By:  Tony Rieck

T.R. Consulting, Inc.

May 2002 Safety Article



This month’s safety article will focus on fire extinguishers covering the following topics:


*        Basic Regulatory Overview

*        How Fires Happen

*        Types of Fires

*        Types of Extinguishers

*        Choosing Appropriate Extinguishers for the Workplace

*        Training Requirements for Employees

*        Inspection of Fire Extinguishers

*        Emergency Planning

*        Deciding to Fight or Flee

*        Basic Fire Extinguisher Use Procedures (P-A-S-S)

*        Prevention and Recognition


Note:  the information presented in this article cannot replace the need for employee training and, due to the wide variety of circumstances possible, must not be viewed as a comprehensive guide to fire safety and fire extinguisher use.  The purpose of this article is to provide basic information on the use of fire extinguishers.





Some basic requirements of OSHA regulations for portable fire extinguishers are listed below:

1. Each workplace building must have a full complement of the proper type of fire extinguisher for the fire hazards present, excepting when employer wish to have employees evacuate instead of fighting small fires.

2. Employees expected or anticipated to use fire extinguishers must be instructed on the hazards of fighting fire, how to properly operate the fire extinguishers available, and what procedures to follow in alerting others to the fire emergency.

3. Only approved fire extinguishers may be used in workplaces, and they must be kept in good operating condition. Proper maintenance and inspection of this equipment is required of each employer.

4. Where the employer wishes to evacuate employees instead of allowing employees to fight small fires, there must be written emergency plans and employee training for proper evacuation.




Fires are chemical reactions that require three elements to occur:  fuel, heat (or source of ignition) and oxygen.  Without all of these three elements, fires cannot start and, with the removal of any of these three elements, a fire will be extinguished.  Once a fire has started, the removal of the fuel source is generally not an option (with exceptions for gas leaks and similar situations).  Therefore, fire extinguishers are used to either isolate the fire from sufficient sources of oxygen or to remove the heat necessary to sustain combustion.  An explanation of the relationship of each of the three elements necessary for combustion (also referred to as the components of the fire triangle) follows:


Fuel – Fuel can be anything combustible.  Combustible materials can be solids, liquids or gases.  Combustible simply means capable of burning.  A piece of wood is combustible, a block of concrete is not.  Liquids and solids can create combustible vapor when exposed to heat and sometimes the amount of heat necessary to create the combustible vapors may be very little as in the case of gasoline where the heat necessary to form enough vapors that the vapors will burn is –45 degrees Fahrenheit. 


Oxygen – Oxygen is a primary component of the air that we breath, comprising approximately 20.9% by volume.  Fires can occur in atmospheres containing less oxygen than is necessary for human survival.  Most fires require an atmosphere containing about 16% oxygen to burn, but some materials, such as many petroleum products, can burn with as little as 11% oxygen in the atmosphere.


Heat – Heat, sometimes referred to as source of ignition, is necessary for the continuation of a fire once it has started and is the mechanism that produces the energy required to start a fire.  The amount of heat necessary to start combustion is dependant upon the fuel source.  Some flammable materials may require no more than a spark to ignite (i.e. butane) while other combustible materials require substantial heat to ignite (i.e. a large log).  Once ignited, the fire is usually capable of producing sufficient heat to continue the burning process.


Fuel, in most cases, is impossible to remove from an existing fire except through allowing all of the available fuel to be consumed by the fire over time.  Non-combustible solids (or in some cases combustible solids – i.e. a fire blanket) and inert gases can be placed between a fire and any available oxygen to “starve” the fire of oxygen and cause it to extinguish.  Ordinary combustibles such as wood and paper can have the heat taken away from them by applying water to the fire (or, as is the case with a match, by blowing the heat away from the fuel source.





A fire classification system has been devised to help us understand the different types of fires that can be encountered.  The types of fires defined under this classification system are Class A, Class B, Class C and Class D.


*        Class A fires are fires fueled by ordinary materials such as paper, lumber, cloth, plastic and cardboard.


