– Spontaneous Combustion?


I started oil painting again recently. I was quickly reminded that the mediums we use, odorless spirit minerals, etc., can SPONTANEOUSLY COMBUST into flames.

HOW is this possible? Something about oxygen?? I was trying to sleep and was scared that my whole house was gonna catch on fire. So that was cool.

In: Chemistry

Certain petroleum products when exposed to air will react with oxygen. As this reaction takes place, it produces heat. If it gets hot enough it will ignite.

It’s mostly risky when you have a lot of the substances all in one spot without a way for heat to escape. Piles of oily rags or rags soaked in mineral spirits are common culprits, as a lot of the spirits will be in one spot heating up, and air can’t circulate through to cool it down.

It’s prevented by removing oxygen (closing your mineral spirit can), dilution, and providing ventilation so heat can escape easily.

Volatile compounds like those in oil painting are called hydrocarbons. When left unattended, they slowly undergo the process called *oxidation.* This is essentially the loss of electrons of a given substance. This often results in the breaking of chemical bonds, a process which releases heat. If that heat is unable to dissipate, it can cause the substance in question to light on fire.

This is possible when these substances are in close contact with a very combustible substance (oily rags are a decent example of this).

Many chemical reactions require a bit of energy to “kick start” the reaction. Sometimes that required kick start is very large, for instance setting off C4 explosive accidentally is hard because it requires a large amount of energy in a small space. Other times the kick start is much smaller. In some cases, the required kick start is so small that it could be caused by almost anything; the smallest amount of heat or vibration would be enough to start the reaction. When a reaction requires so little energy to start that it could happen in normal conditions, that is usually considered a spontaneous combustion. An example of this might be a natural gas leak that fills a house with just the right combination of air and flammable gas; the slightest spark could start the reaction.

There are also chemical reactions which don’t require any kick start at all, they will occur as soon as the chemicals are mixed together regardless of outside vibrations, heat or other sources. These reactions can also be considered spontaneous combustion, but they rarely occur by surprise, since you wouldn’t want to keep those chemicals anywhere near each other. Many types of rocket fuel work like this and so are very carefully kept in separate tanks.