Question: How did you hold the fire in your display pictures?

Daisy Shearer answered on 17 Mar 2022:

That’s one of my favourite demos! It’s called the propane bubbles demo 😊

So basically it starts off with a big tank full of water and washing up liquid. We have a can of propane gas which we pump into the tank which makes lots of bubbles filled with propane. Then, you need to soak your hand in the water as this protects it. You scoop up a big handful of bubbles filled with propane and then light them with a lighter and wooosh! You make fire in your hand.

What’s happening here is that we are showing a combustion reaction because the propane is flammable and is set alight by the heat (a small flame from a lighter) and the oxygen in the air when the bubbles get popped.

Soaking your hand with a layer of water protects it because water has a much higher ‘specific heat capacity’ than the propane which is just a fancy way of saying that it takes a lot more energy to heat up water than propane. So when the propane burns, the water can absorb all of the energy from the flames without heating up much, so you don’t get burned at all!

[Note: Please don’t try this experiment at home! I’m fully trained to demonstrate this experiment in a controlled environment with a full risk assessment.]

Here’s the demo in action for those interested: