FIRE EXTINGUISHERS

We know what they do, we know….uh, well….we know what they do.  In reality, we actually know very little about fire extinguishers.  We know they extinguish fires but there are other important things to learn about fire extinguishers that will help us.

  We will start with the basics.  Instructors use a triangle to describe the science of fire. The three legs of the triangle represent the three parts needed for fire to exist.  If one of the legs is removed from the triangle, it is no longer a triangle.  If one of the parts of fire is removed, it is no longer a fire.  These three parts need to be in the right combination.  The parts are heat, fuel, and oxygen.  There is one more aspect called a chemical chain reaction that sustains fire and makes it grow.

    There is an interesting fact about fires.  Did you know that fire is the same as rust?  Well, not literally, of course, but they are the same process. Fire produces heat, so does rust, we just don’t feel it in rust.  Fire reduces fuels to ashes, rust reduces metal to dust.  The process is calledoxidation.  Fire is very rapid and rust is very slow.

When we talk about heat, we mean the heat that may have caused the fire and the heat the fire produces.  The heat that causes the fire can be small in size, like lighters, candles, matches, woodstoves, ovens, and space heaters, butthe heat a fire produces is tremendous.  This tremendous heat builds from an initial 150 degrees to over 1100 degrees in a room on fire and has a domino effect on the whole process.  The more heat the fire produces, the faster and easier things are destroyed by it.  Let me describe it this way, a fire will travel faster UP a hill than down it.  Now, the physics I learned is that anythinwill travel downhill faster than uphill, something to do with gravity.  But the heat a fire produces preheats the fuel (we will discuss this later) in front of it, so the brush, trees, and grass on a hill gets pre-burned. 

We can deal with the heat in two ways, before and after.  Dealing with the heat before includes kitchen fire safety, which I recently wrote about.  Safe use of candles, as well as space heaters, is also important.   Dealing with the heat after includes removing the heat to put the fire out.  That is one way the extinguisher works.  The powder it contains removes the heat by absorption and by replacing the super heated air with cool, fresh air.

    The fuel part of fire can be very diverse.  It is what the scientists call combustible materials or flammable liquids.  Materials can be described as those that leave an ash when burned.  We know combustible materials as plain old ordinary stuff.  Couches, wood paneling, dried paint on the walls, curtains, carpets, dressers, television sets, appliances and just about anything else in our homes.  Liquids are petroleum based products that don’t leave an ash when burned.  We know flammable liquids as gas, propane, mineral spirits, and solvents.  We can remove the fuel from a fire by simply keeping things neat and tidy.  I have been into homes that have stacks of old newspapers all over.

These are loads of fuel.  I have also been into homes that have basements filled with fire wood.  LOTS of fuel!  An extinguisher removes the fuel by covering it with a powder and by replacing the oxygen.

The third part of the fire triangle is oxygen.  It seems as though it may be the most difficult part to remove since it is all around us and so abundant. But, in reality, it is pretty easy to remove.  Have you ever been told to sleep with your door closed at night?  This creates little compartments out ofyour home.  This separates a fire from the oxygen in other compartments. I have seen fires in a bedroom that have burned themselves out of oxygen and out of business.  I have been to fires that began in the basement and did major structural damage, yet the only indication of a fire was a slight smoke smell on the main floor, all because the basement door was closed.

There is a very dangerous aspect of closed doors and fire that I have to mention.  Have you watched the movie called "Back Draft"?  This movie is about an arsonist who specializes in creating back drafts.  A back draft phenomenon occurs when a fire in a closed atmosphere has burned away almost all of the oxygen.  The fire is in a smoldering state and the whole room and contents are superheated, even the air and gases.  The back draft occurs when oxygen is re-introduced back into the atmosphere.  Everything in the room ignites all at once with enough force to kill.

 The best way to avoid back draft situations is to follow a good escape plan and get out.  Oxygen can also be dealt with before and after.  We see that closing doors deals with it before and the extinguisher deals with it after.  It replaces the oxygen with either carbon dioxide or smothers it so no oxygen can get to the fire.

We need to classify the types of fuel in order to understand the types of extinguishers.  Would you bring a basketball to a soccer game?  Not all balls are the same even though they look alike.  Not all extinguishers are the same even though they look alike.  We discussed two of the classes of fuels earlier, combustible materials, or class A fuels, and flammable liquids, or class B fuels.  Class C fuels are energized electrical equipment.  It is considered class C until the power is disconnected, then it becomes either a class A or B fuel. Class D fires involve combustible metals.  Yes, metal burns, or more correctly, the vapors from the superheated metal (oxidation process) burns.   Can yourecall the VW Bugs of the 1960’s?  If you owned one, you had a combustible metal parked in your garage.  The engine blocks of the early VW’s  were cast from magnesium.  Magnesium is pretty neat to see burn.  Imagine the surprise of many a fire fighter when they apply water to that burning VW!  You see, magnesium on fire reacts violently with water and produces the exact opposite effectyou would expect, very bright light and tremendous flames.  So you see how important the classification of fuels is concerning the different types of extinguishers.

There are three common types of extinguishers.  Knowing the classes of fuels and the types of extinguishers, you will have the knowledge you need to purchase the correct extinguisher for your home.  There are several more types, but you don’t have a manufacturing plant in your home, so you don’t need to know about extinguishers you may never see. 

