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Fire Extinguishers

Table of Contents

  1. Introduction
  2. Basic types of fire extinguishers
  3. Extinguisher and fire classification
  4. How to choose a fire extinguisher
  5. What each type of extinguisher looks like
  6. When to use an extinguisher
  7. How to use a portable extinguisher
  8. How to fight small fires
  9. Ensuring extinguisher maintenance and code
  10. What to do after using an extinguisher
  11. Inner workings of a fire extinguisher
  12. Disclaimer



Fire is the most common serious hazard that one faces in a typical chemistry laboratory. While proper procedure and training can minimize the chances of an accidental fire, you must still be prepared to deal with a fire emergency should it occur. This document teaches you the basics about fire extinguishers -- proper types, how to use them, when and when not to use them as well as the proper procedures to follow should a fire occur. It is not a comprehensive guide; be sure to read the disclaimer given below.

If your clothing is on fire (and the floor is not), STOP, DROP and ROLL on the ground to extinguish the flames. If you are within a few feet of a safety shower or fire blanket, you can use these instead, but do not try to make it "just down the hall" if you are on fire. If one of your coworkers catches fire and runs down the hallway in panic, tackle them and extinguish their clothing.

Basic types of fire extinguishers

The two most common types of extinguishers in the chemistry laboratory are pressurized dry chemical (Type BC or ABC, left) and Carbon Dioxide (right) extinguishers:

Dry chemical picture

Dry chemical picture

CO2 extinguisher picture

CO2 extinguisher picture

In addition, you may also have a specialized Class D dry powder extinguisher for use on flammable metal fires (in a pinch, a bucket of dry sand will do, but you really should have a Class D unit if you work with flammable metals). Water-filled extinguishers are not acceptable for chemistry laboratory use. If you have a water-filled extinguisher, have it replaced immediately by contacting your campus or corporate Fire Marshal's office.

If you are not familiar with fire extinguishers and have not been trained in their use, DO NOT attempt to use them! If you work in a laboratory you should have received this training (it is usually a state or federal OSHA requirement); if not contact your supervisor immediately ( kidding).

Fire Extinguishers


Fires and extinguishers are classified according to the type of fuel that is being consumed by the fire.


  • Fires involving the combustion of ordinary materials such as wood, cloth, paper, plastics etc.
  • The extinguishers contain pressurized water or water based extinguishing agents.
  • Fires involving combustible or flammable liquids such as gasoline, kerosene and many chemical agents including gases.
  • Extinguishers contain carbon dioxide or a dry chemical extinguishing agent.
  • When extinguishing electrical fires in or around sensitive equipement such as computers, a carbon dioxide extinguisher is prefered, as it does not leave any reside that will harm subsequent operation of the equpiement
  • Fires involving energized electrical equipment such as appliances of all kinds, motors, computers etc.
  • Extinguishers contain carbon dioxide, Halon, dry chemical or liquid extinguishing agent.
  • Fires involving combustible metals such as sodium, lithium, titanium, magnesium.
  • Extinguishing agent usually comes in dry powder form stored in a bucket.
  • Fires involving cooking fats & oil in commercial cooking.
  • Extinguishing agent comes as liquid chemical.


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All extinguisher ratings are shown on the extinguisher faceplate. Each extinguisher is rated with a letter (A, B, C, D or K) corresponding to the type of fire that it can be used on (see table above).

Some extinguishers are rated to be used on more than one type of fire. These combinations are AB, AC, BC and ABC, which can be used on those types of fires corresponding to their rating letters as defined above. The combination extinguishers usually contain dry or wet chemical extinguishing agents, water, or carbon dioxide.

The ratings for A and B Class portable extinguishers are also accompanied by a numerical value which corresponds its extinguishing capacity.

Class C extinguishers do not have a numerical rating, as the fires that they are used for usually are made up of both Class A and B fires, thus requiring then to also carry an A or B rating. Class C only refers to the fact that the extinguishing medium is non-conducting and can be used on electrical fires in which the equipment is energized.

Class D extinguishers usually are specific to the metal that would potentially ignite. It only carries the letter rating to indicate the type of fire it is to be used on.

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Generally, you can tell with a glance which type an extinguisher is hanging on the wall, or in the cabinet, just by looking at its shape. Check the labels of the extinguishers in your area and note the color and shape/size of the extinguisher. This may help if someone runs in to help you fight a fire with the WRONG extinguisher (i.e. water on an electrical fire) - you can STOP them before they are injured or make matters worse!

ABC-rated multipurpose dry powder extinguishers are the most common on campus, particularly in the corridors of academic buildings. They are almost always RED in color and have either a long narrow hose or no hose (just a short nozzle). These extinguishers are very light (5-25 lbs total weight).

Water extinguishers are usually SILVER (crome-metal) in color, have a flat bottom, have a long narrow hose, are quite large (2-1/2 gallons).

CO2 (carbon dioxide) extinguishers are generally red (often yellow around aircraft or on military sites), have a LARGE "tapered" nozzle (horn), are VERY HEAVY (15-85 lbs.) These are all high-pressure cylinders.

Care should be used not to drop a CO2 cylinder; if it is damaged it can punch a hole through the nearest wall(s) and end up on the other side of campus! (The containers are quite sturdy, but don't abuse them.) CO2 cylinders do not have a pressure gauge - they must be weighed to determine the amount of contents.

