Most of the following is what I remember from military training.

The basic fire classes are class A, B, C, and D.

Class A fires are considered to be "Anything that leaves an ash". This class includes wood, paper, plastics, rubber, and so on. many extinguishing agents can be used for these. The most universal of all is of course water. The principal plan of attack to put out a class A is to cool the ignition source, penetrate into the center of the burning mass so that embers cannot hide out and wait a chance to reflash, pull apart the materials and ensure that all embers or coals have been put out, and then post a reflash watch to keep an eye on whatever it was until there is no chance of the material(s) catching on fire again from a hidden ember. This is what reflash IS - the action of the fire restarting due to an ignition source that was not completely extinguished.

Class B is Flammable Liquids. It can be anything - gas, oil, solvents, paint, you name it. It's very important with this class of fire to find out what the fluid is that is on fire. Many solvents produce harmful byproducts when they burn, and some substances are ten times more dangerous when they combine with other chemicals.

Additionally - care must be taken to avoid splashing burning liquids onto anything else that may also be combustible. A small grease fire in a pan on the stove can involve and consume the whole kitchen or house if a CO2 extinguisher sprays the burning grease all over the room. THAT one I have seen before in an apartment, or at least the aftermath...

Not only CO2, but water and various foam agents can control a liquid fire.

Class C or "Charlie" fires are those caused by electricity. THE MOST CRITICAL ELEMENT IN CONTROLLING A CLASS CHARLIE FIRE IS TO REMOVE THE SOURCE OF POWER. Failure to turn off or disconnect power will result in a never ending ignition source.

ALWAYS ASSUME POWER IS CONNECTED! In using a CO2 bottle on a class charlie fire, KEEP THE BOTTOM OF THE EXTINGUISHER GROUNDED AT ALL TIMES. Carbon conducts electricity, and CO2 is CARBON DIOXIDE. Q.E.D.:The stream of extinguishing agent can and will conduct electricity. By grounding the bottle you remove yourself from the path of conductivety, just like the third prong on an electric cord is designed to do.

Class D's are rare, these are metals fires. Certain types of metal and alloy will burn, notably magnesium or alloy castings with a high enough percentage of magnesium in them. Volkswagen engine casings are a perfect example.

The worst thing to do when magnesium alloy is involved is to spray water on it, because the water will act as an oxidizer and cause the fire to intensify like you wouldn't believe!

Try this sometime:
Get a bad VW casing, light it on fire at some spot on it, and then drop it into a lake or river. You will find that from a small area that is barely glowing the fire will instantly become a flaring, spark throwing, flash-bulb intensity inferno.

Metals are difficult to extinguish, although there are some specialised agents available for this. The normal procedure is to isolate the affected material and allow it to burn out, or in the case of ships at sea - jettison the item over the side.

There is substantial risk of blindness when dealing with this class of fire, because of the flare of light when metals have enough oxygen as they burn.


Basic combustion theory is the fire triangle. A fire needs three things combined in order to happen:

1)Fuel
2)Oxygen
and
3)Heat

The removal of any one of these elements is enough to put out a fire.

If we remove the fuel, it cannot burn.
If we remove the oxygen (this is what a CO2 bottle does) it cannot burn.
If we remove the HEAT the fire cannot burn. - This is what is happening when we apply water to a fire, we attempt to cool the blaze down to less than it's ignition point and keep it there.

This may not seem to apply to electrical fires, but the electricity in most class charlie fires serves to provide a heat source. The insulation of the wires and the surrounding materials then provide the fuel, and with enough oxygen there ya go!

Halon was developed to remove the oxygen in electronics spaces without creating a mess by leaving a residue. It is designed to displace oxygen, and as such we need to be careful that we don't cut off our own oxygen supply when using Halon on a fire.

That's it in a nutshell - I hope this helps somebody some day.
If my ten minutes of typing saves even one person from death or injury, or reduces somebodies property damage, then it was well worth the trouble!

~Wolf

 

Very good and informative. They have updated the fire triangle though and it is now a Tetrahedron. The four things for a fire to burn are:

A) Fuel
B) Heat
C) Oxidizing Agent (Oxygen)
D) Self Sustained Chemical Reaction

Also, I believe aluminum is a metal that is in the class D catagory. You don't want to use water on a class D fire because it could decompose the water and release flammable hydrogen gas. Also a metal fire may burn bright to start with then look like it is out but still be burning - at over 2000 degrees F.

