In the next several endeavors, I will try to return to the foundations where we all started: Basic Fire 101. Some of you use the National Fire Academy “Coffee Break Training” or some version of “kitchen table” training with the morning cup(s) of coffee, afternoon “breaks” or at the station for weekly/biweekly/monthly training. This will be an attempt to break the monotony of “Hey, Cap – what’s for training?” I guess this can be considered the quarterly memory jog. Some of the topics will be “new” as some firefighters have not dwelled on them since Firefighter I and II or Rookie School. The adage of “if you don’t use it – you’ll lose it” is very appropriate, as I have learned for myself.
Trends have led themselves to cycle around, be repackaged and redelivered or created anew. This quarter’s topic is a forgone and sometimes forgotten subject – portable fire extinguishers. There they sit, usually in brackets, waiting to be used. They are of different types, shapes and forms; all are under some kind of pressure at any time. In order for them to be used correctly, we, the operator, must understand certain items: fire behavior, some chemistry, a little physics and use of the tool itself. Sound tough?
First things first. Keep in mind that an extinguisher is designed for small fires; the big colored (usually red) vehicle that arrives on the scene with you is for the bigger fires. This is one of the few subjects that we, as fire and life safety professionals, actively teach to the public. If we don’t understand the tool we are to be knowledgeable about as part of our job, how can we — as the same “professionals” — be expected to teach others, public or ourselves?
Classes of fire these
Those of us having been in this business for a while remember the basic four — Classes A through D. These traditional classes are listed in order:
Ordinary Combustibles (wood, paper, trash, grass, plastics)
Flammable and Combustible Liquids (gasoline, diesel fuel, heating oil, kerosene, some cooking oils)
Energized electrical components (the electrical component must be energized to be Class C; if not – then this fire is considered Class A, B or D)
Combustible metals (magnesium, titanium, sodium, etc.)
About 10 years ago, the National Fire Protection Association (NFPA) developed a new class. Class K includes combustible cooking oils and animal fats — due to the fact that cooking oils were becoming a problem for dry chemical extinguishers to put out. The dry chemical agent would put out the surface fire, but reignition is highly possible because the oil itself is still hot, vaporizing and looking for another ignition source. This is similar in nature to LP gas fires. Put out the flame without turning off the gas at the same time equals reignition upon finding another ignition source, which equals worse than the original situation.
The stuff inside those shells is called agent. Agents work by eliminating certain parts of the fire tetrahedron, some work on multiple sides. Agents come from all three states of matter — solid, liquid or gas. Some of the most popular agents used are water. The water can be with a foam concentrate additive or plain, dry powder (Class D agents — Met-L-X, Lith-X, Na-X, etc.), carbon dioxide (compressed gas) and dry chemical – sodium or potassium-based or multipurpose ammonium phosphate. There are some newer agents for certain kinds of applications that are either a gas or liquid. Halon replacements (FM-200 and DuPont FE-36) for Halon 1211 extinguisher applications near sensitive areas and wet (water mixed with potassium-based) agents with a low pH to not only control the surface vapor fire of cooking oils and/or animal fats, but cool cooking oil as well.
Rating systems of extinguishers are important. What the extinguisher can do and the classes of fire it can put out have an impact on other tactical decisions to be made. Testing is done by the manufacturer and either Underwriters Laboratories or Factory Mutual Test labs to determine how much fire an extinguisher can be expected to put out. Only Class A and B have numeric ratings (1-A to 40-A, 1-B to 640-B). These numbers relate to how much fire an untrained bystander can be expected to put out — Class A in cubic feet, Class B in square feet, because of the particular tests used. Class C is only tested for electrical conductivity of the agent; if no electrical shock is transmitted through the agent stream, then a Class C rating is received. Class D is not rated, but is fuel-specific. This means the agent must match the metal fuel involved. Potassium-based dry powder agent does not work well with sodium-based metal fire without a significant chemical reaction happening. Class K is rated for its own class and does carry a Class A rating if needed.
Application of agent to fire now comes into play. We’ve seen the fire, know what is burning and have chosen our extinguisher and agent to suppress the fire. The term PASS is an acronym for how to use the extinguisher:
P — Pull the safety pin by using a twist/pull method to break the safety tab holding the pin in place
A — Aim the nozzle of the extinguisher at the base of the fire
S — Squeeze the handle together to release the agent from the shell
S — Sweep the base of the fire. This interrupts the chemical chain reaction of the fire tetrahedron and will stop the combustion process in various ways — cooling surfaces, separating atmospheric oxygen from the process, smothering, etc.
Although on a smaller scale, this is similar to using fire streams — both still attack the base of the fire. An exception to this is Class D combustible metal fires. Dry powder agents have to be applied in layers as these fires can forcibly create reactions that make situations worse. Try applying water or dry chemical to a magnesium shaving pile burning — talk about fireworks and exposure issues close to the area!
Maintenance of extinguishers is important. Monthly checks of the units hanging in the stations and on apparatus need to be completed. Extinguishers mounted on apparatus are exposed to more vibration and shock from the chassis that leads to possible packing of the dry chemical and dry powder agents. Loosening dry chemical and powder agents by shaking or tapping the shell with a rubber mallet allows the unit to stay operational. Checking gauges on dry chemical, dry powder and pressurized water extinguishers allows operator to see if unit has leaked any stored pressure within the shell. Carbon dioxide extinguishers are weighed to check for fullness as these shells are under high pressure and have no gauge.
Just like air cylinders of SCBA, these shells are on a testing schedule as well. Stainless steel cylinders are on five year hydrostatic testing schedules, aluminum and mild steel shells are on 12 year rotations, carbon dioxide shells follow five year intervals per Federal DOT. Maintaining records on extinguishers are important. You must have that paper trail — computer file — to make sure what we use is safe for us and well maintained. A firefighter carrying a 10 pound grenade when the shell fails is not a fun day.
These are some facts that can fill a training session. NFPA 10 Portable Fire Extinguishers has more information on what extinguishers are used in which occupancy, travel distances in hazard areas and so on. Continue to review and study on all parts of our “foundations” so cracks in the structure will not force “demolition.” “Remodeling” is okay. Besides, who wants to look at the same wallpaper or paint for 30 years?
Stay safe in the streets and “make every day a training day!”