2024-04-30 11:08:51
But how and why does it work? Why does striking a piece of steel with a flint spark sparks, but striking two random stones does not?
All methods of starting a fire have a similar goal: to create enough heat to ignite the embers.
Flint and steel struck together can quickly generate such heat because the iron in the steel reacts with the surrounding air as it is ripped away by the flint, says Peter Sunderland, a researcher at the University of Maryland in the US.
According to him, this is how a classic pocket lighter works. Each flick of the wheel rubs the flint against the steel, igniting the butane fuel inside the lighter and creating a flame.
However, to understand why this combination is so effective, one must delve into the chemistry of oxidation. Oxidation occurs when a chemical element or compound combines with oxygen and changes its properties. When this process occurs with iron, it is called rusting. Using flint and steel to make a fire uses a side effect of oxidation – heat.
Early people made tools from flint, because this rock can be used quite conveniently to form arrowheads – and sharp blades. Flint is much harder than steel, so when struck together, small pieces of iron are chipped off the steel.
Iron is easily oxidized when exposed to air, but this process is usually very slow. For example, an abandoned car or agricultural equipment rusts only after many years.
However, these tiny particles of iron in the steel oxidize in a fraction of a second – even though they wouldn’t look rusty to the naked eye. This creates very hot sparks. The process happens so quickly because the pieces of iron have a much larger surface area than a solid piece of iron.
“The surface-to-volume ratio is important,” says Mr. Sunderland. “A small iron filing has essentially zero volume, but a large surface area.”
Thus, when a small piece of iron is chipped off, many iron atoms are suddenly exposed to the air and can be oxidized simultaneously. During a chemical reaction, a large amount of energy is quickly generated in the form of heat. If enough of these burning and hot iron filings fall into a pile of dry leaves or twigs, they can ignite such kindlings.
Turning sparks into flames can be tricky, so it’s helpful to have something that the sparks can ignite more easily to speed up the process. According to Mr Sunderland, steel shavings work well – they will catch fire when sparks fall on them. Historically, people have used a “charcoal cloth,” a charred piece of cloth that ignites easily and then slowly smolders, giving the embers around it time to ignite.
Before the widespread production of steel, people could extract sparks by breaking flint into other iron-bearing rocks, such as pyrite, better known as fool’s gold.
Other ignition technologies work on a similar principle. The magnesium fire splitter, a popular factory choice, takes advantage of the fact that magnesium burns at a very high temperature. And if we put magnesium shavings in a pile of kindling, and then put sparks over them, the fire would start quickly.
Matches have completely different chemical reactions, but their purpose is similar: to quickly generate a lot of heat and ignite a fuel source.
Sometimes this process happens by accident, says Sara McAllister, a mechanical engineering researcher at the US Forest Service’s Missoula Fire Science Laboratory. For example, wildfires can start when someone pulls a trailer with a chain on the road surface, causing sparks. Or colliding power lines create sparks that ignite dry grass.
“It’s all kind of in the same area: small, hot particles that go into the dry propellant,” McAllister concludes.
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2024-04-30 11:08:51