George Bradbury, age 11, of Scottsdale, Arizona, for his question:
What exactly is spontaneous combustion?
This is one of those splendid terms that is bound to impress your friends and kinfolk. "Spontaneous combustion" has a grand sound and somehow seems to promise a burst of excitement. And indeed it keeps that promise, though as a rule the excitement is not at all the kind we wanted.
Both the long words in this impressive term are descended from Latin ancestors. "Spontaneous" means willing or voluntary. "Combustion" means the combining, of fuel chemicals with oxygen with results which can range from a blazing campfire to the slow burning processes that go on within living cells. The addition of "spontaneous" gives a special meaning to "combustion." Burnable substances need heat to ignite and start the burning process. Ignition occurs when a substance reaches its kindling point. And every substance has its own kindling point, maybe high or maybe low.
Paper has a lower kindling point than chips of wood and chips of wood have a lower kindling point than solid logs. To start a campfire, we use a match to ignite some paper. The heat from its burning is enough to ignite the chips and the heat from the burning chips is enough to ignite the logs. These stages of ignition occurred because we added heat from outside sources. None of the fuels burst into flames spontaneously. But there are times when certain substances do ignite by themselves. This type of fire is spontaneous combustion.
Flammable materials are those substances that have very low kindling points. Hydrogen gas needs only a tiny spark to ignite it. At one time this lightest of gases was used to lift balloons, and its low ignition point led to many disasters. Modern balloons use helium gas, which is somewhat heavier but does not ignite readily. Some of the most flammable material is dust floating in the air. Coal mines contain pockets of this hazardous dust and so do grain elevators. A mere spark can cause the dust to ignite in a flash with a far reaching explosion.
Other substances may ignite without even a spark. The chemicals in rags soaked with oil or paint oxidize with the air and the oxidation process gives off heat. If the flammable rags are left in a closed closet, the heat accumulates until the rags reach their kindling point, and they burst into flame by spontaneous combustion. The chemical process of decay also generates heat, especially in a pile of wet straw. In spite of the moisture present, the heat may be great enough to ignite the vegetation. This is what makes a haystack suddenly burst into flame of its own accord.
The possibility of fire is a factor we must consider among other hazards in the home. Almost any kind of dust may be flammable, and it is never sensible to empty a container of dust into a furnace or incinerator. The added heat may ignite the dusty particles and cause an explosion. Rags that have been used for a paint job should never be left in a container where drafts of air cannot carry away their gathering heat. They should be taken outdoors and disposed of before they have time to ignite by spontaneous combustion.