Skip Content



Tools for Your
Safety Program:
You May Also Be
Interested In:

Portable Fire Extinguishers: Maintenance, Use, Placement and Testing

Quick Tips #135


Almost all fires are small in their early stage and can be put out quickly if the proper fire extinguisher is available, and the person discovering the fire has been trained to use the fire extinguisher at hand. The requirements for portable fire extinguishers in general industry are governed by OSHA regulation 29 CFR 1910.157.

To be effective, portable fire extinguishers must be:

  1. Approved by a recognized testing laboratory (Extinguishers manufactured in the U.S. are generally approved by FM Global (FM) and listed by Underwriters' Laboratories, Inc. (UL))
  2. Of the proper type for the class of fire expected
  3. Located where they are readily accessible for immediate use and in sufficient quantity and size to deal with the expected fire
  4. Inspected and maintained on a regular basis so that they are kept in good operating condition
  5. Operated by trained personnel who can use them effectively

Classification and Use

Fire extinguishers are classified by the type of fire that they will extinguish.

Figure A


A Class A fire extinguisher is used for ordinary combustibles, such as wood, paper, some plastics and textiles. This class of fire requires the heat-absorbing effects of water or the coating effects of certain dry chemicals. Extinguishers that are suitable for Class A fires should be identified by a triangle containing the letter "A." If in color, the triangle should be green. 

Figure B


A Class B fire extinguisher is used for flammable liquid and gas fires such as oil, gasoline, etc. These fire extinguishers deprive the fire of oxygen and interrupt the fire chain by inhibiting the release of combustible vapors. Extinguishers that are suitable for Class B fires should be identified by a square containing the letter "B." If in color, the square should be red. 

Figure C


A Class C fire extinguisher is used on fires that involve live electrical equipment which require the use of electrically nonconductive extinguishing agents. (Once the electrical equipment is deenergized, extinguishers for Class A or B fires may be used.) Extinguishers that are suitable for Class C fires should be identified by a circle containing the letter "C." If in color, the circle should be blue. 

Figure D


A Class D fire extinguisher is used on combustible metals such as magnesium, titanium, sodium, etc., which require an extinguishing medium that does not react with the burning metal. Extinguishers that are suitable for Class D fires should be identified by a five- point painted star containing the letter "D." If in color, the star should be yellow. 

  A Class K fire extinguisher is used on fires involving cooking media (fats, grease and oils) in commercial cooking such as restaurants. These fire extinguishers work on the principal of saponification. Saponification takes place when alkaline mixtures such as potassium acetate, potassium citrate or potassium carbonate are applied to burning cooking oil or fat. The alkaline mixture combined with the fatty acid create a soapy foam on the surface which holds in the vapors and steam and extinguishes the fire. These extinguishers are identified by the letter K



Portable fire extinguishers are labeled so users can quickly identify the classes of fire on which the extinguisher will be effective. The marking system combines pictographs of both recommended and unacceptable extinguisher types on a single identification label. Following are examples of typical labels.

Extinguisher for Class A, B and C
Figure E Figure F Figure G
Extinguisher for Class B and C
Figure H Figure F Figure G
Extinguisher for Class A and B
Figure E Figure F Figure J
Extinguisher for Class A
Figure E Figure I Figure J


Also located on the fire extinguisher label is the UL rating. The UL rating is broken down into Class A and Class B:C ratings. These numerical ratings allow you to compare the relative extinguishing effectiveness of various fire extinguishers. For example, an extinguisher that is rated 4A:20B:C indicates the following:

  1. The A rating is a water equivalency rating. Each A is equivalent to 1.25 gallons of water. 4A=5 gal. of water.
  2. The B:C rating is equivalent to the amount of square footage that the extinguisher can cover, related to the degree of training and experience of the operator. 20 B:C=20 sq. ft. of coverage.
  3. C indicates it is suitable for use on electrically energized equipment.

When analyzing these ratings, note that there is not a numerical rating for Class C or Class D fires. Class C fires are essentially either a Class A or Class B fire involving energized electrical equipment where the fire extinguishing media must be non-conductive. The fire extinguisher for a Class C fire should be based on the amount of the Class A or Class B component. For extinguisher use on a Class D fire, the relative effectiveness is detailed on the extinguisher nameplate for the specific combustible metal fire for which it is recommended.


OSHA requires that employers select and distribute fire extinguishers based on the classes of anticipated workplace fires and also on the size and degree of the hazard, which would affect their use. The following chart contains OSHA requirements for classes of fires and travel distance to an extinguisher. NOTE: There is no distance requirement for Class K extinguishers. They are typically placed at the point of possible cooking fire ignition. Some local requirements may be more strict, so you should always check with your local fire marshal and insurance agent.


Fire Class Travel Distance

Class A* 75 ft. (22.9m) or less
Class B 50 ft. (15.2m)
Class C Based on appropriate
A or B Hazard
Class D 75 ft.


*The employer may use uniformly spaced standpipe systems or hose stations connected to a sprinkler system installed for emergency use by employees, instead of Class A portable fire extinguishers. Such systems must meet the respective requirements of 29 CFR 1910.158 or 1910.159—that they provide total coverage of the area to be protected, and that employees are trained at least annually in their use.


Where the employee has provided fire extinguishers for employee use, the employer shall provide an educational program to familiarize employees on the principles and use of the extinguishers. This educational program should be completed during the initial hiring and annually thereafter.

