Ch6 Fire Extinguishers Flashcards
Portable fire extinguishers are often suitable to extinguish more than one class of fire while some are only designed for a particular class of fire… p254
There are five classes of portable fire extinguishers to match five classes of fires: Class A, B, C, D, and K.
Class C extinguishing agents will not conduct electricity which makes them suitable for electrical fires… p256
Water and water based agents conduct electricity and cannot be used on Class C fires until the electricity has been turned off.
A portable fire extinguisher should be used only for the fire type or types for which it is intended.
The appropriate portable fire extinguisher to use on a given fire depends on what is burning.
Water and water based agents conduct electricity and cannot be used until the electricity has been shut off.
True.
However, Stored pressure water mist extinguishers use deionized water as the agent and nozzles that produce a fine mist instead of a solid stream. Impurities in water conduct electricity, deionization is what makes these Class A extinguishers safe to use on Class C fires.
When using AFFF, the operator should NOT apply foam directly on the fuel.
Instead, allow it to rain down on to the fuel’s surface or deflect the foam off a nearby object of surface.
Clean agent extinguishers are non-conductive and can extinguish electrical energized equipment.
Clean agents in halontron effectively cool and smother fires in Class A and B fuels and inhibit the sustained chemical reaction in Class C fires.
DRY CHEMICAL EXTINGUISHERS do not cake, the application of agents may result in a cloud of airborne particulate.
While the agents themselves are non-toxic and generally considered safe to use, the cloud may reduce visibility and create respiratory problems.
Fires involving Class D combustible metals require special dry powder extinguishing agents and application techniques. No single extinguishing agent will control or extinguish fires in all combustible metals; others extinguish fires in only one type of metal.
Operators should apply the agent gently to avoid breaking any crust that may form over the burning metal. If the crust breaks, the fire may flare and expose more uninvolved material to combustion. Avoid scattering the burning metal. Additional applications may be necessary to cover up any hot spots that develop.
Approach the fire from the upwind side (windward side); that is the wind at your back side.
This practice keeps you out of heated and toxic gases from the fire.
Portable fire extinguishers are identified in two ways. One system uses geometric shapes of specific colors with the class letter shown within the shape.
A with the green triangle is intended for ordinary combustibles. Ordinary combustibles are: wood, paper, plastic, rubber, and cloth.
B with the red square is intended for flammable and combustible liquids. These are hydrocarbons, alcohol based liquids, and gases that will support combustion.
C with the blue circle is intended for live electrical equipment.
D with the yellow star is intended for combustible metals. This can be magnesium, potassium, titanium, and zirconium.
K with the black hexagon is intended for cooking oils.
Extinguishing agents use at least one type of method to extinguish fires…
Smothering - excludes oxygen from the burning process.
Cooling - reduces the burning material below its ignition temperature.
Chemical flame inhibition - Interrupts the chemical chain reaction in the burning process.
Saponification - Forms an oxygen excluding soapy foam surface.
All portable fire extinguishers expel their contents using one of the following mechanisms…
Manual pump - the operator physically applies pressure to a pump that increases pressure within the container which forces the agent out a nozzle at the end of a hose.
Stored pressure - compressed air or inert gas within the container forces the agent out of a nozzle at the end of a hose when the operator presses the handle.
Pressure cartridge - a separate cartridge on the side of the container contains inert gas. When the operator punctures the cartridge seal, the expellant enters the container and forces the agent out of a nozzle at the end of a hose.
Carbon dioxide extinguishers store carbon dioxide under its own pressure as a liquified gas. The gaseous discharge usually forms dry ice crystals or carbon dioxide “snow”. Shortly after discharge, the snow changes from a solid to a gas without becoming a liquid (sublimation). The CO2 gas displaces oxygen and smothers the fire for extinguishment… p262
Wheeled CO2 units are considerably larger than handheld units. Wheeled units usually have 50-100 pound capacities. After operators wheel the unit to the fire, they must deploy or unwind the hose (usually 15 feet long) from the unit before use. Otherwise, the principal of operation is the same as that of a smaller handheld unit.
Clean Agent Extinguishers
Clean agent extinguishers effectively cool and smother fires in Class A and B fuels and inhibit the sustained chemical reaction in Class C fires. The agents are non-conductive and can extinguish energized equipment fires.
Wheeled Unit Extinguisher procedure…
After positioning the extinguishing unit at a fire, and before discharging any extinguishing agent, the operator should stretch out the hose completely.
