HOW FIRES START
Fire is a chemical reaction involving rapid oxidation or burning of a fuel. For a fire to occur, three elements must be present. Removal of any one of these elements will cause the fire to go out.
- 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.
- Fuel-Fuel can be any combustible material-solid, liquid or gaseous. Solids and liquids must give off vapors or gas before they will burn.
- Oxygen-The air we breathe is about 21 percent oxygen. Fire only needs an atmosphere of 16 percent oxygen.
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.
Fires are classified into five (5) classes. They are described below:
A fire extinguisher labeled with letter “A” is for use on Class A fires. Class A fires are fires that involve ordinary combustible materials such as cloth, wood, paper, rubber, and many plastics.
A fire extinguisher labeled with letter “B” is for use on Class B fires. Class B fires are fires that involve flammable and combustible liquids such as gasoline, alcohol, diesel oil, oil-based paints, lacquers, etc., and flammable gases.
A fire extinguisher labeled with letter “C” is for use on Class C fires. Class C fires are fires that involve energized electrical equipment.
A fire extinguisher labeled with letter “D” is for use on Class D fires. Class D fires are fires that involve combustible metals such as magnesium, titanium and sodium.
A fire extinguisher labeled with letter “K” is for use on Class K fires. Class K fires are fires that involve vegetable oils, animal oils, or fats in cooking appliances. This is for commercial kitchens, including those found in restaurants, cafeterias, and caterers.
Generally, you can tell with a glance which type of fire extinguisher is hanging on the wall just by the shape. Check the labels of the extinguishers in your area and note the color and shape/size of the extinguisher. This may help if someone runs in to help you fight a fire with the WRONG extinguisher (i.e. water on an electrical fire)-you can stop them before they are injured or make matters worse.
|ABC rated multi-purpose dry chemical extinguishers are the most common, particularly in the corridors of commercial and academic buildings. They are RED in color and have either a long narrow hose or no hose-just a short nozzle. These extinguishers are light weighing between 5-25 pounds.|
|Pressured Water Extinguishers
Pressurized water extinguishers are no longer commonly found in commercial settings. These extinguishers are chrome metal in color, have a flat bottom, have a long narrow hose and are quite large. They hold 2 ½ gallons of water and some have foam added. These extinguishers have a pressure gauge and an air valve similar to that on a car or bicycle tire.
|CO2 Fire Extinguishers
Carbon Dioxide extinguishers are filled with non-flammable carbon dioxide gas under extreme pressure. You can recognize a CO2 extinguisher by its hard horn and lack of pressure gauge. The pressure in the cylinder is so great that when you use one of these extinguishers, bits of dry ice may shoot out the horn.
CO2 cylinders are red and range in size from 5 lbs to 100 lbs or larger. In the larger sizes, the hard horn will be located on the end of a long, flexible hose.
CO2 ‘s are designed for Class B and C
(flammable liquid and electrical) fires only.Carbon Dioxide is a non-flammable gas that extinguishes fire by displacing oxygen, or taking away the oxygen element of the fire triangle. The carbon dioxide is also very cold as it comes out of the extinguisher, so it cools the fuel as well. CO2’s may be ineffective at extinguishing Class A fires because they may not be able to displace enough oxygen to successfully put the fire out. Class A materials may also smolder and re-ignite.CO2’s will frequently be found in laboratories, mechanical rooms, kitchens, and flammable liquid storage areas.
|Class D Extinguishers
Certain metals are extremely combustible and must be used with caution and appropriate safety measures. These metals include magnesium, potassium, sodium titanium, alkyllithiums, Grignards, and diethylzinc. These chemicals react violently with water, air, and other chemicals and cause class D fires, which burn at high temperatures. As such, typical fire extinguishers are not sufficient for this type of fire; labs working with combustible metals must have a type D extinguisher available.
|D extinguishers contain a sodium chloride or graphite metal-based powder. When discharged on a fire, the heat causes the powder to cake and form a crust which excludes air and dissipates the heat.|
|The type of class D extinguisher needed depends on the flammable metals present in the room. Lithium and lithium alloy metals require the graphite extinguishers (Lith-X extinguishers), while the magnesium, sodium, potassium, uranium and powdered aluminum fires are better extinguished using the sodium chloride based extinguishers (Met-L-X extinguishers).|
|Occasionally, in place of extinguishers, a dry medium, a graphite based powder known as Pyrene G-1., is kept in buckets near the work area for extinguishing fires. If there is concern about the chemicals discharged from the extinguishers, information regarding specific extinguisher types is available on the Extinguisher MSDS [link] page.|
|Class K Fires
Until recently, most commercial deep fat fryers and the range hoods and portable fire extinguishers in commercial kitchens were designed for use with animal-fat based oils and grease. Due to a number of different factors, the cooking industry has switched to the use of vegetable based oils and greases. These vegetable based oils and greases cook at a higher temperature than the equivalent animal fat based products. Once a fire starts in a deep fat fryer it cannot always be extinguished by traditional range hoods or portable fire extinguishers using Class B fire extinguishing products.
