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Portable Fire Extinguishers


Workplace fires and explosions kill hundreds and injure thousands of workers each year. One way to limit the amount of damage due to such fires is to make portable fire extinguishers an important part of your fire prevention program.

When used properly, fire extinguishers can save lives and property by putting out a small fire or controlling a fire until additional help arrives.

The Fire Triangle
(Click to enlarge)

Fire and Extinguisher Operation

Fire is a very rapid chemical reaction between oxygen and a combustible material, which results in the release of heat, light, flames, and smoke.

The Fire Triangle

For a reaction that creates a fire, the following three elements, which are represented by the three sides of the Fire Triangle, must be present at the same time:

  1. Enough oxygen to sustain combustion,
  2. Enough heat to raise the material to its ignition temperature, and
  3. firetetrahedron
    The Fire Tetragedron
    (Click to enlarge)
  4. Some sort of fuel or combustible material.

The Fire Tetrahedron

The Fire Tetrahedron introduces a fourth component – the uninhibited chain reaction – to the fire triangle. This representation more accurately describes the fire as a chain reaction process. The chain reaction acts as a feedback loop mechanism of heat to produce the gaseous fuel used in the flame. This feedback provides the heat necessary to maintain the fire. The fuel, oxygen and heat join together in a sustained chemical reaction.

Check out this short video on the the elements of fire and explosion.


Fire Extinguisher Usage

Portable fire extinguishers apply an extinguishing agent that will either cool burning fuel, displace or remove oxygen, or stop the chemical reaction so a fire cannot continue to burn. When the handle of an extinguisher is compressed, agent is expelled out the nozzle. A fire extinguisher works much like a can of hair spray.

All portable fire extinguishers must be approved by a nationally recognized testing laboratory to verify compliance with applicable standards. Equipment that passes the laboratory's tests are labeled and given an alpha-numeric classification based on the type and size of fire it will extinguish.

Check out this short audio clip by Dan Clark of the Fire extinguisher operation is not as easy as point-and-shoot. We explain the types of fires, and the types of extinguishers, and how to use them. What’s burning? Is the source wood, gasoline or electrical? What’s inside the fire extinguisher makes a difference. In this podcast, Dan describes the types of fires, and the various types of fire extinguishers to use on them.

Fire Extinguisher Ratings

There are basically five different types or classes of fire extinguishers, each of which extinguishes specific types of fire. Newer fire extinguishers use a picture/labeling system to designate which types of fires they are to be used on. Older fire extinguishers are labeled with colored geometrical shapes with letter designations. Both of these types of labels are shown below with the description of the different classes of extinguishers.

Additionally, Class A and Class B fire extinguishers have a numerical rating which is based on tests conducted by Underwriter´s Laboratories that are designed to determine the extinguishing potential for each size and type of extinguisher.

A-2 Class A Extinguishers will put out fires in ordinary combustibles, such as wood and paper. The numerical rating for this class of fire extinguisher refers to the amount of water the fire extinguisher holds and the amount of fire it will extinguish. A-1

B-2 Class B Extinguishers should be used on fires involving flammable liquids, such as grease, gasoline, oil, etc. The numerical rating for this class of fire extinguisher states the approximate number of square feet of a flammable liquid fire that a non-expert person can expect to extinguish. B-1

C-2 Class C Extinguishers are suitable for use on electrically energized fires. This class of fire extinguishers does not have a numerical rating. The presence of the letter "C" indicates that the extinguishing agent is non-conductive. C-1

Class D Extinguishers are designed for use on flammable metals and are often specific for the type of metal in question. There is no picture designator for Class D extinguishers. These extinguishers generally have no rating nor are they given a multi-purpose rating for use on other types of fires. d-1

Class K Extinguishers, or Wet Chemical, fire extinguishers are designed specifically for use in restaurant kitchens. They utilize a potassium acetate based, low PH agent - the same agent used in pre-engineered cooking equipment fire extinguishing systems. The agent discharges as a fine mist which helps prevent grease splash and fire re-flash while cooling the appliance. The Class K extinguisher is the ideal choice for use on all cooking appliances including solid fuel charbroilers. d-1

Multi-Class Ratings

Many extinguishers available today can be used on different types of fires and will be labeled with more than one designator, e.g. A-B, B-C, or A-B-C. Make sure that if you have a multi-purpose extinguisher it is properly labeled.


