FIRE EXTINGUISHERS, use & Selection


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Posted by Paul (in NY) on Friday, September 20, 2002 at 11:12AM :

The Suppression of fire is a complex issue. To understand suppression, one must understand the elements that can be used in extinguishment. We have always been taught the "Fire Triangle", Heat, Oxygen, Fuel, remove any one of these and the fire will be extingusihed, remember the Boy Scouts fire triangle ? This was accepted and taught, but did not explain why dry chemical agents and halogenated (halon) agents worked in fire suppression. If you read Fire Protection Text Books as late as 1980's, they state that the process of extinguishment by these agents is not fully understood. Now thru research and technology, it is known that there is a 4th side to the Fire Triangle. This 4th side is "Chain Reaction of Combustion Process. If this 4th side is removed, fire will also be extinguished. With that in mind, lets look at Fire Extinguishers, type, the method of extinguishment, and selection.

Class of Fire;
Class A fire is standard Combustibles, paper, seats, rugs etc, etc

Class B Fire is Electrical (not the burning insulation, thats Class A)

Class C Fire is Combustible/flammable Liquids (Hydrocarbon & Polar Solvents)

Class D Fire is Burning Metal

In our Power Wagons and normal vehicles we face Class A,B, and C fires.

Extinguishers;
PRESURE WATER is rated Class A ONLY. It extinguishes fire by cooling below the ignition point and the fire will go out. Never use on Combustible/Flammable Liquids as a flowing fuel fire may result. Never use on Electrical fires
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DRY CHEMICAL Can be Rated Class A, B, C depending on the chemical used.
The method of extinguishment is by Breaking the Chain Reaction of Combustion Process. They DO NOT SMOTHER THE FIRE !!!, No Oxygen is removed, no fuel is removed, the material is not cooled.

Standard over the counter dry chemical extinguishers contain Sodium Bicarbonate. This will be effective on Class B & C fires

Purple K extinguishers contain Potassium Bicarbonate, and is MOST effective on Class C fires and good on Class B fires.

Dry Chemical extinguishers Rated for Class A,B,C, fires contain Monoammonium Phosphate. This agent still extinguishes by breaking the chain reaction, but also when heated the powder becomes sticky and does help seal the surface of Class A materials to prevent a burn back. Very DIRTY, will cause corrosion on metal and electrical parts. There are many other dry chemical agents, but the above mentioned are most popular. All Dry Chemical agents are DIRTY and cause Corrision on metal and electrical parts.
*********************************************CARBON DIOXIDE, C02. The method of extinguishment is by removal of oxygen.
The C02 enters the area and displaces oxygen. C02 is inert and will not propagate fire, thus it goes out. There is also a SMALL cooling effect. VERY CLEAN, Effective in small confined areas with NO WIND BLOWING. Any wind and the C02 will be blown away and oxygen will re enter. Large amounts needed to control fire. Minimum size for a truck, 15 to 20 pounds.
*********************************************HALOGENATED AGENTS;
Did you know that the old hand operated, pump, Carbon Tetrachloride fire extinguishers were in the Halon Family. The by products from Carbon Tetrachloride will kill you dead. They are no longer used or made. If you have one for display in your truck, EMPTY it, DONT EVER USE IT !!!!!
Halon Extinguishers work by chain breaking the Chain Reaction of the Combustion Process, they are SUPER EFFECTIVE, FAST, VERY CLEAN, but require a confined area to build up high concentrations of halon to extinguish the fire.

Halon 1301, Bromotrifluoromethane, Safe, used in Extinguishers and Computer Rooms

Halon 1211, Bromochlorodifluoromethane, Fast, Most used in Military, Health ???

Halon 2402, Dibromotetrafluoroethame, Fast, Mostly Miltary, health ????

The Montreal Protocall of 2000, which the USA was a signer, provides for the phase out of Halon due to the Ozone destroying effects. Halon is no longer being made in quanity for extinguishment agents. That in use can be used, recycled/sold.
Many large Chemical Companies have now developed new Chain Breaking agents which will retrofit to existing Halon Systems. These are SAFE Agents both for People and the Enviroment. There are MANY variables in Halon xxxx applications that will not be discussed in this application.
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To sum up, A PRESURE WATER extinguisher WILL NOT extinguish a gasoline fire, it can not cool below the flash point of gasoline which is roughly -55 degrees F depending on additives, it will not smother (remove oxygen), will not chain break, will not remove fuel. A PURPLE K Dry Chemical extinguisher will provide maximum effective knock down for your flammable/combustible liquid fires, POOR, POOR for
your Class A fires where Big Birtha drops her cigar down between your seats.

A DRY CHEMICAL CLASS A,B,C (usually painted WHITE) will extinguish your flammable/combustible liquid fires and Big Birtha's cigar in your seat. I would recommend a minimum size of 5 pounds and better a 10 pound size, 2 POUNDERS DONT APPLY. When you go to buy a Class A,B,C Dry Chemical Extinguisher, READ THE LABEL, dont buy it unless its UL Listed. If it has a UL Listed Plastic Valve, its going to be NON REFILLABLE one time throw away. Pay more and you will get a UL Listed Metal Valve that can be refilled. Make sure it has a Guage so you can be sure the propellent charge has not leaked out. IF YOU FIRE THE EXTINGUISHER, IT MUST BE REFILLED, no matter how little you discharged. Power will stay on the valve seat and the proplellent charge will leak.
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FOAM AGENTS are beyond the scope of this discussion
*********************************************This has not even scratched the surface of extinguishing agents, their use and applications and joint applications. Fire Suppression is a complex subject. My background in Fire Protection began in 1960. I hold my Degree in Fire Protection
Engineering/Suppression. I am a retired Municiple Chief of Department, Retired
Industrial Chief of Department, New York State Certified Fire Training Officer,
Now retired, I continue to teach Flammable Liquid Fire Suppression, with some of my clients being Griffiss Air Force Base CFR, The IBM Corp, New York State Academy of Fire Science, Municiple Fire Departments...........and of course following the family business, Maple Syrup. I dont want to take any more of Joe's bandwith here, but will answer any questions if you email me direct. You are probably only armed with one small fire extinguisher, you have to know when to exercise FIGHT or FLIGHT. Talk to your local Fire Department, see if they offer fire extinguisher training, if so, take the class, your life may depend on what you learn.

Paul





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