Maintenance, Inspection and Testing

Portable fire extinguishers must be visually inspected monthly per 1910.157 (e)(2). The inspection should assure that:

  1. Fire extinguishers are in their assigned place
  2. Fire extinguishers are not blocked or hidden
  3. Fire extinguishers are mounted in accordance with NFPA Standard No. 10 (Portable Fire Extinguisher)
  4. Pressure gauges show adequate pressure (CO2 extinguisher must be weighed to determine if leakage has occurred)
  5. Pin and seals are in place
  6. Fire extinguishers show no visual sign of damage or abuse
  7. Nozzles are free of blockage

The maintenance requirements are dependent on the type of portable fire extinguisher. Stored pressure (or dry chemical type) extinguishers do not require an internal examination. Water or steam type fire extinguishers should be discharged, disassembled and inspected annually (NFPA 10, 4-4.1.1). Dry chemical extinguishers that require a 12-year hydrostatic test are required to be emptied and subjected to applicable maintenance procedures every 6 years. Non-refillable, disposable dry chemical extinguishers are exempt from this requirement (29 CFR 1910.157(e)(4)). For additional fire extinguisher maintenance, follow the manufacturer's suggested maintenance procedure as presented in the operating manual. Hydrostatic testing of portable fire extinguishers is done to protect against unexpected in-service failure. This can be caused by internal corrosion, external corrosion, damage from abuse, etc.

Hydrostatic testing must be performed by trained personnel with proper test equipment and facilities. OSHA requires hydrostatic testing according to the following schedule:

Table 1 From 29 CFR 1910.157


Type of Extinguisher Test Interval
Soda acid (soldered brass shells) (until 1/1/82) (*)
Soda acid (stainless steel shell) 5
Cartridge operated water and/or antifreeze 5
Stored pressure water and/or antifreeze 5
Wetting agent 5
Foam (soldered brass shells) (until 1/1/82) (*)
Foam (stainless steel shell) 5
Aqueous Film Forming Foam (AFFF) 5
Loaded stream 5
Dry chemical with stainless steel 5
Carbon dioxide 5
Dry chemical, stored pressure, with mild steel, brazed brass or aluminum shells 12
Dry chemical, cartridge or cylinder operated, with mild steel shells 12
Halon 1211 12
Halon 1301 12
Dry powder, cartridge or cylinder operated with mild steel shells 12
* Extinguishers having shells constructed of copper or brass joined by soft solder or rivets shall not be hydrostatically tested and shall be removed from service by January 1, 1982. (Not permitted.)


Maintenance, inspection and testing of an extinguisher is the responsibility of the employer. Maintenance should be done at least annually or more often if conditions warrant. The employer shall record the annual maintenance date and keep these records for one year after the recorded date or the life of the shell of the extinguisher. For inspection tag options, please see fire extinguisher inspection tag.

Hydrostatic testing of portable fire extinguishers is done to protect against unexpected in-service failure. This can be caused by internal corrosion, external corrosion and damage from abuse, etc. Hydrostatic testing must be performed by trained personnel with proper test equipment and facilities. OSHA requires hydrostatic testing according to the schedule listed in 29 CFR 1910.157 Table L-1.

Fire extinguishers, correctly used on the type of fire for which they are intended, can have a large role in stopping major fire damage and dollar losses. When walking by a fire extinguisher, you'll know that all of the letters and numbers have specific meanings and why it is located where it is.

For additional information on portable fire extinguishers and their proper placement and use, contact your local fire department.


Commonly Asked Questions

Q.   Are signs required to identify fire extinguisher locations?
A.   Locations must be identified according to 29 CFR 1910.157(c)(1)
Q.   Can halon still be purchased in a portable fire extinguisher?
A.   Recycled halon can still be used in portable fire extinguishers, although it is very expensive and alternatives such as CO2 should be used when possible. Because of environmental concerns, Grainger does not carry halon fire extinguishers.



29 CFR 1910.157, Portable Fire Extinguishers.

29 CFR 1910.158, Standpipe and Hose Systems.

29 CFR 1910.159, Automatic Sprinkler Systems.

NFPA Standard #10, Portable Fire Extinguishers.

ANSI/UL 711 Rating and Testing of Fire Extinguishers.

National Fire Protection Association, Fire Protection Handbook.

National Safety Council, Accident Prevention Manual for Industrial Operations, Engineering and Technology.

American National Standards Institute (ANSI)
25 West 43rd Street, 4th floor
New York, NY 10036
(212) 642-4900

National Fire Protection Association (NFPA)
1 Batterymarch Park
P.O. Box 9101
Quincy, MA 02269
(617) 770-3000

National Safety Council
1121 Spring Lake
Itasca, IL 60143-3201

Underwriters' Laboratories (UL)
333 Pfingsten Rd.
Northbrook, IL 60062
(708) 272-8800

(Rev. 1/2014)

Find even more information you can use to help make informed decisions about the regulatory issues you face in your workplace every day. View all Quick Tips Technical Resources at

Think Safety. Think Grainger.®
Grainger has the products, services and resources to help keep employees safe and healthy while operating safer facilities. You’ll also find a network of safety resources that help you stay in compliance and protect employees from hazardous situations. Count on Grainger for lockout tagout, fall protection equipment, confined space products, safety signs, personal protective equipment (PPE), emergency response and so much more!

Please Note:
The content in this newsletter is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific compliance questions should refer to the cited regulation or consult with an attorney.

©2015 W.W. Grainger, Inc.