[ELI5] How come air can extinguish a fire (e.g. blowing a candle) but also ignite it (e.g. blowing a spark)?

Question

[ELI5] How come air can extinguish a fire (e.g. blowing a candle) but also ignite it (e.g. blowing a spark)?

In: 2

Answer 1

There are already some good answers, but I want to highlight a big difference between the candle and the “spark”.

With the candle, the wax is not burning in the solid or even liquid state. It must first vaporize and mix with air (oxygen) to burn. Once the wax is in vapor form, it mixes with air fairly easily. As others have said, when you blow on the candle it takes heat away and the vaporized wax fuel away.

If the spark is from a small piece of wood or other organic mater, then it is mostly carbon. The carbon is actually oxidizing (or burning) in the solid form. Since it’s solid, it is very hard for air to mix with it. Blowing on it gets more oxygen touching the carbon, so the carbon can burn faster. Since it’s a solid, the fuel and heat aren’t just blown away like with the vaporized candle wax.