Ok, I'll admit that I had to look in my Firefighter Essentials book for the last paragraph of info, but I thought it could be useful. It's a good idea to carry an A,B,C extinguisher fire in your vehicle because you may need it or come upon a car fire sometime.

 

>Class D's are rare, these are metals fires. Certain types of
>metal and alloy will burn, notably magnesium or alloy
>castings with a high enough percentage of magnesium in them.
>Volkswagen engine casings are a perfect example.
>
>The worst thing to do when magnesium alloy is involved is to
>spray water on it, because the water will act as an oxidizer
>and cause the fire to intensify like you wouldn't believe!
>

Over the summer at work I actually managed to start a titainium fire. It causes a flash fire just like magnesium. What happened was I was grinding a point on the end of a 12 foot 5/16 diameter titainium bar. The sparks come off instantly hot and bright like a sparkler. Well there was a hopper right by me filled with titanium shavings from a part that we make out of the bars. The shavings also had some oil on them. The sparks went into the chip barrel or hopper and instantly lit the shavings on fire. In no more than 2 seconds the fire had reached 5 feet in height. A guy I work with said I looked like the tazmanian devil running for the fire extinguisher. All I know is that we have dry chemical extinguishers at work. It took a little bit but it put the fire out and we got a nice break while we waited for the shop to air out.

I am not sure about aluminum being flammable. I am sure everthing has the potential of starting on fire but some times we can run aluminum without coolant. I suppose I could always try to start an aluminum fire.

 

>
>I am not sure about aluminum being flammable. I am sure
>everthing has the potential of starting on fire but some
>times we can run aluminum without coolant. I suppose I
>could always try to start an aluminum fire.

As an EMT we are using brass regulators on our Oxygen bottles because of the tendency of the aluminum regulators to catch fire due to the high pressure of the O2 canister. As you can imagine a fire with a compressed source of oxygen is bad!!

 

i have seen aluminum catch on fire, but it's always been small and usually due to welding or working on the part. never because of machining it, even without lube.

halon fire extingushers are now illegal, they are being removed for service, and should be replaced by another substance.. (too bad, they worked great)

 

>All I know is that we have dry chemical
>extinguishers at work. It took a little bit but it put the
>fire out and we got a nice break while we waited for the
>shop to air out.
>

You might want to check to see if it is a class D extinguisher. I would imagine if you're working with those kinds of metals they would have one.

 

A cloud of Halon or Argon, or even CO2 will kill you before you realize you are in it. They all displace oxygen both in the air and in your bloodstream. Also, if you ever do encounter a car fire, be it your own, or someone else, watch the A/C system. If it has R-12, when it burns, it will release Phosgene(?) gas, also brutally deadly.

Jared

 

Hey Fordrancher, ever here of the fire pentigon?
fuel
heat
oxygen
sustained chemical reaction
fire chief
Remove any one and the fire goes out

 

> Hey Fordrancher, ever here of the fire pentigon?
> fuel
> heat
> oxygen
> sustained chemical reaction
> fire chief
> Remove any one and the fire goes out

hahahahaha..... now that's a good one..... doesn't work though... our cheif always hides when were at a fire... and that never seems to help it go out....

 

 

Hey 1-Ton you beat me to it, I was going to post the pentagon but you beat me to it. However it does work quite well in my department. However chief means any chief not just chief of the department, if you remove battalion or division chiefs it is just as effective as removing chief of the department. Greywolf, great post you are right on target with your information.
T.Roberts
UFD Local 1147

 

> Hey Fordrancher, ever here of the fire pentigon?
> fuel
> heat
> oxygen
> sustained chemical reaction
> fire chief
> Remove any one and the fire goes out


I have heard that one and even typed it up and posted signs around the firehall Also another good one is

C heif
H as
A rived
O n
S cene

 

[updated:LAST EDITED ON 02-Dec-02 AT 06:21 AM (EST)]All jokes aside, Greywolf is right on.
I would like to add that EVERONE needs to have smoke detectors in their homes. They truly do save lives!!

I am always surprised,and soberd(and I am sure the rest of you firefighters will agree), when we have live burn trainings, how fast a house will become fully involved. It is real scary to think how little time you would have to get all of your family out before it is too late