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The Fire Triangle
Fire Safety, at its most basic, is based upon the
principle of keeping fuel sources and ignition
sources separate.

The Fire Triangle
1. Enough OXYGEN to sustain combustion
2. Enough HEAT to reach ignition temperature
3. Some FUEL or combustible material
Together, they produce the CHEMICAL
REACTION that is fire
Three things must be present at the same time to
produce fire:
Take away any of these things and
the fire will be extinguished

Fuel Classifications
• Fires are classified according to the type of
fuel that is burning.
• If you use the wrong type of fire extinguisher
on the wrong class of fire, you might make
matters worse.
• Its very important to understand the four
different fire (fuel) classifications…

Class A: Wood, paper, cloth, trash, plastics—
solids that are not metals.
Class B: Flammable liquids—gasoline, oil,
grease, acetone. Includes flammable gases.
Class C: Electrical—energized electrical
equipment. As long as it’s “plugged in.”
Class D: Metals—potassium, sodium, aluminum,
magnesium. Requires Metal-X, foam, and other
special extinguishing agents.

Most fire extinguishers will have a pictograph label
telling you which types of fire the extinguisher is
designed to fight.
For example, a simple water extinguisher might have
a label like this…
…which means it should only be used on Class A fires.

Types of Fire Extinguishers
Different types of fire extinguishers are designed to
fight different classes of fire.
The 3 most common types of fire extinguishers are:
1. Water (APW)
2. Carbon Dioxide (CO2)
3. Dry Chemical (ABC, BC, DC)

1. Water (APW) Fire Extinguishers
Large silver fire
extinguishers that stand
about 2 feet tall and
weigh about 25 pounds
when full.
APW stands for “Air-
Pressurized Water.”
Filled with ordinary tap
water and pressurized
air, they are essentially
large squirt guns.

APW’s
extinguish fire
by taking away
the “heat”
element of the
Fire Triangle.

APW’s are designed for Class A fires only:
Wood, paper, cloth.
Using water on a flammable liquid fire could cause
the fire to spread.
Using water on an electrical fire increases the risk of
electrocution. If you have no choice but to use an
APW on an electrical fire, make sure the electrical
equipment is un-plugged or de-energized.

APWs will be found in older buildings, particularly in public
hallways, as well as in Residence Halls.
They will also be found in computer
laboratories. It is important to remember,
however, that computer equipment must be
disconnected from its electrical source before
using a water extinguisher on it.

2. Carbon Dioxide Fire Extinguishers
CO2 cylinders are red. They range in size from 5 lbs to 100 lbs or
larger. On larger sizes, the horn will be at the end of a long,
flexible hose.
The pressure in
a CO2
extinguisher is
so great, bits of
dry ice may
shoot out of the
horn!

CO2s will frequently be found in laboratories, mechanical
rooms, kitchens, and flammable liquid storage areas.
CO2’s are designed for Class B and C
(Flammable Liquids and Electrical Sources)
fires only!
In accordance with NFPA regulations (and manufacturers’
recommendations), all CO2 extinguishers at OSU undergo
hydrostatic testing and recharge every 5 years.

CO2 is very cold as it comes out of the extinguisher, so it
cools the fuel as well.
Carbon dioxide is a
non-flammable gas
that takes away the
oxygen element of
the fire triangle.
Without oxygen,
there is no fire.

Class A materials may also smolder and
re-ignite.
A CO2 may be ineffective in
extinguishing a Class A fire because it
may not be able to displace enough
oxygen to successfully put the fire
out.

3. Dry Chemical (ABC) Fire Extinguishers
The powder also works to interrupt the chemical reaction of
fire. These extinguishers are very effective at putting out
fire.
Dry chemical
extinguishers put
out fire by
coating the fuel
with a thin layer
of dust. This
separates the fuel
from the oxygen
in the air.

At OSU, “ABC” fire extinguishers are filled with a fine
yellow powder. The greatest portion of this powder is
composed of monoammonium phosphate. The extinguishers
are pressurized with nitrogen.
ABC extinguishers are
red. On campus, they
range in size from 5
to 20 lbs.

