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The Mechanism of Starting a Fire
If you put
flame of a lighted match under a piece of wood, you can be sure that most of time wood will not catch fire. Even if you dip a lighted cigarette into a pan of lubrication oil, it is very unlikely that pan of oil will catch fire.
So how does a fire actually start?
To answer this question, we must know how a fuel burns. A piece of wood can be considered a fuel. The carpet fabric on floor of your house is also a fuel. But why does some fuel burn so easily while others do not? How does a fuel burn?
Taking a piece of wood as an example, below is sequence of events that happen when a fire occurs.
· First, there must be a source of heat, a combustible or fuel present, and sufficient oxygen. (Remember Fire Triangle) · Next, source of heat, like a naked flame, must meet with combustible for a certain amount of time. · The combustible must be able to absorb a considerable amount of heat from heat source in order to decompose. Combustibles that can burn are usually organic compounds containing carbon. When heat reaches combustible, latter will give off gases due to decomposition of its material structure. Some of these gases are combustibles themselves. Water vapor may also be given off. · The wood becomes drier and drier. The gases given off by decomposition of wood will catch fire by themselves. The heated wood keeps on giving out combustible gases as long as it is heated. · With additional heat given off from burning of gases in wood, heat becomes more intense. More parts of wood are heated, and more combustible gases emerge. The fire keeps getting bigger and bigger until whole piece of wood is consumed. · If this bigger source of heat from burning of piece of wood is able to contact other combustibles, then fire will spread to whole house or building.
Looking at Sources of Heat and Fuel
The obvious sources of heat are electrical heaters, electrical light bulbs, ovens, open flames of gas stove, electrical sparking, friction caused by rubbing, and so on.
Those that are not obvious are often things that will cause accidental fires. Electrical wiring is one of them. A good practice for home is to check electrical wiring conditions. This is especially so for old houses. The insulation of old wiring and components usually deteriorates with age, and contacts with dust, oil and moisture in environment. Some may have already cracked, exposing bare metal parts to environment. Electrical conductors do become corroded and contacts can become loose. This can cause sparking and overheating.
Sometimes, a fire is burning at its correct place, for example, at a stove. If there is an accidental spillage of fuel somewhere, it can cause flame to spread to another place. LPG hose leaks can cause a fire from gas stove to spread to hose and surrounding furniture. Leaking kerosene stove with dripping kerosene can cause fire from stove to spread to table or floor. Sometimes accidental breakage of a bottle of a spirit lamp may splash fuel all around and cause a fire to spread rapidly.
Accidents like these do happen, but they can still be avoided.
None of these fires can occur if there is no fuel to catch fire. Careful segregation of heat from fuel will ensure that fires will not spread. Even if it were to start, it will not be sufficient for fire to spread. When dealing with open fires like these, it is essential that no other combustible materials be nearby. So even if there is an accidental spillage, effects could be minimized.
The presence of a rich oxygen source can often cause a spontaneous fire. Chemicals like potassium permanganate, hydrogen peroxide can produce oxygen under certain conditions. These chemicals are often kept in homes for medical purposes. Sometimes oily rags throw around place can catch fire by themselves because of chemical reactions.
Storage of chemicals must be controlled because mixing of certain chemicals sometimes produces heat. Storage of paint, thinner, turpentine, methylated spirit and other solvents must also be well controlled. It is good to be aware of chemicals we use around house. Nail polish, lighter fluid, aerosol for paint or insecticide may contain very volatile inflammable materials.
Aerosols must be used carefully. Small particles are easily combustible. Even organic powders can be dangerous. A bowl of flour is very safe by itself, but if powder is allowed to be blown in air to form a haze, it can be easily ignited if there is a source of heat.
The sun can also produce a tremendous amount of heat. We experience this when we step into a car exposed to afternoon sun. It may just need a small quantity of extra heat to start a fire. Looking around for ways of reducing chances of oxygen-rich atmosphere forming anywhere around fuel and heat can help a lot in preventing unwanted fires from happening. However, sometimes it is unexpected that causes fires...
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Many years of working experience in Marine, Facilities, Construction has given the author material for writing e-books and articles related to engineering, and management. Subscribe to facworld ezine More information at Marine and M & E
