounted a powerful winch with 450 ft of ? in diameter steel wire rope with a breaking load of 23 tons. The winch is driven from power take-off on the auxiliary step down gearbox and specially designed pulleys at the rear make it possible 'for the pull to be taken from any angle. It is capable of a direct pull of up to 25 000 lb and by means of snatch blocks, the pull may be increased to 50 000 lb. A heavy-duty towing ambulance is situated transversely on the vehicle for use on vehicles weighing up to 25 000 lb. It is loaded and off-loaded by means of an 8-ton salvage crane fixed on the rear of the chassis. Electric power is supplied from a built-in 7 kW generator which is driven by a two-cylinder 4-stroke air-cooled diesel engine. Four 11 in Benjamin type lights provide illumination for night work. Additional equipment includes two oxy-acetylene cutting plants, one motor-driven chain saw hydraulic jacks from 3 to 20-ton capacity, shear legs, crowbars, picks and shovels, chain and steel rope slings. The vehicle is illustrated in Fig. 10.

6.7 The emergency tender

The emergency tender is another special appliance which has been developed to carry the wide range of equipment now available for use in rescue work. In addition, it is used as a control point for operations involving breathing apparatus at fires. The equipment consists of aluminium extension ladders, a mining type rescue stretcher, portable L.P.G./oxygen cutting sets for clearing obstacles in confined spaces, L.P.G. lamps electric lamps with rechargeable batteries, hydraulic (porto power type) equipment for use as a breaking-in tool, a portable motor-driven smoke extractor used in clearing smoke from basements and having a capacity of 2 000 c.f.m., a portable 110V electric generator for supplying power to floodlights and power tools, oxygen resuscitators for reviving victims of gas or smoke, grappling-irons for underwater work, nylon salvage sheets for protecting goods against damage by water and smoke, a variety of fire hoses and branch pipes and a dozen compressed air or regenerative type of breathing apparatus. Not many years ago, the self-contained breathing set was something rare in the fire service and it was generally accepted that, if a man could not endure a large quantity of smoke, he was not tough enough to be a fireman. One can well imagine the severe punishment the fireman's lungs must have taken under these conditions.

The compressed air breathing set consists of a cylinder mounted on a metal frame supported on the back of the wearer by a harness and belt. A moulded rubber mask secured over the face by a harness incorporates a demand regulator, a speech diaphragm and a perspex visor. The high-pressure air in the cylinder is supplied to the demand regulator and to a pressure gauge by two reinforced flexible rubber hoses. A whistle warning device is fitted which operates when the pressure in the cylinder falls to about 30 atmospheres. The set weighs 29 lb and the cylinder has a capacity of 1 200 liters of air when charged to 132 atmospheres (1 980 p.s.i.). The time the air supply of this type of set lasts depends on the amount of work done by the wearer. The consumption of air and duration of use is as follows:-

A typical compressed air breathing set is illustrated in Fig,. 11.

Unlike the compressed air set where the exhaled breath is expelled to the atmosphere, in the regenerative type the exhaled air is recirculated. It has a replaceable cannister containing, a high oxide of potassium and a catalyst which, upon contact with the moisture in the exhaled breath, evolves a plentiful supply of oxygen and absorbs carbon dioxide and moisture. The set weighs 13t Ib and the cannister lasts for one hour under any conditions. A clockwork warning timer operates a bell when 50 minutes has elapsed. The principle of operation of the set is illustrated in Fig. 12.

Operations using a breathing set especially in dense smoke and humid atmospheres are difficult and hazardous and any known form of lighting is ineffective. Because rigid control over the teams is essential, an accepted form of the procedure has been adopted. The emergency tender is fitted with a two -way radio for communicating with the team who are equipped with one or two portable radios. The speech diaphragm in the face mask makes communication possible. The tender also has a master 'tally board' where the time of entry, the time limit, and the set numbers are logged. Each breathing set has a braille type number corresponding with that on the tally board and a 100 ft x 1/4 in a personal line on a reel. The team operates in pairs. A main t in diameter rope fitted with raised arrows pointing to the exit is fixed at points inside and outside the building. The personal lines are clipped to the mainline so that penetration of 200 ft can be achieved. Apart from the warning devices on the breathing sets, the control officer advises wearers of elapsed time at the interval.

7. COMMUNICATIONS

The success of all operational procedures in the modern fire service depends largely on the maintenance of communications. For a service of this nature, the system of communications must be duplicated in every link so that only a major disaster can put it out of action. Radio telephones, automatic and manual alarm systems and the telephone are all employed to attain this end.

7.1 The telephone

The number of calls to incidents received by the fire department by means of the telephone exceeds by far that of any other system. However, this does not indicate that other systems are not justified. It is because there are more telephones readily to hand. Unlike the practice in some other countries where fire, ambulance or police services can be summoned on a general emergency number such as 999, local conditions preclude this arrangement. As a result, each of these services has a different emergency number which, except for the police, is confined to the local authority's area. In Johannesburg, all emergency calls to the fire department are received at the central station. From here direct telephone lines facilitate the onward transmission of the message to the various sub-stations if necessary. In addition, all theatres have a direct telephone line to the fire station.

7.2 Two-way radio

The rapid development of radio equipment over the past decade has widened the field of communication and today, no fire service operates without it. A complete two-way radio system comprises two base stations, one of which is kept as a stand-by, mobile stations fitted on all vehicles and portable (walkie-talkie) sets. An independent power supply unit at the base station provides power in the event of the town's main supply failing. The base stations have an output of 60 watts which gives a range of about 30 miles, and the mobile stations have an output of 25 to 30 watts. Frequency stability of .0005 percent or better is required to eliminate as much interference as possible.

