This is the second column in a two-part series about portable fire extinguishers. In the first column, I covered some basic fire science as it pertains to fire extinguishment; particularly the fire triangle and the fire tetrahedron. This was then related to the necessity of having a variety of fire extinguishers in order to deal with various fire situations.
In this column, I will address specific types of fire extinguishers and extinguishing agents, touch on various methods of applying extinguishing agents, and I will also put forth as examples some of the fire extinguishers carried by FDNY.
Portable fire extinguishers can range in size from small units that can be operated with one hand or worn on the back, all the way to large wheeled units. However, more important than the fire extinguisher’s size is its extinguishing agent (the method of extinguishment). I say more important because a fire extinguisher of inadequate size may fail to extinguish a fire, but one utilizing an incompatible extinguishing agent can make matters significantly worse.
Different types of agents will work better on different types of fires. Choosing the incorrect fire extinguisher can be ineffective in extinguishing the fire. It can also have consequences ranging from destroying electronics to something much more catastrophic.
To illustrate some of this catastrophic potential, the 2019 edition of NFPA 484 (Standard for Combustible Metals) offers numerous warnings as to the hazards of utilizing inappropriate agents to extinguish a combustible metal fire. Several examples are:
- Water in contact with molten combustible metals will result in violent steam explosions and can cause hydrogen explosions and reactions
- Water when applied to most burning combustible metals results in an increase in burning intensity and possible explosion
- Application of carbon dioxide on combustible-metal fire adds to the intensity of the burning. Most combustible metals ignite and burn in 100 percent carbon dioxide atmospheres.
- Dry chemical extinguishers react with alkali metals and intensify the fire.
- Halogenated extinguishing agents used on alkali metals can result in an explosion.
The extreme difficulty involved is attempting to extinguish certain types of fires as well as the dangers inherent in choosing an inappropriate extinguishing agent have long been recognized by the fire service. When researching for this article I was reading an old edition of “The Fire Chief’s Handbook.”
The authors were in agreement as to the danger of choosing an unsuitable means of extinguishment. In it they discussed the hazards of various types of combustible metal fires. When referring to one particular type of metal fire they state that “Not all authorities are in agreement on the possibility of extinguishing” this type of fire. “Some state that it is not possible to do so. Others call attentions to the ineffectiveness of certain types of extinguishing agents. One thing is agreed upon: Water should not be used.”
- Portable fire extinguishers can deliver numerous types of extinguishing agents to address various fire conditions, such as:
- Water – Used for Class A fires.
- Dry Chemical – Works well on Class B and C fires (some work on Class A fires as well).
- Carbon Dioxide (CO2) – Employed on Class B and C fires. CO2 is particularly effective for use on delicate electronics, but not effective on pressurized fuel or grease fires.
- Foam – Can be used on Class A and B fires depending upon the type of foam.
- Wet Chemical – Specifically made for use on Class K fires.
- Halogenated Agents (also known as clean agents) – Since these don’t leave a residue and are non-conductive, they are effective for use on delicate electronics.
- Dry Powder – These are used on Class D fires. Different dry powders are used for specific types of metal fires.
The techniques of applying the various extinguishing agents are too numerous to be covered here in any depth. The examples that follow are specifically from the FDNY Training Bulletin, Purple K Dry Chemical Extinguisher (September 1, 2010). To fully illustrate one of the techniques as an example I will elaborate on a procedure to extinguish liquefied petroleum gas (LPG) fires (incorporating water), as laid out in this bulletin.
Application techniques with this extinguisher include techniques for:
- Flammable liquid spill fires
- Flammable liquid spill fires with an obstacle
- Flammable liquid fires in depth
- Flammable liquid fires in depth with an obstacle
- Gravity fed fires
- Three dimensional gravity fed fires
- Flammable liquid pressure fires
- Flammable gas pressure fires
- Liquefied petroleum gas (LPG) fires (incorporating water)
Extinguishing LPG fires (incorporating water):
Utilizing water and dry chemical extinguishing agents in conjunction can be highly effective in extinguishing LPG fires. The water acts as a coolant and heat shield, protecting the members, while the dry chemical acts to extinguish the fire.
The firefighters approach the fire from an upwind position while operating the hose lines in a fog pattern for protection. (fig. 1)
When in range the firefighter with the dry chemical extinguisher directs the stream at the fuel source (broken flange). (fig. 2)
In the event a spill fire is present, direct the stream of dry chemical down the stream of escaping fuel to the ground spill and with a side-to-side sweeping motion extinguish the spill fire. (fig. 3)
Upon extinguishing the fire continue to cool the piping and surrounding area with the hose lines. Next close the supply valve to stop the fuel flow. While this is occurring the firefighter with the dry chemical extinguisher should stand by in case of a re-ignition. (fig. 4)
CAUTION: These fires should not be extinguished unless the immediate shutoff of the fuel source is possible.
FDNY carries several types of portable fire extinguishers to address a wide variety of situations. In some cases local fire companies are familiarized with other specific extinguishing agents by pre-planning with industrial facilities within their response areas.
Some of the fire extinguishers carried by the FDNY include:
- The 2 ½ gallon pressurized water extinguisher
- The aqueous film forming foam (AFFF) extinguisher
- Various dry chemical extinguishers
- The “Indian Pump” – This is a five-gallon backpack fire pump that is mainly utilized by FDNY at brush fires.
- The MET-L-X handheld extinguisher – These are used on Class D (combustible metal) fires. It was developed for use on certain alkali metals, including sodium and potassium, but can also be used on magnesium, titanium, and zirconium.
- The LITH-X handheld extinguisher - may be used on Class D fires. They can be used on certain alkali metals including lithium, sodium, and potassium. The LITH -X extinguisher was specifically developed for use on lithium fires (batteries), but is also effective to extinguish magnesium. LITH-X is also capable of containing and, in some cases, completely extinguishing, fires involving zirconium, titanium, and sodium-potassium alloys.
- Purple K dry chemical extinguisher - Purple K is a potassium bicarbonate base dry chemical. Purple K is a superior extinguishing agent on methanol fires and is also effective on gasoline, diesel and compressed gas fires.
FDNY places such a high emphasis on the portable fire extinguisher as a firefighting tool that one of its designated positions is named after it. A six-member truck company has one member assigned to the extinguisher position, generally referred to as “the can” or the “can man.” The can is in reference to the 2½ gallons pressurized water extinguisher that this member carries as a normal part of their equipment. As one of their tool choices this member has the option to carry the same type of extinguisher filled with a water/foam mixture, the foam being aqueous film forming foam (AFFF); depending on the situation at hand.
Some other uses of the basic pressurized water extinguisher are to: temporarily protect members while they gain control of a door to isolate a fire; to cool a burn victim; to cool metal while cutting (with a torch or saw) someone free during a man-in-machine rescue or impalement; and to flush someone clean that was exposed to certain hazardous materials.
With the appropriate training not just members of the fire brigade, but other personnel working at a facility can have a tremendous impact on a potential fire situation by containing the fire or, better yet, extinguishing it in the incipient stage. In addition this training can ensure that personnel do not exacerbate the situation by utilizing an inappropriate portable fire extinguisher.
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.
Editor's note: As with choosing the appropriate agent to extinguish a fire you must be certain that water will not make the hazardous material exposure worse.