Fire Extinguisher Safety:

Basic types of fire extinguishers

The two most common types of extinguishers in the chemistry laboratory are pressurized dry chemical (Type BC or ABC, ) and carbon dioxide.
In addition, you may also have a specialized Class D dry powder extinguisher for use on flammable metal fires.
Water-filled extinguishers are not acceptable for chemistry laboratory use. If you have a water-filled extinguisher, have it replaced immediately by contacting the campus safety officer.

Classification of Fires

Class A fires are ordinary materials like burning paper, lumber, cardboard, plastics etc.
Class B fires involve flammable or combustible liquids such as gasoline, kerosene, and common organic solvents used in the laboratory.
Class C fires involve energized electrical equipment, such as appliances, switches, panel boxes, power tools, hotplates and stirrers. Water is usually a dangerous extinguishing medium for class C fires because of the risk of electrical shock unless a specialized water mist extinguisher is used.
Class D fires involve combustible metals, such as magnesium, titanium,potassium and sodium as well as pyrophoric organo-metallic reagents such as alkyllithiums, Grignards and diethylzinc. These materials burn at high temperatures and will react violently with water, air, and/or other chemicals. Handle with care!!
Class K fires are kitchen fires. This class was added to the NFPA portable extinguishers Standard 10 in 1998. Kitchen extinguishers installed before June 30, 1998 are "grandfathered" into the standard.

Fire extinguisher ratings

Some fires may be a combination of these! Your fire extinguishers should have ABC ratings on them. These ratings are determined under ANSI/UL Standard 711 and look something like "3-A:40-B:C". Higher numbers mean more firefighting power. In this example, the extinguisher has a good firefighting capacity for Class A, B and C fires.

Typical extinguishers and their uses:

Water extinguishers (not found in laboratories) are suitable for class A (paper, wood etc.) fires, but not for class B, C and D fires such as burning liquids, electrical fires or reactive metal fires. In these cases, the flames will be spread or the hazard made greater!
Water mist extinguishers are suitable for class A and C;
Dry chemical extinguishers are useful for class ABC fires and are your best all around choice. They have an advantage over CO2 extinguishers in that they leave a blanket of non-flammable material on the extinguished material which reduces the likelihood of reignition. They also make a terrible mess -- but if the choice is a fire or a mess, take the mess! Note that there are two kinds of dry chemical extinguishers!
Type BC fire extinguishers contain sodium or potassium bicarbonate.
Type ABC fire extinguishers contain ammonium phosphate.
CO2 (carbon dioxide) extinguishers are for class B and C fires. They don't work very well on class A fires because the material usually reignites.
CO2 extinguishers have an advantage over dry chemical in that they leave behind no harmful residue.
That makes carbon dioxide or Halotron I; a good choice for an electrical fire involving a computer or other delicate instrument. Note that CO2 is a bad choice for a flammable metal fires such as Grignard reagents, alkyllithiums and sodium metal because CO2 reacts with these materials.
Metal/Sand Extinguishers are for flammable metals (class D fires) and work by simply smothering the fire with powdered copper metal or sodium chloride (NaCl).
You should have an approved class D unit if you are working with flammable metals.
The copper extinguishing agent is preferred for fires involving lithium and lithium alloys. It is the only known lithium fire fighting agent which will cling to a vertical surface thus making it the preferred agent on three dimensional and flowing fires.
Sodium chloride works well for metal fires involving magnesium, sodium (spills and in depth), potassium, sodium potassium alloys, uranium and powdered aluminum. Heat from the fire causes the agent to cake and form a crust that excludes air and dissipates heat.

Some other less-common extinguishers that are worth noting.

Halotron I extinguishers, style like carbon dioxide units, are for use on class B and C fires.
Halotron I is an ozone-friendly replacement for Halon 1211 (which was banned by international agreements starting in 1994). This "clean agent" discharges as a liquid, has high visibility during dischage, does not cause thermal or static shock, leaves no residue and is non-conducting. These properties make it ideal for computer rooms, clean rooms, telecommunications equipment, and electronics. The superior properties of Halotron come at a higher cost relative to carbon dioxide.
FE-36TM (Hydrofluorocarbon-236fa or HFC-236fa) is a DuPont-manufactured Halon 1211 replacement that is available commercially in Cleanguard® extinguishers. The FE-36 agent is less toxic than both Halon 1211 and Halotron I. In addition, FE-36 has zero ozone-depleting potential; FE-36 is not scheduled for phase-out wheras Halotron I production is slated to cease in 2015.
Water mist extinguishers are ideal for Class A fires where a potential Class C hazard exists. Unlike an ordinary water extinguisher, the misting nozzle provides safety from electric shock and reduces scattering of burning materials. This is one of the best choices for protection of hospital environments, books, documents and clean room facilities. In non-magnetic versions, water mist extinguishers are the preferred choice for MRI or NMR facilities or for deployment on mine sweepers.

Typical small lab fires (in a hood or on a bench) can easily be controlled by a dry chemical (ABC) or CO2 extinguisher provided that you are properly trained.

Summary of Fires and Fire extinguishers

Using fire extinguishers

You are not required to fight a fire. Ever. If you have the slightest doubt about your control of the situation DO NOT FIGHT THE FIRE.
1. Use a mental checklist to make a Fight-or-Flight Decision. Attempt to use an extinguisher only if ALL of the following apply:
The building is being evacuated (fire alarm is pulled)
The fire department is being called (dial 990 - T&T Fire Services, or 662 4707 - UWI Fire Safety).
The fire is small, contained and not spreading beyond its starting point
The exit is clear, there is no imminent peril and you can fight the fire with your back to the exit.
You can stay low and avoid smoke
The proper extinguisher is immediately at hand.
You have read the instructions and know how to use the extinguisher.

IF ANY OF THESE CONDITIONS HAVE NOT BEEN MET, DON'T FIGHT THE FIRE YOURSELF. CALL FOR HELP, PULL THE FIRE ALARM AND LEAVE THE AREA.

2. Whenever possible, use the "Buddy System" to have someone back you up when using a fire extinguisher. If you have any doubt about your personal safety, or if you can not extinguish a fire, leave immediately and close off the area (close the doors, but DO NOT lock them). Leave the building but contact a firefighter to relay whatever information you have about the fire.
3. Pull the pin on the fire extinguisher.
4. Stand several feet from the fire, depress the handle and sweep back and forth towards the fire.
Note: Do not walk on an area that you have "extinguished" in case the fire reignites or the extinguisher runs out! Remember: you usually can't expect more than 10 full seconds of extinguishing power on a typical unit and this could be significantly less if the extinguisher was not properly maintained or partially discharged.
The metal parts of CO2 extinguishers tend to get dangerously cold -- practice using one beforehand or have someone show you the proper way to hold one.
5. Direct the extinguisher at the base of the flames until the fire is completely out.
6. Recharge any discharged extinguisher immediately after use. If you discharge an extinguisher (even just a tiny bit) or pull the pin for any reason, call your campus safety officer to arrange a replacement.

Disclaimer: This format and content of this page has been modified to suit the needs of this department and contains guidelines for the use of fire extinguishers and is not meant to be a comprehensive reference. There are many circumstances that these guidelines can not foresee and you should recognize the inherent danger in relying solely on this information! If you would like to take a course on the proper use of fire extinguishers (including some hands-on training) your uwi campus Fire Safety Officer may be able to assist you. If not, try your local fire department's phone number for more information.

Source:
1. Webpage copyright 1995-2004 by Rob Toreki - Interactive Learning Paradigms Incorporated.(ILPI)
2. NFPA (The U.S. National Fire Protection Association)