How Do Safety Matches Work?

29th November 2017

Chemicals, Science

'How do safety matches work?' featured blog image

Safety matches are a common item in every household’s kitchen drawer. They’re a simple enough concept – strike the match head against the strip and voila. But there’s actually a lot of chemistry at work in this everyday object.

There are two types of matches: ones that are considered safe, and ones that can be ignited using any surface. The only difference is that in safety matches, the chemicals required to ignite are kept separate from each other. But before we understand how they work, we must first ask – how did they come in to being?

A row of safety matches on fire

The Lucifer Match

Safety matches have come a long way from their antecedent, the Lucifer match. According to an 1893 article in the Pacific Rural Press, the invention of the match is credited to Sir Isaac Holden, who capitalised on the need for instant fire at your fingertips.

It didn’t take long for the Lucifer match to gain popularity. They were sold in metal tins, and came with a piece of sandpaper to light against. The composition of Lucifer matches weren’t too dissimilar from matches today. But there was one ingredient that made a vital difference: white phosphorus.

A Gruesome History

While white phosphorus does make a cameo appearance in modern day safety matches, this is only as a small amount of vapour – but we’ll get into that later. In the early nineteenth-century, however, Lucifer matches heavily relied on white phosphorus as one of the main ingredients in the match head. White phosphorus is a very combustible and toxic material. Its pyrophoric properties means that it can spontaneously self-ignite. This is why it is commonly used as an incendiary weapon by the military.

Match factory worker with phossy jaw

Workers in match factories would often have to have their lower jaw removed after phosphorus poisoning

Similar to Napalm, white phosphorus is used in shells and grenades, igniting spontaneously to produce heat that is so intense that it melts skin from the bone. This chemical is also the culprit behind phossy jaw, an occupational disease caused by the inhalation of the chemical’s toxic fumes. The white phosphorus would attack the lower jaw, causing abscesses and even brain damage. The only treatment was to remove the entire jawbone, leaving the sufferer permanently disfigured. The other alternative was death from organ failure.

The unstable and toxic properties of white phosphorus meant that fatal accidents would occur every day: boxes of matches would suddenly ignite after being shaken or left in sunlight, and people would often breathe in the toxic fumes. Something had to be done about the dangerous Lucifer match.

Making a Change

Because of the public’s demand for and dependence on cheap matches that could be lit anywhere, it took more than 50 years after the dangers were identified to end the manufacturing of Lucifer matches. A combination of press coverage, public campaigning, and legislative change meant that in 1910, these deadly matches were finally replaced with a safer alternative.

A 19th century newspaper advert for Bryant & May's new safety matches

A 19th century newspaper advert showing the Lucifer match powerhouse, Bryant & May’s, moving towards safety matches.

Introducing safety matches…

Interestingly, the active ingredients that were present in Lucifer matches were still used in safety matches, but with one game-changing difference: the combustible chemicals were separated between match head and striking pad.

White phosphorus was eventually replaced with another allotrope: red phosphorus. Red phosphorus does not ignite in air where the temperature is below 240°C, unlike its predecessor which could spontaneously ignite at 30°C. This means that it is a much more stable element to use in a commonplace household item.

Ingredients in Safety Matches

We’ve already established that what constitutes safety matches is the fact that the combustible elements are kept separate from each other. But what are the purposes behind the ingredients?

The match head contains an oxidising agent, usually potassium chlorate, and sulphur. These chemicals do not ignite on their own, meaning that the match will not light from normal friction. This is because the striking surface contains the chemical needed for the potassium chlorate and sulphur to ignite: red phosphorus.

The match head also contains glue, which not only binds materials together but also serves as extra fuel. The wooden stick is covered in a layer of paraffin wax. This ensures that the flame will burn down the stick. The wood is also soaked in ammonium phosphate which stifles any afterglow. The striking surface and match head share one major ingredient: powdered glass. This is important because it’s what starts the whole process.

A pile of red phosphorus, which is an ingredient in safety matches

Red phosphorus replaced white phosphorus in matches because it was much more stable. It is contained in the striking surface of safety matches, not in the match head.

How Does It Work?

When the match head strikes the scratch pad, the glass-on-glass friction creates heat. This heat is enough to convert a small amount of red phosphorus into white phosphorus vapour.

Although white phosphorus spontaneously ignites, it would be a short-lived display if it weren’t for the oxidising agent in the match head. The small amount of white phosphorus begins to decompose the potassium chlorate, liberating oxygen so that the flame can continue to burn. The oxygen then combines with the sulphur so that it can also start to burn. This ignites the wood of the match, which the flame will stick to because of the paraffin wax.

All of these components are what allow the match to stay lit for long enough to light your favourite Yankee Candle.

Difference Between Safety Matches and Normal Matches

The only difference between safety matches and strike-anywhere matches is that the match head of the latter contains red phosphorus as well as an oxidising agent and sulphur. This allows it to ignite on any surface when friction creates heat.

In contrast, if you struck a safety match against a brick wall, for example, there would be no ignition because red phosphorus isn’t contained in the match head.

Did You Know…?

While match heads are commonly red, this isn’t because of the colour of the contained chemicals. The fact that it is the same colour as the red phosphorus is just a coincidence. The reason the match head is coloured is because dye is added to the tip in order to clearly indicate which end catches on fire.

Close up of a burning match

It’s obvious that matches have gone through a pretty gruesome evolution. It’s a relief that safety matches have come leaps and bounds from the days of Lucifer, and how something so tiny can be so remarkable.

Here at ReAgent, we love to unravel the scientific mysteries behind commonplace objects. In the past, we’ve looked into the chemistry of fireworks, and even fear! Why not subscribe to our newsletter to keep updated with these mind-blowing chemistry facts? It’s free!

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