Fire is the third leading cause of accidental deaths in the United States, yet most people ignore it. More than 150 workplace fires occur every day.
HOW FIRES START
Fire is a chemical reaction involving rapid oxidation or burning of a fuel. It needs three elements to occur:
FUEL - Fuel can be any combustible material - solid, liquid or gas. Most solids and liquids become a vapor or gas before they will burn.
OXYGEN - The air we breathe is about 21 percent oxygen. fire only needs an atmosphere with at least 16 percent oxygen.
HEAT - Heat is the energy necessary to increase the temperature of the fuel to a point where sufficient vapors are given off for ignition to occur.
CHEMICAL REACTION - A chain reaction can occur when the three elements of fire are present in the proper conditions and proportions. Fire occurs when this rapid oxidation, or burning takes place.
Take any one of these factors away, and the fire cannot occur or will be extinguished if it was already burning.
Fire Extinguisher Ratings: which kind of extinguisher should I use?
The National Fire Protection Association (NFPA) classifies fires into five general categories (U.S.):
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, hot plates 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 organometallic 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.
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. NFPA has a brief description of UL 711 if you want to know more.
Fire Extinguisher Multi-Class Ratings
Many extinguishers available today can be used on different types of fires and will be labeled with more than one designator, e.g. A-B, B-C, or A-B-C. Make sure that if you have a multi-purpose extinguisher it is properly labeled.
This is the old style of labeling indicating suitability for use on Class A, B, and C fires.
This is the new style of labeling that shows this extinguisher may be used on Ordinary Combustibles, Flammable Liquids, or Electrical Equipment fires. This is the new labeling style with a diagonal red line drawn through the picture to indicate what type of fire this extinguisher is NOT suitable for. In this example, the fire extinguisher could be used on Ordinary Combustibles and Flammable Liquids fires, but not for Electrical Equipment fires.
HOW TO PREVENT FIRES
Class A — Ordinary combustibles:
Keep storage and working areas free of trash Place oily rags in covered containers.
Class B — Flammable liquids or gases:
Don't refuel gasoline-powered equipment in a confined space, especially in the presence of an open flame such as a furnace or water heater.
Don't refuel gasoline-powered equipment while it's hot.
Keep flammable liquids stored in tightly closed, self-closing, spill-proof containers. Pour from storage drums only what you'll need.
Store flammable liquids away from spark-producing sources.
Use flammable liquids only in well-ventilated areas.
Class C — Electrical equipment:
Look for old wiring, worn insulation and broken electrical fittings. Report any hazardous condition to your supervisor.
Prevent motors from overheating by keeping them clean and in good working order. A spark from a rough-running motor can ignite the oil and dust in it.
Utility lights should always have some type of wire guard over them. Heat from an uncovered light bulb can easily ignite ordinary combustibles.
Don't misuse fuses. Never install a fuse rated higher than specified for the circuit.
Investigate any appliance or electrical equipment that smells strange. Unusual odors can be the first sign of fire.
Don't overload wall outlets. Two outlets should have no more than two plugs.
Class D — Flammable metals:
Flammable metals such as magnesium and titanium generally take a very hot heat source to ignite; however, once ignited are difficult to extinguish as the buring reaction produces sufficient oxygen to support combusion, even under water.
In some cases, covering the burning metal with sand can help contain the heat and sparks from the reaction. Class D exinguishing agents are available (generally as a dry powder in a bucket or box) which can be quite effective, but these agents are rare on the campus.
If you are planning a research project using a large amount of flammable metals you should consider purchasing a five or ten pound container of Class-D extinguishing agent as a precaution.
Pure metals such as potassium and sodium react violently (even explosively) with water and some other chemicals, and must be handled with care. Generally these metals are stored in sealed containers in a non-reactive liquid to prevent decay (surface oxidation) from contact with moisture in the air.
White phosphorus is air-reactive and will burn/explode on contact with room air. It must be kept in a sealed container with a non-reactive solution to prevent contact with air.
All of these metals are not uncommon in labs on the OU campus, but are generally only found in small quantities and accidental fires/reactions can be controlled or avoided completely through knowledge of the properties of the metals and using good judgement and common sense.
