how fire extinguishers put fires out?

Question

hi everyone, this is abit tecnical this one, ive got an assignment at college in hairdressing and need to know about four fire extinguishers, what they put out and how they put them out, and which ones i shouldnt use on certain materials. Ive been on loads of websites im struggling to find HOW they put them out can anyone help?The extinguishers are foam, carbon dioxide, water and dry powder.
Cheers x

Answer 1

Fire is a chemcial process involving fuel, heat, and oxygen. Fire can be extinguished by halting the chemical process directly, or removing one of those three base components.

Most extinguishers work by cooling the fire and/or removing the oxygen from the equation.

Just as there are different types of fire extinguishers, there are different types of fires. In the U.S. fires are broken down in to five classes. Keep in mind that a fire can involve multiple classes simultaneously.

CLASS A - Fires involving Wood, Paper, or Trash

CLASS B - Fires involving flammable liquids and gases

CLASS C - Fires involving energized electrical equipment

CLASS D - Fires involving flammable metals.

CLASS K - Fires involving cooking oils.

About the extinguishers you asked about...

Foam - (Suitable for Class A & B Fires) has a cooling effect and "blankets" the fuel creating a physical barrier separating the oygen fromt he process. Do NOT use this extinguisher on a Class C Fire as the foam agent is water based and will conduct electricity. The water based agent can also be dangerious on cooking oil fires (class K) because of the high water content, it may splatter and injure the user. Foam is not suitable for Class D Fires.

Carbon Dioxide - (Suitable for Class B & C Fires) also has a cooling effect, but it's main function is tempoarily displacing the Oxygen. CO2 can "knock down" the flames on a class A or K fire, but most likely the fire will re-ignite once the CO2 dissapates. CO2 is not effective on class D fires.

Water - (Suitable for Class A fires only) extinguishing the fire by cooling it. Water is very dangerous to use on all other types of fires because water conducts electricity, and will spatter/spread flammable liquids and cooking oils, and water only aggrivates a class D fire.

Dry Chemical (not to be confused with dry powder is suitable for Class B & C fires, and if it's the ABC Dry Chemical, Class A as well.) - extinguishes the fire by blanketing the fuel and thus preventing the oxygen from getting to the fire. Dry Chemcial agents are the most common type of portable fire extinguisher as most are chaged with the ABC chemical and are suitable for the three most common classes of fire. ABC should not be used to extinguish a cooking oil fire in a restaurant application as the ABC chemcial is not compatable with the automatic extinguishing systems most resaurants have.

Dry Powder (which I don't think you meant, is for CLASS D fires) and reacts with the heat to create an crust over the fire and the flammable metals involved will stop burning due to lack of oxygen. Class D fire extinguishers will have no effect on the other 4 classes of fire.

There are a variety of other types of fire extinguishers too, including, but not limited to, Potasium based, organic salt based, halogenated agents...

For more information on all fire extinguishers, the classes of fire, and how extinguishers work, visit the following excellent site...

Answer 2

No, but it would be appropriate to pee on the fire in your toilet to put it out - the fire extinguisher foam would just clog up your pipes and also leave you with one heck of a big mess on your hands.

Answer 3

There are four types of fires:
Paper/trash/wood and other more-or-less organic solids. "Ordinary combustibles."
Inflammable liquids such as gasoline or paint thinner.
Electrical fires, with electricity still flowing to the burning equipment.
Burning reactive metals, such as sodium, magnesium, titanium, and so forth. Such metals not only burn at high temperatures but can chemically extract oxygen from water and even carbon dioxide. Pyrophoric materials such as organoboron, organolithium and organomagnesium (Grignard) compounds are also in Class D because they react violently with water and carbon dioxide.
There are six common types of fire extinguishers: Type A This is a pressurized-water extinguisher and works by removing heat. The fire's heat goes into heating and evaporating the water, which has a very high heat capacity, and soaking the burning materials with enough water will cool them to below the combustion point. However, all burning materials have to be soaked down or the fire will restart. These extinguishers cannot be used for Type B fires because burning organic liquids will float on water while continuing to burn. They should not be used for Type C fires because of the risk of electrical shock, nor for Type D fires because water will support the combustion of Type D materials. Type A extinguishers are normally silver.
CO2 The high-pressure CO2 extinguisher removes oxygen and, to a certain extent, heat. The expanding CO2 cools, sometimes enough to produce dry ice snow, but the main effect is to blanket the burning material with a heavy gas that cannot support combustion. CO2 extinguishers leave no residue and so are especially suitable for extinguishing Type C fires, which often involve delicate equipment. CO2 extinguishers are not suitable for use on Type A fires because the extinguished materials usually retain enough heat to re-ignite when the CO2 dissipates; nor for Type D fires because CO2 will support the combustion of Type D materials. CO2 extinguishers are normally red and have large nozzles.
Halon (ABC) Halon extinguishers normally contain bromochlorodifluoromethane, a very heavy gas (much heavier than CO2). This not only displaces oxygen from around the fire but chemically reacts in a way that shuts down combustion. (It decomposes into chlorine and bromine radicals, which scavenge hydrogen radicals essential for keeping combustion going.) Halon extinguishers, like CO2 extinguishers, are especially suitable for Type C fires and delicate equipment, but because they chemically shut down combustion they are also good for Type A fires. They are being phased out because of the damage chlorofluorocarbons do to the ozone layer.
Type BC The BC dry-chemical extinguisher is filled with sodium or potassium carbonate. It isolates the burning material from oxygen, but enough heat can convert the solid carbonate into CO2 gas and so this type of extinguisher should NOT be used for Type A or Type D fires. Dry-chemical extinguishers are normally red, with small nozzles (and sometimes hoses).
Type ABC The ABC dry-chemical extinguisher is filled with ammonium phosphate. It isolates the burning material from oxygen, but burning Class D materials can liberate oxygen from the phosphate ion and so this type of extinguisher should NOT be used for Type D fires. Dry-chemical extinguishers are normally red, with small nozzles (and sometimes hozes).
Type D The cheap version of this is a bucket of sand, which isolates the Type D combustible from oxygen. Sand is silicon dioxide, which is too stable to liberate oxygen. Commercial Type D extinguishers are filled with materials which are even more stable than sand.

Answer 4

They work by depriving the fire of oxygen.

Answer 5

They exclude O2 from the fire....