The lunatic craze sweeping social media at the moment involves young people pouring flammable liquid onto themselves and setting it alight. I can’t believe I’ve just written that, but that seems to be what they’re getting a kick from. Not to mention second-degree burns and a stay in hospital.
What they’re doing in the name of ‘fun’ is based on the property of liquids to give off flammable vapour, which ignites when it comes into contact with a heat source. The misguided teenagers often use a cigarette lighter, but other sources of ignition will do just as well – and that means you could innocently suffer the same fate using some very familiar household chemicals in the wrong combination of circumstances.
The lesson is that hazardous substance storage is an important consideration both in the home and at work. For example, air freshener sprayed in the presence of a naked flame such as a candle can cause the vapour to ignite. Standing beside a barbecue whilst wearing some kinds of spray-on sunscreen can ignite the vapour it gives off, burning the wearer.
What’s happening in all of these cases is that the vapour is being exposed to a heat source hotter than its flashpoint – the temperature at which its vapour will ignite. There doesn’t have to be a naked flame involved; a hot surface like a heating element, machinery and superheated air are all enough.
A liquid’s flashpoint is the lowest temperature at which it will give off enough vapour to burn at the surface of the liquid. With petrol, that can be under 5ºC. (Hard and fast rules don’t apply; the purity of the liquid in question can change the temperature). Flashpoints for different fuels vary widely, which is why our safe storage advice pages offer a table of temperatures. Remember, the higher the flashpoint temperature for any material, the less hazardous it is.