FAQ's

Why does smoke come from a fire?

Let's say you have a nice fire going, and it has burned down to the point where what you see is a collection of hot "glowing embers." The fire is still producing a lot of heat, but it is producing no smoke at all. You might have gotten to this point either by starting with logs in a fireplace or by starting with charcoal. If you now toss a piece of wood, or even a sheet of paper, onto this fire, what you will notice is that the new fuel produces a lot of smoke as it heats up. Then, all of a sudden (often with a small pop), it bursts into flame and the smoke disappears. If you have a fireplace or wood stove, or if you have been around a lot of campfires, this little scene is very familiar to you. It tells you a lot about smoke -- let's look at what is happening.

There are four things that you find in any piece of wood:

• WATER - Freshly cut wood contains a lot of water (sometimes more than half of its weight is water). Seasoned wood (wood that has been allowed to sit for a year or two) or kiln-dried wood contains a lot less water, but it still contains some.
• VOLATILE ORGANIC COMPOUNDS - When the tree was alive, it contained sap and a wide variety of volatile hydrocarbons in its cells. Cellulose (a chief component of wood) is a carbohydrate, meaning it is made of glucose. A compound is "volatile" if it evaporates when heated. These compounds are all combustible (gasoline and alcohol are, after all, hydrocarbons -- the volatile hydrocarbons in wood burn the same way).
• CARBON - the amount of carbon in dry wood will vary depending on the species of wood, age of wood etc. It can be expected that 1 Kg of wood contains about 450 to 500 gm of Carbon.
• ASH - Ash is the non-burnable minerals in the tree's cells, like calcium, potassium and magnesium.

What Type of Fire Extinguisher do I need?

The Fire Extinguisher must be appropriate for the type of fire being fought. Multipurpose fire extinguishers, labeled ABC, may be used on all three classes of fire. If you use the wrong type of extinguisher, you can endanger yourself and make the fire worse. It is also very dangerous to use water or an extinguisher labeled only for Class A fires on a cooking-grease or electrical fire.

Depending on their intended use, portable extinguishers store specific "extinguishing agents," which are expelled onto the fire. The types of Fire Extinguishers include:

• PRESSURIZED WATER MODELS are appropriate for use on Class A fires only. These must never be used on electrical or flammable-liquid fires.
• CARBON DIOXIDE extinguishers contain pressurized liquid carbon dioxide, which turns to a gas when expelled. These models are rated for use on Class B and C fires, but can be used on a Class A fire. Carbon dioxide does not leave a residue.
• DRY CHEMICAL extinguishers are either stored-pressure models or cartridge-operated models. The stored-pressure models have a lever above the handle for operation. The cartridge-operated models require two steps: Depress the cartridge lever, and then squeeze the nozzle at the end of the hose. The dry chemicals leave a residue that must be cleaned up after use.
• AMMONIUM PHOSPHATE dry chemical can be used on Class A, B, and C fires, but should never be used on a fire in a commercial grease fryer because of the possibility of reflash and because it will render the fryer's automatic fire-protection system less effective.
• SODIUM BICARBONATE dry chemical, suitable for fighting Class B and C fires, is preferred over other dry-chemical extinguishers for fighting grease fires. Where provided, always use the extinguishing system first. This also shuts off the heat to the appliance.
• POTASSIUM BICARBONATE, UREA-BASE POTASSIUM BICARBONATE, and POTASSIUM CHLORIDE dry chemical are more effective and use less agent than sodium bicarbonate on the same fire.
• FOAM (or AFFF and FFFP) EXTINGUISHERS coat the surface of a burning flammable liquid with a chemical foam. When using a foam extinguisher, blanket the entire surface of the liquid to exclude the air.

What size Fire Extinguishers are available?

Portable extinguishers are also rated for the size of fire they can handle. This rating is expressed as a number from 1 to 40 for Class A fires and from 1 to 640 for Class B fires. This rating will appear on the label-- 2A:10B:C, for example. The larger the numbers, the larger the fire of a specific class on which the extinguisher can be used (but higher-rated models are often heavier - make sure you can hold and operate an extinguisher before you buy it). No number accompanies an extinguisher's Class C rating. The C on the label indicates only that the extinguisher is safe to use on electrical fires.

