Flour bomb

Flour bomb

The classic high school flour bomb demonstration shows the explosive power of flammable powders under the right circumstances. Given a large enough suspension of combustible flour or grain dust in the air, a significant explosion can occur. For example, the 1998 explosion of the DeBruce grain elevator in Wichita, Kansas which killed 7 people.

Table of contents

1 Safety
2 Apparatus
3 Method to make bomb
4 Method for demonstration
5 Effect
6 External Links

Safety

Apparatus should be enclosed in safety screens.
Everybody should wear safety goggles.
Coffee tin needs to be wrapped in sticky back plastic or sellotape.
Pupils and staff to stand at least 2 metres back.
When lighting the candle and placing the lid on the coffee tin keep your head out the way.
Do not use a glass funnel.

Apparatus

500g coffee tin with lid (not too stiff a fit).

Funnel with bottom edge flat to put flour in - can be made from plastic and paper.

Single hole bung to put funnel through.

Small candle.

Bulb-type pipette filler.
One spatula of dry flour (does not work as well if damp).
Splint and matches.

Method to make bomb

Make a hole in the coffee tin the same size as your bung at approximately the same height as the centre of the flame of the candle.
Push the funnel into narrow end of the bung as far as it will go, then insert this into the hole in your coffee tin (funnel on the inside). Attach the pipette bulb to the narrow end of the funnel. There needs to make a tight seal.

Method for demonstration

Put a spatula of flour (cornflour, custard powder etc will do very well) into the funnel, blocking the tube from the pipette bulb.
Put the candle inside the coffee tin (approximately in the centre).
Light the candle carefully using the splint (making sure not to light the funnel).
Fit the lid securely, without too much force, and then quickly give the pipette bulb a rapid squeeze.

Effect

The large surface area of the carbohydrate (flour) means that it is rapidly oxidised. There is a loud WHOOMP and the lid flies off (normally vertically) about 4 feet up.

External Links

OSHA report on Wichita grain elevator explosion