You may see them labeled:
• DC (for “Dry Chemical”)
• ABC (can be used on Class A, B, or C fires)
• BC (designed for use on Class B and C fires)
Dry chemical
extinguishers come in
a variety of types…

An “ABC” extinguisher will have a label
like this, indicating it may be used on
Class A, B and C fires.
It is extremely important to identify which types of dry
chemical extinguishers are located in your area!
You don’t want to mistakenly use a “BC” extinguisher on a
Class A fire thinking that it was an “ABC” extinguisher.

Dry chemical extinguishers with
powder designed for Class B and C fires
(“BC” extinguishers) may be located in
places such as commercial kitchens and
areas with flammable liquids.
On campus, you will find ABC’s in public hallways of new
buildings, in laboratories, break rooms, offices, chemical
storage areas, mechanical rooms, University vehicles, etc.

How to Use a Fire Extinguisher
It’s easy to remember how to use a fire
extinguisher if you remember the acronym
PASS:
 Pull
 Aim
 Squeeze
 Sweep

Pull the pin…
This will allow
you to
discharge the
extinguisher

Aim at the base of the fire…
Hit the fuel.
If you aim at
the flames...
… the extinguishing agent will fly right
through and do no good.

Squeeze the top handle…
This depresses a
button that
releases the
pressurized
extinguishing
agent.

Sweep from side to side…
.. until the fire is
completely out.
Start using the extinguisher
from a safe distance away,
then slowly move forward.
Once the fire is out, keep an eye on the area in case
it re-ignites.

Rules for Fighting Fires
Fires can be very dangerous and you should always be certain
that you will not endanger yourself or others when attempting
to put out a fire.
For this reason, when a fire is discovered…
1. Assist any person in immediate danger to safety, if it
can be accomplished without risk to yourself.
2. Call 911 or activate the building fire alarm. The fire
alarm will notify the fire department and other building
occupants and shut off the air handling system to
prevent the spread of smoke.
If the fire is small (and Only after having done these
2 things), you may attempt to use an extinguisher to
put it out. However . . . .

. . . before deciding to fight the fire, keep these
things in mind:
1. Know what is burning. If you don’t know what’s
burning, you won’t know what kind of extinguisher to
use.
2. Even if you have an ABC fire extinguisher, there may be
something in the fire that is going to explode or
produce toxic fumes.
Chances are you will know what’s burning, or at
least have a pretty good idea, but if you don’t, let
the fire department handle it.

. . . before deciding to fight the fire, keep these
things in mind:
3. Is the fire spreading rapidly beyond the point where it
started? The time to use an extinguisher is at the
beginning stages of the fire.
4. If the fire is already spreading quickly, it is best to
simply evacuate the building.
As you evacuate a building, close doors and windows
behind you as you leave. This will help to slow the
spread of smoke and fire.

Do not fight the fire if:
 You don’t have adequate or appropriate equipment.
If you don’t have the correct type or large enough
extinguisher, it is best not to try fighting the fire.
 You might inhale toxic smoke. When synthetic
materials such as the nylon in carpeting or foam
padding in a sofa burn, they can produce hydrogen
cyanide, acrolein, and ammonia in addition to carbon
monoxide. These gases can be fatal in very small
amounts.
 Your instincts tell you not to. If you are
uncomfortable with the situation for any reason, just
let the fire department do their job.

The final rule is to always position yourself with an exit
or means of escape at your back before you attempt to
use an extinguisher to put out a fire.
In case the extinguisher malfunctions, or something
unexpected happens, you need to be able to get out
quickly. You don’t want to become trapped.

I. WHAT ARE THE 3 ELEMENTS NEEDED
FOR FIRE TO IGNITE? AND HOW DO
THEY PRODUCE FIRE?
II. THREE MOST COMMON TYPE OF FIRE
EXTINGUISHER.
III. WHAT DOES PASS STANDS FOR?
IV. BEFORE DECIDING TO FIGHT THE FIRE,
WHAT SHOULD BE KEPT IN MIND FIRST?

V. WHAT WILL HELP YOU SLOW THE
SPREAD OF SMOKE

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