While training with portable extinguishers may seem basic, it can be extremely important and should extend beyond the fire brigade. Although these extinguishers have many uses, two of the primary uses are to control fires in the incipient stage and as a tool to control specific types of fire situations.

Controlling a fire in the incipient stage, as opposed to controlling a fire that has reached the fully developed stage, can be the difference between a fire put out by one person with relatively no damage and a fire put out by numerous agencies with damages so great (including production losses) that they are difficult to calculate.

As per NFPA 10, 1.1.1 “Portable fire extinguishers are intended as a first line of defense to cope with fires of limited size.”  Another reason that this training is so pertinent is that extinguishers are generally easily accessible to all personnel not just the fire brigade.  They are carried on most emergency response vehicles, positioned throughout a facility, and are generally highly portable.  Also specific types of extinguishers to deal with specific fire situations are generally available in areas where these situations are likely to occur. 

As an explanation of why it is necessary to have such a variety of fire extinguishers I will give you a brief review of some fire science 101. At the most basic level the “fire triangle” is a good explanation of what is required for fire to occur. The triangle consisting of: oxygen, fuel (fuel can be a gas, a liquid, or a solid), and heat. For firefighting purposes, if you can remove any of the components of the triangle the fire will be extinguished.

For most of the more common fire extinguishers, the triangle will explain how they function. A more complete explanation, of the components necessary for combustion to occur, is found in the “fire tetrahedron.” The four sides of the tetrahedron consist of: oxygen (an oxidizing agent), fuel (a reducing agent), heat (temperature), and a chemical chain reaction. As in the case of the fire triangle; removing any of these components will cause combustion to cease. 

As there are four sides to the fire tetrahedron there are four general methods of fire extinguishment to go along with each side of the tetrahedron: 1.) Cooling the fire (removing heat) – this is probably the type of fire extinguishment most traditionally associated with firefighting, i.e. applying water; 2.) Excluding oxygen – this can be accomplished by numerous means such as putting a lid on a burning pan in a kitchen, or covering a burning liquid with foam; 3.) Removing fuel – this is most easily represented, in the industrial setting, as turning off a valve in order to stop the supply of a flammable substance to a fire and; 4.) Stopping the chemical chain reaction through the introduction of chemical extinguishing agents. 

Fires are generally broken down into five classifications. These classifications are mostly based on what is providing the fuel for combustion. These classifications are: A, B, C, D, and (the newer) K.

Class A consists of ordinary materials (paper, plastic, textiles, wood, cloth, etc.). Class B consists of flammable and combustible gases, liquids and greases. Class C is different in that it is not based on the fuel supporting combustion, as the fuel in a class C fire is often class A or B. Class C is a fire involving energized electrical equipment. Class D involves burning metals such as: titanium, lithium, sodium, aluminum, and magnesium. Class K (usually encountered in commercial kitchens) is combustible cooking oil and grease. 

Extinguishers are rated: A, B, C, D, or K according to what class or classes of fires they can extinguish. Extinguishers can also receive a number rating that indicates the volume of fire it can be expected to extinguish.

For class A water extinguishers this number is based on the amount of water that the extinguisher carries (each 1 = 1.25 gallons of water) so a 2- A extinguisher would carry 2.5 gallons of water. The number rating of a class B extinguisher is calculated much differently. This number is based on the square footage of burning fuel you can expect the extinguisher to extinguish.  A 20-B extinguisher should be able to extinguish 20 square feet of burning liquid. 

In the next half of this two part article I will discuss different types of fire extinguishers and extinguishing agents, different techniques to effectively utilize them and give as examples some extinguishers carried by FDNY.                                                     

James Kiesling is the Captain of Squad 1 of the Fire Department, City of New York’s Special Operations Command. He holds as AOS in fire protection technology from Corning Community College, a BA in fire and emergency services from John Jay College of Criminal Justice and an MA in homeland security and defense from the Naval Postgraduate School.