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Fires have the ability to burn quickly out of control. The only time that a portable extinguisher should be used to fight a fire is when:

  • Person should be familiar with the use of a fire extinguisher.
  • The extinguisher is readily available for immediate use ( ie. is near by) and is in good working order (ie. is full of agent).
  • The extinguisher is suitable for the fire hazard being protected.
  • The fire is small enough to be controlled by the type of extinguisher present and the fire does not move from its originating position
  • The possibility that the fire will block your exit route does not exist.

If the above conditions can not be met, evacuate the area immediately.

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The easiest way to remeber how to use a portable fire extinguisher is to use the acronym PASS

P.... Pull the safety pin.

A.... Aim the extinguisher nozzle at the base of the flames.

S.... Squeeze the trigger while holding the extiguisher upright.

S.... Sweep the extinguisher from side to side, covering the area of the fire with extinguishing agent.

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Extinguish ordinary combustibles by cooling the material below its ignition temperature and soaking the fibers to prevent re-ignition. Use pressurized water, foam or multi-purpose(ABC-rated) dry chemical extinguishers.

DO NOT USE carbon dioxide or ordinary (BC-rated) dry chemical extinguishers on Class A fires.


Extinguish flammable liquids, greases or gases by removing the oxygen, preventing the vapors from reaching the ignition source or inhibiting the chemical chain reaction.

Foam, carbon dioxide, ordinary (BC-rated) dry chemical, multi-purpose dry chemical, and halon extinguishers may be used to fight Class B fires.


Extinguish energized electrical equipment by using an extinguishing agent that is not capable of conducting electrical currents.

Carbon dioxide, ordinary (BC-rated) dry chemical, multi-purpose dry chemical and halon fire extinguishers may be used to fight Class C fires. DO NOT USE water extinguishers on energized electrical equipment.

NOTE: Multipurpose (ABC-rated)chemical extinguishers leave a residue that can harm sensitive equipment, such as computers and other electronic equipment. Because of this, carbon dioxide or halon extinguishers are preferred in these instances because they leave very little residue.


Extinguish combustible metals such as magnesium, titanium, potassium and sodium with dry powder extinguishing agents specially designated for the material involved. In most cases, they absorb the heat from the material, cooling it below its ignition temperature.

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Regular maintenance and inspections of your portable fire extinguishers will provide assurance that they will operate effectively and safely if they are needed. Additional information - OSHA 1910.157(c)(4)

Inspect all extinguishers at least once a month.


  1. Is each extinguisher in its designated place, clearly visible, and not blocked by equipment, coats or other objects that could interfere with access during an emergency?
  2. Is the nameplate with operating instructions legible and facing outward?
  3. Is the pressure gauge showing that the extinguisher is fully charged (the needle should be in the green zone)?
  4. Is the pin and tamper seal intact?
  5. Is the extinguisher in good condition and showing no signs of physical damage, corrosion, or leakage?
  6. Have all dry powder extinguishers been gently rocked top to bottom to make sure the powder is not packing?  


To prevent fire extinguishers from being moved or damaged, they should be mounted on brackets or in wall cabinets with the carrying handle placed 3-1/2 to 5 feet above the floor.

Larger fire extinguishers need to be mounted at lower heights with the carrying handle about 3 feet from the floor.

The employer shall provide portable fire extinguishers and shall mount, locate and identify them so that they are readily accessible to employees without subjecting the employees to possible injury.


An Employer must:

  • Provide portable fire extinguishers for employee use and select and distribute the extinguishers based on the types of anticipated workplace fires and on the size and degree of hazard that would affect their use. 1910.157(d)(1)
  • Ensure that the travel distance for employees to any Class A extinguisher is 75 feet (22.9 meters) or less. 1910.157(d)(2)
  • Ensure that the travel distance for employees to any Class B extinguisher is 50 feet (15.2 meters) or less. 1910.157(d)(4)
  • Base the travel distance for employees to any Class C extinguisher on the pattern for the existing Class A or Class B extinguishers.1910.157(d)(5)
  • Ensure that the travel distance for employees from the combustible metal working area to any Class D extinguisher is 75 feet (22.9 meters) or less. Portable fire extinguishers for Class D hazards are required in areas where combustible metal powders, flakes, shavings, or similarly sized products are generated at least once every two weeks. 1910.157(d)(6)

If extinguishers are missing or tampered with, please report them to the Safety Officer at 397-4032 or

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After an extinguisher has been used, even just a little bit, you must report it to the Safety Officer so that it can be recharged or replaced. While CO2 and halon extinguishers will generally hold their pressure after a slight discharge, BC and ABC rated DRY CHEMICAL extinguishers will usually NOT hold a charge after partial use. While the gauge may hold steady in the green immediately after a light use, check it the next day and you'll find the gauge on EMPTY! This is because upon use the dry powder gets inside the seals and allows the nitrogen carrier gas to escape over a period of time. You can't "test" an extinguisher and put it back in the cabinet! Any discharge must be reported and the extinguisher recharged or replaced!!!






This page contains guidelines for the use of fire extinguishers and is not meant to be a comprehensive reference. There are many circumstances that these guidelines can not foresee and you should recognize the inherent danger in relying solely on this information!

If you would like to take a course on the proper use of fire extinguishers (including some hands-on training) your campus safety officer may be able to assist you. If not, try your local fire department's non-emergency phone number for more information.