Andrea Zak, age 11, of Winnipeg, Manitoba, Canada, for her question:
How does striking light a match?
The two words match and safety go hand in hand. There are safety matches, designed to reduce the risk of fires. And a sensible person always thinks of safety when he or she strikes a match. But even the safest match is not foolproof. So when the flame has done its work, we kill it dead and make sure there is no smouldering afterglow. One sensible habit is to break the dead match stick in two, which makes sure that it has no secret heat to start up another blaze on its own.
The secret of a match is a clever chain reaction, based on chemical kindling points. In the moment it takes to strike a light, the operation goes from warm to warmer to a blazing flame. And each stage has its own secret kindling point.
There are many burnable substances and each catches fire at its own special kindling point temperature. Paper needs only the heat from a match flame. Sticks need the extra heat that comes from burning paper. Heavy logs need lots of heat from the burning sticks before they catch fire. This is why we use paper and sticks to get a log fire started.
Somewhat the same idea is used to make a match. But instead of paper and sticks, they use mixtures of burnable chemicals. One of the mixtures in the match head has a very low kindling point. All it needs is a little warmth created by friction. As you know, when you rub your finger back and forth on a smooth surface, the friction makes it warm. When we strike a match head on a rough surface, there is enough friction to activate one of its chemical mixtures.
Vapors, oxygen and warmth from this operation trigger the other chemicals in the match head to burst into flame. All it takes to start this chain reaction of burning chemicals is a little warmth created by friction. Safety matches are made to strike only on the rough patch provided on the package. Kitchen matches are made to strike on any rough surface so it's up to us to use a lot of careful common sense when we use them.
Many different chemicals and mixtures of chemicals can be used to create a strikeable match. As a rule, the manufacturers use mixtures of potassium chlorate and phosphorus sesquisulfide which have very low kindling points. Striking the match head creates enough friction heat to vaporize and ignite the phosphorus sesquisulphide. The heat from this stage decomposes the potassium chlorate, releases oxygen and enough extra heat to start the flame.
Manufacturers strive to make their matches as foolproof as possible. For example, a wooden match stick is soaked in borax or some other chemical that retards a smouldering afterglow. Bulges are built around match heads so that they do not rub against each other and ignite themselves in the box. However, so far nobody has invented a perfectly foolproof match so let's always beware.