Fire Extinguisher Operation PDF

Unit A-4 • Introduction to Plant and Fire Safety OBJECTIVE 1 Describe the construction and operation of various types of portable fire extinguishers. FIRE EXTINGUISHER OPERATION CAUTION Additional hands-on training in fire extinguisher use is usually required at each place of employment. The m...

Unit A-4 • Introduction to Plant and Fire Safety OBJECTIVE 1 Describe the construction and operation of various types of portable fire extinguishers. FIRE EXTINGUISHER OPERATION CAUTION Additional hands-on training in fire extinguisher use is usually required at each place of employment. The most common instructions for using fire extinguishers involves the acronym PASS: P - Pull the pin A - Aim the nozzle S - Squeeze the handle S - Sweep the extinguisher spray at the fire Fire extinguishers are equipped with ring pins that lock the operating lever, to prevent accidental discharge. To operate an extinguisher: 1. Set it on the ground, hold the handle loosely in one hand (so as not to squeeze the handle and have the extinguishing agent blow out unintended), and pull out the ring pin with the other hand. 2. Move the unit to the best position. 3. Hold the hose in one hand, and squeeze the discharge lever with the other. 4. Aim the extinguisher at the base of the fire, and sweep the nozzle back and forth. Do not sweep too fast. Fire extinguishers are most effective when their spray lingers briefly when sweeping. 5-4 / S _ 4th Class Edition 3 • Part A Fire Extinguishing • Chapter 5 Figure 1 shows the general instructions found on a fire extinguisher, as well as, the class of fires that the extinguisher is suitable for. CONSTRUCTION AND OPERATION OF PORTABLE FIRE EXTINGUISHERS Approved fire extinguishers are grouped by their mechanical action of operation: 1. Stored-Pressure 2. Pump Tank 3. Self-Expelling 4. Cartridge or Cylinder Operated Stored-Pressure Type A common type of stored-pressure extinguisher contains 10 litres of water, and has a mass of about 14 kg. It can be operated intermittently, and is easily recharged. A stored-pressure extinguisher has a single chamber, which contains both the agent and the expellant gas. The cap, or head assembly, consists of a siphon tube, combination carrying handle/ operating lever, discharge valve, air pressure valve, pressure gauge, discharge hose, and nozzle. The stored-pressure water extinguisher is shown below. 4th Class Edition 3 • Part A 5-5 Unit A-4 • Introduction to Plant and Fire Safety ================== ================== Figure 2- Stored-Pressure Water Extinguisher The extinguisher is pressurized with compressed air or an inert gas. The pressure is in the range of 600 to 900 kPa. The air or gas is charged through a Schrader valve on the head. Another stored-pressure extinguisher is the Type K for ldtchen fires. Some dry chemical extinguishers are also of the stored-pressure type, with either a rechargeable or disposable shell. The disposable shell type has the agent and the expellant gas factory sealed. The shell is then screwed onto a valve and nozzle assembly. Some smaller extinguishers are of a throwaway type, where the entire device is disposed of after use, or after expiry. 5-6 ? S ....;..__ 4th Class Edition 3 • Part A _ Fire Extinguishing ================================ o Chapter 5 Figure 4 shows a dry chemical stored-pressure extinguisher. Figure 4- Dry Chemical Extinguisher Operating Lever -- Expellant Gas Dry Chemical Discharge Tube Nozzle Stored-Pressure Type The Aqueous Film Forming Foam (AFFF) type of extinguisher is suitable for water-soluble flammable liquids such as alcohols, acetone, esters, or ketones. The hand-held extinguisher is a stored-pressure type. One type has a liquid solution of AFFF in the tank. Another type has plain water in the tank, and a replaceable charge of solid AFFF in part of the nozzle. Both types have an air-aspirating nozzle. The two types are shown in the figure below. I Figure 5- AFFF Extinguishers - --- Discharge Lever ......._._ Carrying Handle ' ---{·<-------Pressure Gauge ' _..,... Discharge Lever ---Carrying Handle ---{·<------- Pressure Gauge :::U- Air Aspirating Foam Nozzle Premixed Solution -1+--t-- Solid Charge in Housing +-11---++-+---Air Aspirating Foam Nozzle +1--- Water Pump Tanks Two types of pump tanks are available: 1. Floor-Standing model 2. Backpack model 4th Class Edition 3 o Part A 5-7 Unit A-4 • Introduction to Plant and Fire Safety ==================== ==================== The floor-standing model shown in Figure 6 is a cylindrical tank, with carrying handles on the container or built into the pump handle. Lighter tanks have a hinged footrest so the tank does not move around as it empties. The tank capacity ranges from about 7 to 25 litres. The pump is a vertical piston type, mounted inside the cylinder. A short length of hose with a discharge nozzle is attached to the external part of the pump. To operate the pump: 1. Set the unit is set on the ground, and lower the foot rest. 2. To force water through the hose, pump the handle up and down with one hand, while holding the hose in the other hand. The disadvantage of this type of unit is that to move the unit, pumping must stop. Also, the force, range, and duration of water flow depends to some extent on the operator. The duration of operation ranges from 45 seconds to 180 seconds, depending on capacity. The range of the stream is 9 m to 12m. Figure 6- Floor-Standing Water Pump Tank Extinguisher Pump-------._ Carrying ----Handle Water or Anti-freez----..t Solution Hose The figure below shows the backpack pump type. The principle of operation is similar to the floor model, except that the pump is of the "trombone" type, and the discharge nozzle is mounted on the pump. The capacity is usually 10 litres, so that it can be easily carried. The performance and rating are the same as a floor-standing type of the same capacity. The trombone handle has a pump action to pressurize the line and force the water out onto the fire. Figure 7- Backpack Water Pump Extinguisher Trombone Type Pump Hose .