*        Class B fires are fires fueled by flammable and combustible liquids such as fuel oils, alcohols, gasoline and acetone.


*        Class C fires are fires that involve energized electrical equipment.  It is important to note that this classification of fire may include fires involving motors or generators that are not connected to a power source.


*        Class D fires are fueled by reactive metals or pyrophoric (substances that react violently with water and/or carbon dioxide) materials.  Examples of fuels considered Class D fuels are magnesium, sodium and organomagnesium (pyrophoric).





The following extinguisher types are among the more commonly available types on the market.  The extinguishers listed below have been grouped according to the type of fire that they are effective in extinguishing.


*  Type A fires only:


1.      Water extinguishers are usually silver in color and have flat bottoms.  They are filled with pressurized water and are quite large and heavy.


2.      Foam extinguishers generally resemble water extinguishers (silver with flat bottoms), but have an inset handle in the bottom.  Foam extinguishers (other than a few new models) need to be turned upside down to start and use them.



*  Type B:C fires only:


1.      Carbon dioxide extinguishers are usually red in color with large nozzles.  These extinguishers are heavy (weighing as much as 85 pounds), pressurized cylinders without gauges.  Carbon dioxide extinguishers are weighed to determine if they are properly charged.


2.      Dry-chemical extinguishers are also generally red, but have small nozzles and gauges.  They are filled with either sodium carbonate or potassium carbonate.



*  Type A:B:C fires only:


1.      ABC dry powder extinguishers are normally red in color with small nozzles or long narrow hoses.  These extinguishers are very light and contain ammonium phosphate.


2.      Smart media extinguishers (halon and halon-alternatives) are usually red in color.  These extinguishers displace the oxygen from around the fire and “scavenge” the hydrogen radicals necessary for the combustion process to continue.  Halon is no longer produced for use in fire extinguishers due to its damaging effects on the ozone layer, but the newer halon-alternatives are now available.



*  Type D fires only:


1.      Type D fires involve materials that generate great amounts of heat and that can react violently with water and/or carbon dioxide.  This makes common extinguishing media either ineffective or counter-effective in fighting this type of fire.  Type D extinguishers are filled with materials that are quite stable (will not break down to form oxygen or carbon dioxide due to the heat generated by the fire) and work like sand to isolate the burning material from surrounding sources of oxygen.





The selection of an appropriate fire extinguisher or extinguishers has to be based upon several important criteria.  By answering the following questions, you can begin to narrow your selections.  Local fire protection companies can provide invaluable insight regarding the types, sizes (ratings), locations and the need for additional fire suppression devices (i.e. sprinklers, spray-applied fire proofing materials, fire-rated gypsum wall systems, etc.).


*        What materials are likely to be involved in a fire?  The answer to this question will tell you the type or types of fire extinguishers needed.


*        Could energized electrical equipment be involved in any fire?  If the answer to this question is yes, your extinguisher(s) will be required to include type C fire suppression.


*        How sensitive is any electrical equipment?  If there is computer or other sensitive equipment, you may want to have a fire extinguisher that contains an agent that will not leave a residue.  Many multi-purpose ABC extinguishers will leave a residue that can be difficult (or impossible) to clean from sensitive electronic equipment.  In these cases, carbon dioxide or smart media (halon alternatives) extinguishers could be good selections.


*        How large is the area (room, building, trailer, etc.) where the extinguisher will be in service?  This will dictate the size (rating) and/or number of extinguishers necessary to protect an area.  Note:  type A and type B extinguishers carry a rating number that indicates the relative ability of the extinguisher to put out a fire.  Higher rating numbers indicate a greater ability of an experienced, trained individual to fight fires of greater size.





Employees expected or anticipated to use fire extinguishers must be instructed on the hazards of fighting fire, how to properly operate the fire extinguishers available, and what procedures to follow in alerting others to the fire emergency.  Employees must be physically capable of handling the extinguisher as some extinguishers are awkward and heavy.  Written procedures, educational materials and actual experience with the type(s) of extinguisher(s) in putting out controlled fires should be a part of the training program.