WHEN NOT TO FIGHT A FIRE
Never fight a fire:
If the fire is spreading beyond the spot where it started
If you can't fight the fire with your back to an escape exit
If the fire can block your only escape
If you don't have adequate fire-fighting equipment
In any of these situations,
DON'T FIGHT THE FIRE YOURSELF. CALL FOR HELP.
Types of fire extinguishers
Dry Chemical extinguishers are usually rated for multiple purpose use. They contain an extinguishing agent and use a compressed, non-flammable gas as a propellant.
Halon extinguishers contain a gas that interrupts the chemical reaction that takes place when fuels burn. These types of extinguishers are often used to protect valuable electrical equipment since them leave no residue to clean up. Halon extinguishers have a limited range, usually 4 to 6 feet. The initial application of Halon should be made at the base of the fire, even after the flames have been extinguished.
Water These extinguishers contain water and compressed gas and should only be used on Class A (ordinary combustibles) fires.
Carbon Dioxide (CO2) extinguishers are most effective on Class B and C (liquids and electrical) fires. Since the gas disperses quickly, these extinguishers are only effective from 3 to 8 feet. The carbon dioxide is stored as a compressed liquid in the extinguisher; as it expands, it cools the surrounding air. The cooling will often cause ice to form around the “horn” where the gas is expelled from the extinguisher. Since the fire could re-ignite, continue to apply the agent even after the fire appears to be out.
Here are some typical extinguishers and their uses:
Water extinguishers 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; see below.
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 halogl I; see below) 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. CO2 extinguishers are not approved for class D fires!
To get an idea for what could happen, take a look at this General Chemistry demonstration page that includes a QuickTime movie of a magnesium metal fire contained inside a block of solid CO2!
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. Both types of class D units are available through our on-line
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.
A few less-common extinguishers that are worth noting are:
halogl I extinguishers, like carbon dioxide units, are for use on class B and C fires. halogl 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 halogl 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 halogl I. In addition, FE-36 has zero ozone-depleting potential; FE-36 is not scheduled for phase-out wheras halogl 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 (see warning box below) or for deployment on mine sweepers.
MAGNETIC FIELD WARNING
If you work around extremely high field magnets such as magnetic resonance imaging (MRI) machines or nuclear magnetic resonance spectrometers (NMR's), you should only have non-magnetic fire extinguishers on hand. The magnetic field of an MRI or NMR machine is strong enough to make a steel cylinder fly across the room with lethal force.
Check out the potential fire hazards in your area. Is there an extinguisher available? Do you know how to operate it? Are your extinguishers suitable for the fires you may encounter? If not, you'll want to contact your campus or corporate
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.
HOW TO EXTINGUISH SMALL FIRES
Class A - Extinguish ordinary combustibles by cooling the material below its ignition temperature and soaking the fibers to prevent re-ignition.
Use pressurized water, foam or multi-purpose(ABC-rated) dry chemical extinguishers. DO NOT USE carbon dioxide or ordinary (BC-rated) dry chemical extinguishers on Class A fires.
Class B - Extinguish flammable liquids, greases or gases by removing the oxygen, preventing the vapors from reaching the ignition source or inhibiting the chemical chain reaction.
Foam, carbon dioxide, ordinary (BC-rated) dry chemical, multi-purpose dry chemical, and halon extinguishers may be used to fight Class B fires.
Class C - Extinguish energized electrical equipment by using an extinguishing agent that is not capable of conducting electrical currents.
Carbon dioxide, ordinary (BC-rated) dry chemical, multi-purpose dry chemical and halon* fire extinguishers may be used to fight Class C fires. DO NOT USE water extinguishers on energized electrical equipment.
* Even though halon is widely used, EPA legislation is phasing it out of use in favor of agents less harmful to the environment.
Class D - Extinguish combustible metals such as magnesium, titanium, potassium and sodium with dry powder extinguishing agents specially designated for the material involved.
In most cases, they absorb the heat from the material, cooling it below its ignition temperature.
NOTE: Multipurpose (ABC-rated)chemical extinguishers leave a residue that can harm sensitive equipment, such as computers and other electronic equipment. Because of this, carbon dioxide or halon extinguishers are preferred in these instances because they leave very little residue.
