There are basically four 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 so users can quickly identify the classes of fire on which the extinguisher will be effective. 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.
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 2A:10B:C indicates the following:
1. The A rating is a water equivalency rating. Each A is equivalent to 1 1/4 gallons of water. 2A = 2.5 gallons of water.
2. The B:C rating is equivalent to the amount of square footage that the extinguisher can cover, handled by a professional. 10 B:C = 10 square feet of coverage.
3. C indicates it is suitable for use on electrically energized equipment.
When analyzing these ratings, note there is not a numerical rating for Class C or Class D fires. Class C fires are essentially either a Class A or a 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.
Fire Extinguisher Ratings
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.
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.
Class C Extinguishers are suitable for use on electrical equipment 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.
Class D Extinguishers are designed for use on combustible 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.
Class K Extinguishers are used on fires involving cooking media (fats, grease, and oils) in commercial cooking sites such as restaurants. These fire extinguishers work on the principle 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 creates a soapy foam on the surface that holds in the vapors and steam and extinguishes the fire. These extinguishers are identified by the letter “K”, and are designed for use on flammable metals and are often specific for the type of metal in question.
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.
Types of Fire Extinguishers
Water extinguishers contain water and compressed gas and should only be used on Class A fires.
Foam extinguishers contain a foam that suffocates the fire and can be used for both Class A and B fires.
Dry Powder extinguishers are usually rated for multi-purpose use. They contain an extinguishing agent and use a compressed, non-flammable gas as a propellant. Should not be used on flammable metals or cooking oils.
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. These type fires often re-ignite, so you may need to continue to apply the agent even after the fire appears to be out.
Wet Chemical extinguishers can be used on wood, paper, fabric, cooking oils, and deep fat fires, but should not be used on electrical fires.
How to Use a Fire Extinguisher
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.
Stand approximately 6-8 feet away from the fire and squeeze the handle to discharge the extinguisher. If you release the handle, the discharge will stop.
Sweep the nozzle back and forth at the base of the fire and slowly move forward to extinguish the remaining fire. After the fire appears to be out, watch it carefully since it may re-ignite!
Congratulations — you did it!!!
OSHA requires that employers select and distribute fire extinguishers based on the classes of potential workplace fires and also on the size and degree of the hazard that would affect their use. The following chart contains requirements for classes of fires and travel distance to an extinguisher.
Extinguishers need to be conspicuously located and available in the case of fire. They should be located along normal paths of travel and near exits. Portable fire extinguishers should be installed on the hanger or bracket supplied or placed in cabinets or wall recesses.
The locations of fire extinguishers must be identified so they are readily available to employees without subjecting them to injury. Height requirements for mounting extinguishers depend on the weight of the unit. If the unit weighs less than 40 pounds, it should be installed so the top of the extinguisher is no more than 5 feet above the floor. If the unit weighs more than 40 pounds, it should be installed so the top of the extinguisher is no more than 3.5 feet above the floor. At
no point should the extinguisher be less 4 inches from the floor.
Federal laws state that every commercial vehicle must be equipped with a fire extinguisher. Commercial vehicles include a school bus, tractor trailer, and any truck hauling hazardous materials. Each fire extinguisher must have a gauge to indicate if the extinguisher is fully charged and must have a label showing its Underwriter’s Laboratories (UL) rating. The fire extinguisher must be attached securely and readily available and accessible for use at all times. Two fire extinguishers must have a UL rating of 4 B:C or more, or one extinguisher must have a UL rating of 10 B:C if carrying hazardous material.
Where the employer has provided fire extinguishers for employee use, the employer must 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.
Portable fire extinguishers must be visually inspected monthly. The inspection should assure that:
1. Fire extinguishers are in their assigned location;
2. Fire extinguishers are not blocked or covered;
3. Fire extinguishers are mounted in accordance with NFPA Standard No. 10 (Portable Fire Extinguishers);
4. Pressure gauges show adequate pressure;
5. Pin and seals are in place;
6. Fire extinguishers show no visual sign of damage or abuse;
7. Nozzles are free of blockage.
Maintenance, inspection, and testing of an extinguisher are the responsibility of the employer, and should be done at least annually. Regular inspection and testing of portable fire extinguishers is done to protect against unexpected service failures. This can be caused by internal or external corrosion, or damage from abuse. Hydrostatic testing must be performed by trained personnel with proper test equipment and facilities.
In summary… fire extinguishers, correctly used on the type of fire they are intended for, can have a large role in stopping major fire damage and dollar losses. However, it should be noted that it may not be possible to extinguish every fire with fire extinguishers. When personal safety is in jeopardy, personnel should not attempt to extinguish the fire, but should evacuate the building and seek safety.
In all instances, call 9-1-1 immediately if a fire occurs!