Basics of portable fire extinguishers

Portable fire extinguishers are designed for small, incipient, controllable fires. The extinguishers are powered by internal pressure, and most are relatively easy to operate. Types of fires are separated into four classes, A, B, C, and D.


Portable fire extinguishers are designed for small, incipient, controllable fires. The extinguishers are powered by internal pressure, and most are relatively easy to operate.

Types of fires are separated into four classes, A, B, C, and D. Extinguishers are labeled to indicate with which type of fire they are to be used. Using the wrong extinguisher, or using it improperly, can cause spread of the fire, personal injury, or more serious consequences.

Location and accessibility of fire extinguishers are vital considerations. Extinguishers are more likely be used when they are readily available in sufficient number and type to persons familiar with their operation. Placement is best accomplished through a physical survey of the area to be protected. In general, selected locations should be visible, accessible, and uniformly distributed.

It is the responsibility of the owner or occupant of a plant to ensure the care and maintenance of extinguishers. The National Fire Protection Association standard for portable fire extinguishers (NFPA 10) requires a monthly inspection, annual maintenance, and proper recharging procedures so that a portable fire extinguisher is ready for its intended use. NFPA 10 does not require an engineer or fire inspector for the monthly inspection -- it can be done by a building owner, occupant, or a designated representative.

Annual maintenance should be conducted by either a fire extinguisher service agency representative or a trained industrial safety or maintenance person. These people should have access to the manufacturer's service manuals. General repairs or replacement of damaged components should be a part of this examination.


All personnel expected to use a fire extinguisher should be trained in its proper use.

1. Recognize the unit as the appropriate extinguisher for the type of fire. This step requires permanent marking on the unit to indicate purpose, content, and usage.

2. Transport the extinguisher to the fire. The extinguisher should be located so that it can be easily removed in a fire emergency and brought to the site of a fire as quickly as possible.

3. Basic operation involves four standard steps:

- Pull the pin

- Aim the discharge nozzle

- Squeeze the handle

- Sweep the nozzle back and forth at the fire base.


Selection of the best extinguisher for a given situation is based on a variety of factors.

- Nature of the combustibles or flammables that might be ignited.

- Potential severity (size, intensity, and speed of travel) in any resulting fire.

- Effectiveness of the fire extinguisher on that hazard.

- Ease of use.

- Availability of personnel to operate the extinguisher.

- Ambient temperature conditions and other special atmospheric considerations (wind, draft, or presence of fumes).

- Suitability of the fire extinguisher to its environment.

- Any anticipated adverse chemical reaction between the extinguishing agent and burning materials.

- Any health and operational safety concerns.

- Upkeep and maintenance requirements for the fire extinguisher.

Courtesy National Fire Protection AssociationÝ

Classes of extinguishers

Class A fires involve ordinary combustibles such as trash, paper, wood, cloth, etc. -- Put out a Class A fire by lowering its temperature using a water or water-based extinguisher or by coating the combustibles with a "multi-purpose" dry chemical. The following extinguishers are suited to Class A fires:

- Stored pressure water-filled

- Multipurpose or regular dry chemical

- Aqueous film-forming foam (AFFF)/film-forming fluoroprotein (FFFP)

- Halon*.

Class B fires involve flammable liquids, such as oil, gasoline, grease, or paint. -- Put out a Class B fire by smothering it. Use the extinguisher to give a blanketing, flame-interrupting effect. Be sure to cover the entire flaming-liquid surface. The following extinguishers are suited to Class B fires:

- Regular and multipurpose dry chemical

- Carbon dioxide

- Halon*

- Aqueous film-forming foam (AFFF)/film-forming fluoroprotein (FFFP).

Class C involves fires in electrical equipment. -- Put out a Class C fire with a nonconducting extinguishing agent to prevent electric shock. Shut off power as quickly as possible. The following extinguishers are suited to Class C fires:

- Dry chemical

- Carbon dioxide

- Halon*.

Class D fires involve combustible metals, such as chips, turnings, and shavings from magnesium, potassium alloys, etc. -- Put out a Class D fire by smothering it with dry powder compounds from a specially designed extinguisher.

* Halon production has been banned, but recycled halon can still be used to service or recharge extinguishers.

A variety of clean agent replacements are available for new extinguisher purchases; however, none of these are

suitable for existing extinguishers.

Recommended marking system

The recommended marking system combines the uses and nonuses of an extinguisher on a single label.

The pictorial presentation is easy for anyone to use and understand. Letter-shaped symbol markings

(shown above) can also be used.

Fire extinguisher types

Stored-pressure water

Stored-pressure water-filled extinguishers discharge water. Use this type when burning combustibles require a cooling and wetting action.

Stored-pressure dry chemical

Multipurpose or regular dry chemical extinguishers chemically interrupt the flaming process and coat the burning material, eliminating oxygen. This is one of the most common types of extinguishers.

Stored-pressure AFFF

Aqueous film-forming foam (AFFF) extinguishers discharge a foam concentrate solution through a special air-aspirating nozzle to produce foam. The AFFF blankets flammable or combustible liquids and prevents oxygen from fueling the fire.

Halon 1211 and halogenated agent-type stored

Halon extinguishers* chemically interrupt the flaming process. These extinguishers have traditionally been used for delicate electronic equipment fires because they leave no residue.

* Halon production has been banned, but recycled halon can still be used to service or recharge extinguishers. A variety of clean agent replacements are available for new extinguisher purchases; however, none of these are suitable for existing extinguishers.

Courtesy National Fire Protection AssociationÝ

Size, placement, and location of extinguishers

NFPA requires that the minimum number of extinguishers be installed in a location based upon the class of hazard

Class A


Light (low) Ordinary (moderate) Extra (high)

Min. rate single extinguisher 2-AÝ 2-AÝ 4-A*

Max. floor area/unit of A, sq ft 3000 1500 1000

Max. floor area for extinguisher, sq ft 11,250 11,250 11,250

Max. travel distance to extinguisher, ft 75 75 75

* Two 2 1/2 gal. water-type extinguishers can be used to fulfill the requirements of one 4-A rated extinguisher

Ý Up to two water-type extinguishers,each with a 1-A rating, can be used to fulfill the requirements of one

2-A rated extinguisher

Class B

Type Basic min. Max. travel distance

of hazard extinguisher rating to extinguishers, ft

Light (low) 5-B 30

10-B 50

Ordinary (moderate) 10-B 30

20-B 50

Extra (high) 40-B 30

80-B 50

Class C

According to NFPA, extinguishers with Class C ratings are required where energized electrical equipment can be encountered that would require a nonconducting extinguishing medium. This condition includes situations where fire either directly involves or surrounds electrical equipment. Since the fire itself would be classified as a Class A or Class B hazard, the extinguishers themselves should be sized and located on the basis of the Class A or Class B standard.

Class D

Fire extinguishers or extinguishing agents shall be located no more than 75 ft of travel distance from the Class D hazard.

Testing and inspection

Fire extinguishers must be inspected when initially placed in service and at 30-day intervals after

that time. The inspection requires a check of the following items:

- Location in designated place

- No obstruction to access or visibility

- Operating instructions on nameplate legible and facing outward

- Safety seals and tamper indicators not broken or missing

- Fullness determined by weight or "hefting"

- Examination for obvious physical damage, corrosion, leakage, or clogged nozzle

- Pressure gauge reading or indicator in the operable range or condition

- Condition of tires, wheels, carriage (for wheeled units), hose, and nozzle checked

- Hazardous materials identification systems (HMIS) label in place.

When an inspection reveals a deficiency in location, access or visibility, condition, or labeling, immediate corrective action must be taken.

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