How Fire Starts

Fire is one of nature’s most powerful, yet also destructive, phenomena. It has served humans in many ways. Cooking and heating are its most obvious uses. It is also used for signaling, and as a source of heat for metalworking and ceramics. It can even inspire art, from flame dancing to pyrotechnic displays. However, the fire is most often feared when it threatens property or human lives. Fires are caused by both natural and human activities, with most being preventable.

A fire needs three things to start: a source of ignition, fuel and oxygen. If any one of these is missing, the fire won’t start. If it isn’t extinguished quickly enough, it will continue to spread and cause damage.

Class A: Ordinary combustible materials, such as wood, cloth, paper and some plastics. They burn with a short duration of flame, and produce soot. This includes cigarette and cigar smoke.

The heat energy of a fire transfers from the burning material to the surrounding air and from the air to the burning material. The heat also creates vapor in the form of smoke, which moves through openings in walls and doors. The vapor may also contain toxic gases, such as carbon monoxide, if it is incomplete combustion.

Most fires begin when a source of ignition, such as a lit cigarette or electrical spark ignites fuel, such as dry grass or wood. Once the fuel has heated up to its ignition temperature, it releases a chemical called carbon monoxide. The carbon monoxide mixes with the oxygen in the air to form a compound called carbon dioxide. This produces the familiar blue flame. It may also release a less familiar color, depending on the chemical composition of the fuel and other factors.

During the initial stage of combustion, the flames are small and sputter. Once the vaporized fuel reaches its ignition temperature, it expands rapidly, pushing outward against gravity and creating pressure within the burning room. This pressure causes the flames to “point” upward.

This expansion, and the downward force of gravity on the vaporized fuel, also help to explain why flames tend to move up through a chimney when burning inside a home. The vaporized fuel may also be forced out sideways by wind, and can puddle on the ground, creating a smoldering fire that can easily spread to other material.

When a flame is fully developed, it has spread over much if not all of the available fuel. The temperatures of the fuel and the oxygen supply reach their highest point, causing the damage and smoke known as heat damage. Once the flames are consumed, the temperature and oxygen supply decrease rapidly, and the fire dies out.

The advantages of fire are numerous, but the disadvantages are serious. The risk of fire increases with clutter in the home. Keep clutter to a minimum, particularly near heaters and fireplaces. Never hang towels or tea cloths near heaters, and make sure clothes are not drying on airers by a fire.