The portable sets are particularly useful during 'fire ground' operations where messages can be transmitted to any fire vehicle in an instant. The set weighs a little over two pounds and is tuned to the department's frequency. Of the transistor type, it has an R.F. output of 1.4 watts and power is supplied by a nickel-cadmium 14.4-volt rechargeable battery. Based on 10 percent transmit, 10 percent receive with rated audio output and 80 percent standby, the set will operate for 8 hours per charge. On standby, it consumes 4 milliamps, on receive 50 milliamps and on transmits 320 milliamps.

7.3 Automatic fire alarms

The automatic or early· warning fire alarm is not being used to the extent that this invaluable type of mechanism deserves. The probable reason for this being the cost and the fact that establishments are covered by insurance. This is a short-sighted policy because the payment of an insurance claim does not compensate the owner for loss of business and employment or his inability to execute contracts. In most cases where major fires have occurred, the fire had a firm hold before the fire department was notified and the premises involved had been unoccupied at the time of the outbreak. Steady progress has been made in the field of automatic fire detection and a number of efficient systems for heat or smoke detection are at present available. It is essential however that, when considering the installation of an early warning system, the following general requirements be adhered to: The installation must be reliable in action for the whole of its effective working life, it should be capable of detecting an outbreak with a minimum loss of time and should incorporate mean whereby the location of the outbreak is indicated, it should sound the alarm at a point from which fire fighting resources can be speedily summoned, it should be insensitive to operation through causes other than those resulting from fire, it should not be affected by normal variation in atmospheric temperatures or by conditions caused by processes carried on within the protected area, and it should provide for the shut-down of any ventilating system.

The two general categories under which early fire warning devices fall are: (a) smoke detection and (b) heat detection. One smoke detection system embodies an ionisation chamber. When smoke passes through the chamber the radiation from the radium in the detector is absorbed and this triggers the alarm. In another system, a photo-electric cell detects the particles of carbonaceous origin passing through the sampling device and sets off the alarm. Smoke detector systems are used in aircraft, ship's holds, broadcast and television studios and for enclosed electronic equipment.

Because hot air rises at approximately 160-220 f.p.m., which is about three times that of smoke, the heat detector systems are sometimes preferred, depend-ing on the circumstances under which they are installed. Two types of heat detectors are available. The one is sensitive to the rate of rise in temperature, the other operates when a pre-determined temperature is reached. Both types are installed in one of Johan-nesburg's new theatres. The complete system com-prises differential, pressure wave and fusible link detectors which are connected to a sector control panel from where there is a direct extension to the fire station. The building is divided into sectors that are protected by several of the two types of detectors.

The rate of temperature rise or differential detector has a sensitive bi-metal strip which when heated bends until contact is made and the alarm is set off. It is set to operate at a rate of temperature rise of 10°F per minute. If the increase is below this rate, the alarm is set off when the temperature reaches 147°F. The pressure wave detector, also of the rate of temperature rise type, consists of a diaphragm that is connected to the end of a 150 ft length of 3/16 in diameter 24 S.W.G. copper tubing, the other end having bellows for testing. The diaphragm has a calibrated adjustment for pressures from 1/8 in to 1 in W.G. and the device normally is set to operate at a rate of rising in temperature of 6 to 8°F per minute. A by-pas valve prevents operation when the rate of temperature rise is under 6°F per minute. When the air in the tube expands, it moves the membrane against a contact which makes the alarm circuit. The fusible link detector operates when the temperature reaches 147°F. The detectors are spaced 5 ft apart and are interconnected with a length of stainless steel wire which terminates in a weighted contact. When any link fuses, this contact closes and sets off the alarm. The 12V d.c. the sector control panel is fitted with an automatic 120° phase loading rectifier with the incorporated thermic fuse for failure warning, a supervising circuit and charging switches, a voltage relay with a signal lamp and an audible warning device in case of a power failure and operating through the return circuit from the battery supply, twelve independent sector units with. 3-way .switches for 'off,' 'testing' and 'on,' and warring devices for battery fuse failure. The layout of the panel is illustrated in Fig 13.

8. CONCLUSION

For centuries the problem of the fire has cut across every field of human activity and the destruction left m Its wake represents quite a slice out of the national budget. With the advancing times, problems facing the fire fighting services grow ever more complex. The limitation of damage and destruction by fire is becoming increasingly important to the community. It is discouraging to note that in this country, with the exception of a few major centers, the fire service as a whole is sadly lacking in modern equipment. Only after some disaster has occurred where little or no fire protection existed is a move made to establish what is at most a token fire fighting force. The lack of reasonable fire fighting services in most of the smaller towns can be attributed to the high cost of maintenance and to the fact that towns are not compelled by ordinance to establish a fire department. This results in the lack of coordination which is considered necessary between towns and has the effect of splitting the available resources and reducing the potential strength of the service. Fire fighting services should be organized on a national basis so that equipment can be placed strategically to the best advantage. In the event of a fire, all nearby resources of equipment and men than can be brought to deal with the outbreak without any formalities. The production in this country of new and more efficient fire fighting equipment is not justified because the demand is not great enough. Fortunately, there is a wide range of equipment available from other countries but the policy of development and research is dictated by these countries as a result.