--------Carrying Handle Shoulder Straps s-a 7------------------------ s: 4th Class Edition 3 • Part A Fire Extinguishing o Chapter 5 Self-Expelling C02 fire extinguishers are self-expelling. The extinguishing agent, confined in liquid and gaseous form, is also the pressurizing agent. When released from the extinguisher, C02 displaces oxygen in the vicinity of discharge to the point where combustion cannot be supported. The rapid expansion from a liquid to a gas, when the C02 discharges, converts about 30% of the liquid into dry ice, which then sublimes (evaporates directly) into a gas. Carbon dioxide extinguishers have a short range, because the agent is expelled in the form of a cloud, which is a mixture of gaseous and solid C02 . The extinguisher consists of a pressure cylinder (or shell), a siphon tube, and a valve to release the agent. Connected to the valve is a discharge "horn;' or a horn and hose combination. The siphon tube extends from the valve to almost the bottom of the cylinder. Normally only liquid C02 reaches the discharge horn. After about 80% of the cylinder contents have been discharged, the remainder enters the siphon tube as a gas. A typical carbon dioxide extinguisher is shown in Figure 8. Figure 8- C02 Extinguisher == Siphon +-H-Operating Lever ,1-- 1 Tube Discharge Horn (a) (b) The smaller hand-held models often have the horn directly connected to the valve assembly with a metal tube swing joint connector. Larger models have the discharge horn connected to the valve by a short length of hose. The extinguisher is discharged by squeezing the operating lever. Touching the discharge horn during operation should be avoided, as it is likely to be very cold. To extinguish flammable liquid fires, start at the nearest edge of the fire, and sweep from side-toside, towards the back of the fire. Another method that can be used is called overhead application. In this method, point the discharge horn down, at an angle of about 45°, towards the centre of the burning area. Usually the horn is not moved. If the surface on fire is a large pool of oil on a floor space, be careful when progressing into the room. Flames from burning liquids can spread and reignite surfaces that have already been extinguished. This will block the means of egress. The side-to-side sweeping method is likely to give better results on spill fires. The overhead method may be better on confined fires. 4th Class Edition 3 o Part A 5-9 Unit A-4 • Introduction to Plant and Fire Safety ==================== ================== For electrical equipment fires, direct the discharge at the source of the flames. The equipment should be de-energized as soon as possible to prevent possible re-ignition. The Halotron I Clean Agent extinguishing medium is effective on Class A, B, and C fires. It does not conduct electricity, and it is not corrosive. As well, this pressurized halocarbon agent is environmentally acceptable. Despite its name, it does not contain halon. It discharges as a rapidly evaporating liquid, with a higher boiling temperature than other fire-fighting liquids under pressure (at 27°C in the atmosphere). Because Halotron I retains its liquid state longer, it permits for a greater distance_ of travel (1.8- 13.7 metres), before turning into a gas. Cartridge or Cylinder Operated Dry chemical extinguishers can also be cartridge type. One design uses a cartridge of carbon dioxide or nitrogen to expel the agent. In this type of extinguisher, the cartridge can be either internal or external. The expellant gas is released to the bottom of the shell when the puncture lever is depressed, forcing the dry chemical out the nozzle. The rate of flow of dry chemical agent can be controlled by squeezing the operating lever at the nozzle on the end of the hose. Figure 9- How to use the Cartridge Type Dry Chemical Extinguisher 1 If so equipped, remove ring pin. Remove hose. Squeeze nozzle operating lever. Direct stream at base of flames using a side to side motion. if.' 2 4 Push down on puncture lever. After using: Invert extinguisher by grasping elbow, and squeeze nozzle to release all pressure. Larger capacity AFFF extinguishers are of the wheeled type. They have a separate cylinder of nitrogen to pressurize the agent container. The discharge is controlled by a special type of aspirating nozzle at the end of the hose assembly. The aspirating nozzle induces air into the water/ agent solution. The mixing of the air and solution causes the solution to form a foam. 5-10 7------------------------- s: 4th Class Edition 3 • Part A Fire Extinguishing • Chapter 5 ================================ == On a flammable liquid fire of a depth that is more than 6 mm, such as in a large tank, the best results are obtained when the discharge is directed against the back wall of the tank. Aim the flow of foam to just above the burning surface, to permit the natural spread of the foam back over the burning liquid. If this is not possible, stand far enough away from the fire to allow the foam to fall lightly on the burning surface. Do not allow the foam to splash into the burning liquid. If possible, move around the fire while directing the foam stream. This will give maximum coverage while the extinguisher is discharging. For flammable liquid fires, direct the foam over the burning surface by bouncing it off the floor just in front of the burning area. Dry powder agent can be deployed on a fire in many ways. The agent, extinguisher, and method of application should be selected in accordance with the manufacturer's recommendations. The powder may be applied to the fire by means of an extinguisher, using a C02 cartridge - as the expellant, or from cardboard tubes or metal pails by means of a scoop or shovel. The agent should be applied so that it covers the fire and provides a smothering blanket. Additional agent may be required for hot spots. Care should be taken not to scatter the fire. The fire should be left undisturbed until it has cooled. A dry powder extinguisher is shown in Figure 10. Figure 10- Dry Powder Extinguisher Puncture Lever Carrying -Handle Gas Tube Dry Powder -------L Extinguishing combustible metal fires involves hazards such as high temperatures, steam explosions, hydrogen explosions, and toxic products of combustion. If common extinguishing agents are used, explosive reactions may occur. 4th Class Edition 3 • Part A 5-11