|A word on Halon Extinguishers
Under the Clean Air Act, the U.S. banned the production and import of virgin halon’s 1211, 1301, and 2402 beginning January 1, 1994 in compliance with the Montreal Protocol on Substances That Deplete the Ozone Layer. Recycled halon and inventories produced before January 1, 1994, are now the only sources of supply.It is legal to continue to use your existing halon system. It is even legal to purchase recycled halon and halon produced before the phase out to recharge your system.However, due to the fact that halons deplete the ozone layer, users are encouraged to consider replacing their system and making their halon stock available for users with more critical needs through recycling.
RULES FOR FIGHTING FIRES
Fires can be very dangerous and you should always be certain that you will not endanger yourself or others when attempting to put out a fire. For this reason, when a fire is discovered:
- Assist any person in immediate danger to safety, if it can be accomplished without risk to yourself.
- Activate the building fire alarm system AND notify the fire department by dialing 911 (or designating someone else to notify them for you). When you activate the building fire alarm system, it will sound the building alarms to notify other occupants, and it will shut down the air handling units to prevent the spread of smoke throughout the building. The fire alarm does NOT set off the sprinklers.
- Only after having done these two things, if the fire is small, you may attempt to use an extinguisher to put it out.
However, before deciding to fight the fire, keep these rules in mind:
Know what is burning. If you don’t know what is burning, you don’t know what type of extinguisher to use. Even if you have an ABC extinguisher, there may be something in the fire that is going to explode or produce highly toxic smoke. Chances are, you will know what’s burning, or at least have a pretty good idea, but if you don’t, let the fire department handle it.
The fire is spreading rapidly beyond the spot where it started. The time to use an extinguisher is in the incipient, or beginning, stages of a fire. If the fire is already spreading quickly, it is best to immediately isolate the fire by closing any doors to the burning area and evacuate the building. DON’T FORGET TO CALL THE FIRE DEPT!
REMEMBER 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. 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 and the fire alarm is being pulled
- The fire department is being called (dial 911or direct FD direct number).
- 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 the smoke.
- The proper extinguisher is immediately available.
- You have read the instructions and are familiar in the extinguishers use.
WHEN IN DOUBT-DON’T WAIT–JUST GET OUT
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
USING A FIRE EXTINGUISHER
Using a fire extinguisher, regardless of the type is simple and straightforward. The best way to remember the process is to use the acronym PASS
|P… Pull the pin.|
|A… Aim the extinguisher nozzle at the base of the flames.|
|S… Squeeze trigger while holding the extinguisher upright.|
|S… Sweep the extinguisher from side to side, covering the area of the fire with
the extinguishing agent.
Using a Class D fire extinguisher is slightly different from using the typical PASS technique:
Pull the pin. Holding the extinguisher with the nozzle pointing away from you, pull out the pin (usually located below the trigger).
Hold nozzle over fire. The 6-foot reach of the extension applicator hose and the squeeze grip valve allows placement of the dry powder exactly where it will be most effective. Remember – extinguishers are designed to be operated in an upright position. Always hold the extinguisher vertically. Never cradle it horizontally or at an angle. If the extinguisher is too heavy to hold properly, place it on the floor next to you and operate.
Squeeze the discharge lever. Squeeze slowly and evenly. This action will release the dry chemical and expel it through the discharge nozzle.
Apply the dry powder. Completely cover the burning metal with a thin layer of powder. Once control is established, take a position that is in close range. Throttle the stream with the nozzle valve to produce a soft, heavy flow. Cover the metal completely with a heavy layer of powder. Be careful not to break the crust formed by the powder. Slowly open the nozzle of the extinguisher.
Halotron I extinguishers, like carbon dioxide units, are “clean agents” that leave no residue after discharge. Halotron I is less damaging to the Earth’s ozone layer than Halon 1211 (which was banned by international agreements starting in 1994). This “clean agent” discharges as a liquid, has high visibility during discharge, 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. These superior properties of Halotron I come at a higher cost relative to carbon dioxide.
FE-36™ (Hydrofluorocarbon-236fa or HFC-236fa) is another “clean agent” replacement for Halon 1211. This DuPont-manufactured substance 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 whereas Halotron I production is slated to cease in 2015. A 100% non-magnetic CleanGuard model is now available (see the warning box below).
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.
Should you have any questions please contact the Lake Grove Fire Marshal’s Office at 516-807-6412 or your local fire department.