ABC dry powder residue is mildly corrosive to many metals. For example, residue left over from the use of an ABC dry powder extinguisher in the same room with a piano can seriously corrode piano wires.
Carbon dioxide or halon extinguishers are provided for most labs and computer areas on campus.
HOW TO IDENTIFY THE PROPER FIRE EXTINGUISHER
All ratings are shows on the extinguisher faceplate. Some extinguishers are marked with multiple ratings such as AB, BC and ABC. These extinguishers are capable of putting out more than one class of fire.
Class A and B extinguishers carry a numerical rating that indicates how large a fire an experienced person can safely put out with that extinguisher.
Class C extinguishers have only a letter rating to indicate that the extinguishing agent will not conduct electrical current. Class C extinguishers must also carry a Class A or B rating.
Class D extinguishers carry only a letter rating indicating their effectiveness on certain amounts of specific metals.
How to Use a Fire Extinguisher
Even though extinguishers come in a number of shapes and sizes, they all operate in a similar manner. Here's an easy acronym for fire extinguisher use:
P A S S -- Pull, Aim, Squeeze, and Sweep
Pull the pin at the top of the extinguisher that keeps the handle from being accidentally pressed.
Aim the nozzle toward the base of the fire.
Stand approximately 8 feet away from the fire and squeeze the handle to discharge the extinguisher. If you release the handle, the discharge will stop.
Sweep the nozzle back and forth at the base of the fire. After the fire appears to be out, watch it carefully since it may re-ignite!
Should your path of escape be threatened
Should the extinguisher run out of agent
Should the extinguisher prove to be ineffective
Should you no longer be able to safely fight the fire
...THEN LEAVE THE AREA IMMEDIATELY!
HOW TO INSPECT YOUR FIRE EXTINGUISHERS
Know the locations of the fire extinguishers in your work area.
Make sure the class of the extinguisher is safe to use on fires likely to occur in the immediate area.
Check the plastic seal holding the pin in the extinguisher handle. Has the extinguisher been tampered with or used before? Report any broken/missing seals/pins to the University Fire Marshal at 325-0545.
Look at the gauge and feel the weight. Is the extinguisher full? Does it need to be recharged?
Water, some foam, and dry chemical extinguishers have gauges indicating the pressure inside the extinguisher. The pressure needle should be in the "green" area (generally 100-175 lbs., depending on the type of agent).
CO2 (carbon dioxide) extinguishers are high pressure cylinders with pressures ranging from 1500 lb to 2150 lb. These extinguishers DO NOT have gauges and must be weighed by Fire Safety staff to determine the amount of contents remaining.
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.
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.
Pull the pin on the fire extinguisher.
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.
Again, proper training is usually required by state or federal OSHA!
Direct the extinguisher at the base of the flames until the fire is completely out.
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 or corporate Fire Marshal's office to arrange a replacement.
Care and Maintenance of Your Extinguisher
At least once a month (more often in severe environments) you should inspect your extinguisher. Ensure that:
The extinguisher is not blocked by equipment, coats or other objects that could interfere with access in an emergency.
The pressure is at the recommended level. On extinguishers equipped with a gauge (such as that shown on the right) that means the needle should be in the green zone - not too high and not too low.
The nozzle or other parts are not obstructed.
The pin and tamper seal (if it has one) are intact.
There are no dents, leaks, rust, chemical deposits and other signs of abuse/wear. Wipe off any corrosive chemicals, oil, gunk etc. that may have landed on the extinguisher.
Some manufacturers recommend shaking your dry chemical extinguishers once a month to prevent the powder from settling/packing. We are dubious this has any value (see this Ansul technical bulletin for a detailed description), but you are going to pick it up to inspect it anyway, so why not give it a good shake?
Fire extinguishers should be pressure tested (a process called hydrostatic testing) after a number of years to ensure that the cylinder is safe to use. Consult your owner's manual, extinguisher label or the manufacturer to see when yours may need such testing.
If the extinguisher is damaged or needs recharging, get it replaced immediately!
One more time: Recharge all extinguishers immediately after use regardless of how much they were used.