The Mechanism of Starting a Fire
If you put the flame of a lighted match under a piece of wood, you can
be sure that most of the time the wood will not catch fire. Even if
you dip a lighted cigarette into a pan of lubrication oil, it is very
unlikely that the 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 the 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 the 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 the Fire Triangle)
- Next, the source of heat, like a naked flame, must meet with the
combustible for a certain amount of time.
- The combustible must be able to absorb a considerable amount of heat
from the heat source in order to decompose. Combustibles that can burn
are usually organic compounds containing carbon. When the heat reaches
the combustible, the latter will give off gases due to the decomposition
of its material structure. Some of these gases are combustibles
themselves. Water vapour may also be given off.
- The wood becomes drier and drier. The gases given off by the
decomposition of the wood will catch fire by themselves. The heated
wood keeps on giving out combustible gases as long as it is heated.
- With the additional heat given off from the burning of the gases in
the wood, the heat becomes more intense. More parts of the wood are
heated, and more combustible gases emerge. The fire keeps getting bigger
and bigger until the whole piece of wood is consumed.
- If this bigger source of heat from the burning of the piece of wood is
able to contact other combustibles, then the fire will spread to the
whole house or building.
In the next post we will be looking at the sources of heat and fuel.
If you need any assistance with protecting your home or business we are always here to help.
Yours In Fire Safety