The intent of monthly inspection is to provide assurance that the extinguisher will operate effectively and safely. In addition to being in its designated place (readily accessible and immediately available), and being pressurized, the extinguisher can be observed for other possible defects, such as corrosion, mechanical damage, the presence of welding, soldering, brazing, or possible tampering.


Annual, more rigorous inspections are also required except for stored pressure dry chemical fire extinguishers only.  The annual maintenance check for stored pressure dry chemical fire extinguishers can be counted as one of the monthly inspections, as long as you comply with regulatory requirements that subject the extinguishers to maintenance procedures every six years.


It is important to note that extinguishers must not be tested by squeezing the trigger to see if anything comes out.  Once the seal on the extinguisher is broken, the pressure may slowly leak out resulting in an extinguisher that has lost its charge.  Only trained individuals should conduct monthly and annual fire extinguisher inspections.




Emergency action plans are required to describe the routes to use and procedures to be followed by employees in the event of a fire.  Also, procedures for accounting for all evacuated employees must be part of the plan.  The written plan must be available for employee review.  Where needed, special procedures for helping physically impaired employees must be addressed in the plan; also, the plan must include procedures for those employees who must remain behind temporarily to shut down critical plant equipment before they evacuate.  The preferred means of alerting employees to a fire emergency must be part of the plan and an employee alarm system must be available throughout the workplace complex and must be used for emergency alerting for evacuation. The alarm system may be voice communication or sound signals such as bells, whistles or horns. Employees must know the evacuation signal.  Training of all employees in what is to be done in an emergency is required. Employers must review the plan with newly assigned employees so they know correct actions in an emergency and with all employees when the plan is changed. 

Remember that one normal response to an emergency is panic.  To reduce the likelihood of panic and to properly evaluate the procedures set forth in your emergency plan, it is important that you practice the plan (fire drill) on a regular basis.





Employees need to be instructed when to fight a fire and when not to fight.  There are four basic elements that prohibit fighting a fire under any circumstance:


*        There must be an exit behind the person fighting the fire to provide an escape route.

*        The fire must not be spreading beyond where it started.

*        The fire must not be capable of blocking your escape route.

*        There must be adequate and proper fire fighting equipment immediately available.


Other factors to be addressed prior to the decision to fight a fire include:  evacuation of employees (those not involved in fighting a fire must be notified and have begun evacuation of the affected zone or building); emergency services are notified; and, emanating smoke is not toxic and can be avoided by the operator of the extinguisher.





There is an easy to remember acronym for the proper procedures to follow when operating a portable fire extinguisher –P.A.S.S.


P          =            PULL the pin on the extinguisher

A         =            AIM the nozzle at the base of the flame

S          =            SQUEEZE the trigger while holding the extinguisher upright (most types)

S          =            SWEEP from side to side covering the entire area of the fire with extinguishing media




Employers need to implement a written fire prevention plan to complement the fire evacuation plan to minimize the frequency of evacuation. Stopping unwanted fires from occurring is the most efficient way to handle them. The written plan shall be available for employee review.

 Housekeeping procedures for storage and cleanup of flammable materials and flammable waste must be included in the plan. Recycling of flammable waste such as paper is encouraged; however, handling and packaging procedures must be included in the plan.

Procedures for controlling workplace ignition sources, such as smoking, welding and burning must be addressed in the plan. Heat producing equipment such as burners, heat exchangers, boilers, ovens, stoves, fryers, etc., must be properly maintained and kept clean of accumulations of flammable residues; flammables are not to be stored close to these pieces of equipment.

All employees are to be apprised of the potential fire hazards of their job and the procedures called for in the employer's fire prevention plan. The plan must be reviewed with all new employees when they begin their job and with all employees when the plan is changed




*        Your local fire department – they’d rather prevent than fight fires

*        The National Fire Protection Association (NFPA) writes fire safety standards and is dedicated to providing fire safety information

*        Your local fire protection service provider