This is the old style of labeling indicating suitability for use on Class A, B, and C fires.

This is the new style of labeling that shows this extinguisher may be used on Ordinary Combustibles, Flammable Liquids, or Electrical Equipment fires. This is the new labeling style with a diagonal red line drawn through the picture to indicate what type of fire this extinguisher is NOT suitable for.


In this example, the fire extinguisher could be used on Ordinary Combustibles and Flammable Liquids fires, but not for Electrical Equipment fires.

Halon Fire Extinguisher
(Click to enlarge)

Types of Fire Extinguishers

Different types of fire extinguishers are designed to fight different types of fire. The three most common types of fire extinguishers are: air pressurized water, CO2 (carbon dioxide), and dry chemical. The copy below provides information regarding the type of fire and which fire extinguisher should be used.

Dry Chemical extinguishers are usually rated for multiple purpose use. They contain an extinguishing agent and use a compressed, non-flammable gas as a propellant.

Halon extinguishers contain a gas that interrupts the chemical reaction that takes place when fuels burn. These types of extinguishers are often used to protect valuable electrical equipment since they leave no residue to clean up. Halon extinguishers have a limited range, usually 4 to 6 feet. The initial application of Halon should be made at the base of the fire, even after the flames have been extinguished.

Water These extinguishers contain water and compressed gas and should only be used on Class A (ordinary combustibles) fires.

Carbon Dioxide (CO2) extinguishers are most effective on Class B and C (liquids and electrical) fires. Since the gas disperses quickly, these extinguishers are only effective from 3 to 8 feet. The carbon dioxide is stored as a compressed liquid in the extinguisher; as it expands, it cools the surrounding air. The cooling will often cause ice to form around the horn where the gas is expelled from the extinguisher. Since the fire could re-ignite, continue to apply the agent even after the fire appears to be out.

More on Extinguisher Labeling


Look at the extinguisher to the right. The classification is:


The letters (A, B, and C) represent the type(s) of fire for which the extinguisher has been approved.

The number in front of the A rating indicates how much water the extinguisher is equal to and represents 1.25 gallons of water for every unit of one. For example, a 4-A rated extinguisher would be equal to five (4 x 1.25) gallons of water.

The number in front of the B rating represents the area in square feet of a class B fire that a non-expert user should be able to extinguish. Using the above example, a non-expert user should be able to put out a flammable liquid fire that is as large as 10 square feet.

Please click here for more information on each type of fire extinguisher.

How to Use a Fire Extinguisher

Even though extinguishers come in a number of shapes and sizes, they all operate in a similar manner.  Here's an easy acronym for fire extinguisher use:

P  A  S  S -- Pull, Aim, Squeeze, Sweep

Pull the pin at the top of the extinguisher that keeps the handle from being accidentally pressed.

Aim the nozzle toward the base of the fire.

Squeeze the handle to discharge the extinguisher. Position yourself approximately 8 feet away from the fire. If you release the handle, the discharge will stop.

Sweep the nozzle back and forth at the base of the fire. After the fire appears to be out, watch it carefully since it may re-ignite!

Make sure all employees who are expected to use fire extinguishers if a controllable fire occurs are properly training with hands-on practice. There's no OSHA requirement to actually extinguish a fire or discharge a fire extinguisher during training. However, each employee should handle the fire extinguisher and demonstrate they can perform the PASS steps.

Please click on the video below to learn more about the PASS technique:


Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. Each of the following is a component of the Fire Triangle, except _____.

2. Which of the following is NOT a purpose of the Portable fire extinguisher?

3. Class ___ Extinguishers should be used on fires involving flammable liquids, such as grease, gasoline, oil, etc.

4. Class ___ Extinguishers are designed for use on flammable metals and are often specific for the type of metal in question.

5. Class ___ Extinguishers will put out fires in ordinary combustibles, such as wood and paper.

6. Class ___ Extinguishers are suitable for use on electrically energized fires.

7. Class K portable fire extinguishers are designed specifically for use in which of the following locations?

8. These extinguishers contain water and compressed gas and should only be used on Class A (ordinary combustibles).

9. These extinguishers are usually rated for multiple purpose use.

10. The acronym "PASS" stands for _____.

Have a great day!

Important! You will receive an "error" message unless all questions are answered.