How Do Safety Matches Work?

How Safety Matches Light and Why They Are "Safe"

When you strike a match, the white cloud that is produced is smoke and phosphorus pentoxide.
When you strike a match, the white cloud that is produced is smoke and phosphorus pentoxide. Tim Oram / Getty Images

There's a lot of interesting chemistry going on in the small head of a safety match. Safety matches are 'safe' because they don't undergo spontaneous combustion and because they don't make people sick. You have to strike a safety match against a special surface in order to get it to ignite. In contrast, early matches relied on white phosphorus, which is unstable and likely to burst into flame in air.

The other downside to using white phosphorus is its toxicity. Before safety matches were invented, people became ill from chemical exposure.

The match heads of safety matches contain sulfur (sometimes antimony III sulfide) and oxidizing agents (usually potassium chlorate), with powdered glass, colorants, fillers, and a binder made of glue and starch. The striking surface consists of powdered glass or silica (sand), red phosphorus, binder, and filler.

  1. When you strike a safety match, the glass-on-glass friction generates heat, converting a small amount of red phosphorus to white phosphorus vapor.
  2. White phosphorus spontaneously ignites, decomposing potassium chlorate and liberating oxygen.
  3. At this point, the sulfur starts to burn, which ignites the wood of the match. The match head is coated with paraffin wax so the flame burns into the stick.
  4. The wood of a match is special, too. Match sticks are soaked in an ammonium phosphate solution that reduces afterglow when the flame goes out.

    Match heads are commonly red. This isn't the natural color of the chemicals. Instead, red dye is added to the tip of the match to indicate it's the end that catches on fire.

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    Helmenstine, Anne Marie, Ph.D. "How Do Safety Matches Work?" ThoughtCo, Sep. 11, 2017, thoughtco.com/how-do-safety-matches-work-607897. Helmenstine, Anne Marie, Ph.D. (2017, September 11). How Do Safety Matches Work? Retrieved from https://www.thoughtco.com/how-do-safety-matches-work-607897 Helmenstine, Anne Marie, Ph.D. "How Do Safety Matches Work?" ThoughtCo. https://www.thoughtco.com/how-do-safety-matches-work-607897 (accessed January 23, 2018).