Extinguishers for Class D fires must match the type of metal that is burning. These extinguishers do not use numerical ratings. Extinguishers for Class D fires are labeled with a list detailing the metals that match the unit's extinguishing agent.

Fire Extinguishers Have Their Limits

Portable extinguishers are not designed to fight large or spreading fires. Even against small fires, they are useful only under certain conditions:

• The operator must know how to use the extinguisher.
• The extinguisher must be within easy reach, in working order, and fully charged.
• The operator must have a clear escape route that will not be blocked by fire.
• The extinguisher must match the type of fire being fought. (Extinguishers containing water are unsuitable for use on grease or electrical fires.)
• The extinguisher must be large enough to put out the fire. Many portable extinguishers discharge completely in as few as eight to ten seconds.

!!! Always be sure the fire department inspects the fire site, even if you think you've extinguished the fire !!!

Only Fight a Fire If ...

• ...the fire is small and contained. The time to use a fire extinguisher is in the early, or incipient, stage of a fire. Once the fire starts to grow or spread, it is best to evacuate the building, closing doors or windows behind you.
• ...you are safe from toxic smoke. If the fire is producing large amounts of thick, black smoke or chemical smoke, it may be best not to try to extinguish the fire. Neither, should you attempt to extinguish the fire in a confined space. Outdoors, approach the fire with the wind at your back. Remember that all fires will produce carbon monoxide and many fires will produce toxic gases that can be fatal, even in small amounts.
• ...you have a means of escape. You should always fight a fire with an exit or other means of escape at your back. If the fire is not quickly extinguished, you need to be able to get out quickly and avoid becoming trapped.
• ...your instincts tell you it's OK. If you do not feel comfortable attempting to extinguish the fire, don't try ­ get out and let the fire department do their job.

Fighting Small Fires on the Job

Fire extinguishers in the workplace should be placed conspicuously and within easy reach so they can be accessed quickly while a fire is still small.

Federal regulations require that employers who provide portable fire extinguishers in the workplace also provide training for their use. Used properly, portable fire extinguishers can save lives and property by putting out a small fire in the workplace or containing one until the fire department arrives.

It is essential that all employees be familiar with the proper use of portable extinguishers and know when and when not to use them. In the event of a fire, employees should respond in accordance with their company's fire-emergency plan. Most employees will evacuate. Certain trained and designated employees will evaluate the fire scene and, if the fire is small and conditions are reasonably safe, use a fire extinguisher to fight the fire. If the fire is large or conditions are unsafe, all employees will evacuate.

How do multi-class dry chemical fire extinguishers work?

If you ask any firefighter what it takes to create a fire, you will learn that you have to have three things:

1. A Fuel - some sort of combustible solid, liquid or gas
2. Oxygen to react with the fuel
3. Heat- there must be enough heat to get the fuel above its flash point. There is paper on your desk right now that is surrounded by oxygen. It does not burn unless you get the paper hot enough.

If you want to put out a fire, you need to remove one of the three elements. When you watch firefighters battling a forest fire, they generally try to remove fuel or heat. Either they pour water on the fire to reduce the temperature, or they try to bulldoze strips of bare earth to eliminate the fuel.

A carbon dioxide fire extinguisher works by eliminating oxygen and replacing it with carbon dioxide. You could do the same thing with just about any non-oxidizing gas (nitrogen, for example), but carbon dioxide is inexpensive and easy to store.

Another way to cut off oxygen is to throw a blanket over the fire. Covering the fire with dirt or sand does the same thing. You might have heard that you can put out a kitchen fire by throwing baking soda or salt on the fire. Throwing sand would do the same thing, but most people have more salt in their kitchens than they have sand.

Dry chemical fire extinguishers are by far the most common fire extinguishers in the home. They can handle all three types of fires you would find in a kitchen or workshop: combustible solids like wood or paper, combustible liquids like gasoline or grease, and electrical fires. The idea behind a dry chemical fire extinguisher is to blanket the fuel with an inert solid (similar to dirt or sand). A dry chemical extinguisher sprays a very fine power of sodium bicarbonate (normal baking soda), potassium bicarbonate (nearly identical to baking soda), or monoammonium phosphate. These solids coat the fuel and smother the fire.