Creating a Fireball – Pouring Water on an Oil Fire

Most people know the advice about never putting water on an oil fire. We joined Dr Peter Wothers on the roof of the Ri building in London to show exactly why.

Above the famous Lecture Theatre, the team set up a clear protective shield around a beaker filled with 150ml of oil. This was heated over a Bunsen until a small fire was burning. Wearing a fire protective suit, Dr Wothers then poured water from a small cup directly onto the fire.

The reaction is so violent because water and oil don’t mix. When the water is poured into the beaker of burning oil it sinks to the bottom and, due to the intense heat, vaporizes into steam almost instantaneously. With this phase change from a liquid to a gaseous state the water expands by up to 1700 times and forces the fire above it upwards. This oxygenates the oil and creates the huge flame you can see in the video.

Peter Wothers explains more:

“This is a great reaction to illustrate the topic of our second Christmas Lecture (Water), but it would also have done for Fire too if we had been presenting a fourth lecture. It is one of my favourite demos since it really rams home how dangerous it is to add water to an oil fire. I was never really aware of how large the flames are around me since I was busy concentrating on what I was doing!”

Devised to promote the 2012 Christmas Lectures, this is one of three large-scale, chemistry demos that were too big (or too dangerous!) to perform in the Ri Lecture Theatre in front of 400 young people.

This experiment was undertaken under the supervision of professionals and should not be replicated.

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