All fire extinguishers have a pictograph, or a picture, of what they can be used for.  A class A extinguisher has a picture of a garbage can on fire.  Class B extinguishers have a picture of a gas can on fire.  They may also have pictures with a line through it to show what classes of fire they shouldn’t be used on.

The first type of extinguisher is called the water or APW (Air Pressurized Water) extinguisher.  A very big squirt gun, really.  It has a pressure gauge and a small diameter hose.  Nitrogen is usually used as the propellant.  This extinguisher is to be used on class A fires only.

Obviously, water on class C fires, electrical fires, is dangerous and it will only spread a class B fire, a liquid fuel fire.  This type of extinguisher works by cooling the fire or removing the heat.

The second type of extinguisher is a carbon dioxide extinguisher.  It doesn’t have a pressure gauge and has a large bell shaped nozzle.  This type of extinguisher is not filled to a certain pressure like those with gauges but by weight.  The nozzle is designed to spread the carbon dioxide over the fire better. This type of extinguisher works by replacing the oxygen with the carbon dioxide or removing the oxygen.  Use this type on Class B and C fires.

The last type, the most common, is called a dry chemical extinguisher.   It has a small diameter hose and a pressure gauge.  It is filled with a dry, whitish/yellowish powder and usually nitrogen.  Have you ever suffered from heart-burn?  This type of extinguisher is like a giant Rolaids or Tums because the powder is sodium based.  It does contain a fire retardant but it is relatively harmless.  Relatively only because you don’t consume it or breath it constantly. 

A word of caution is warranted.  If you need to experiment to see what a dry chemical extinguisher can do, do it outside.  So many have discharged an extinguisher inside just to see it work and have paid dearly.  The powder gets into EVERYTHING!  Any nook and cranny, crevice or hole, dishes, and appliances, everything gets covered.  It is difficult to clean up because water or liquid cleaners make a paste out of it.  The serious possible side-affect is with electronic equipment because the powder is corrosive to the parts and pieces of the equipment.  It may fail in the future.  This type of extinguisher works two ways.  It removes the oxygen and it removes the heat.  Use this type on classA, B, and C fires.

Not only do extinguishers have to be the correct type, they also have to be the proper size in order to be effective.  Imagine trying to fit into size 6 shoes with size 13 feet!  It won’t work.  Imagine trying to use an undersize extinguisher.  It won’t work, but it WILL be dangerous.  Fire extinguishers also have a number rating.  For class A fires, ordinary paper and wood fires, a 1 would mean that extinguisher will do the work of 1 _ gallons of water, a 2 would mean that extinguisher will do the work of 2 _ gallons of water.  For B and C class fires, the number represents area.  For example, a 2 would indicate the extinguisher will handle a two square foot fire, a 5 would mean it will handle a five square foot fire.

We understand the science of fire, the types of extinguishers, and the classes of fires.  Now let’s cover how to use them.  Two acronyms are used to help us with this.  R.A.C.E. and P.A.S.S.

R.A.C.E. stands for Rescue, Alarm, Contain, and Extinguish.  We must first rescue ourselves and any others that may become trapped if the fire gets too big to handle.  This is especially important if there are children or handicapped people involved.   Secondly, we must notify the fire department, make the alarm.  This is the most forgotten task in almost every fire I have experienced. The person who first recognizes there is a problem waits until they havetried something, anything to put the fire out and then calls 911.  Precious minutes are lost. In fact, I think the acronym should be A.R.C.E.  You should call 911 as soon as you see a problem.  Maybe we won’t be able to handle the fire after we get there, but at least we were given the most opportunity that is available.  Thirdly, we can try to contain the fire.  This means moving the fuels that are not yet involved but are going to be soon.  This may also mean putting out the leading edge of a fire that is spreading rapidly.  And lastly, we can attempt to extinguish the fire.  This is where P.A.S.S. comes in.

P.A.S.S. simply stands for Pull, Aim, Squeeze, and Sweep.   In order for the handle to be squeezed, you need to pull the pin.   This also involves twisting the pin to break the plastic strap that holds it in place.  Next, you need to aim the extinguisher at the BASE of the fire.  This is the most effective place to put the contents of the extinguisher.  I have found in most demonstrations that people tend to aim the nozzle at the big flames above what is on fire, and all it does is fan the flames and have no effect on the fire itself. Next, you need to squeeze the handle, all the way.  And the last thing you need to do is sweep the nozzle from side to side across the base of the fire.  This will place the contents evenly and effectively over the fire.  This is another thing people forget to do.  They start to turn and run because it is getting too hot for them to stay that close.  And turning your back on a fire is never a good thing either.  Always back away whenever you are done or if the attempt has failed.  There are some conflicting thoughts on how much of theextinguisher you should use on the fire.  One idea is to start using the extinguisher and not stop until it is empty.  Another is to only use what is necessary to put the fire out.  Both ideas are fine, it just depends on the situation.  If  you are next to a doorway, use it all and ensure the fire is out.  If you are in the basement, use only what is necessary to put the fire out and save the rest as an insurance policy in case you need it on the way out.

That is fire extinguishers in a nutshell. Just how many should you have? More than you will ever need, I think.   Of course, the best way to avoid having to make all those decisions is to prevent the fire from happening.  In my next installment, I will discuss some prevention tips that you can implementin your homes.

Jim Carroll
Fire Prevention Education Officer
Grand Traverse Fire Department