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Custard Powder Explosion
AKA: Dust Explosion

Summary

Custard powder is blown through a candle flame to create a fireball.

Operation

This demonstration is often used to show how the energy contained in foods can be released through burning. It can also be used in lessons involving 'rates of reaction' and 'particle size'.

There are many methods for a successful fireball, variations can be found on a number of websites and guides. All methods use the same principle however and involve blowing dry powder (usually custard powder) into a naked flame.

Simple setups involve a length of Bunsen tube connected to a wide straw inside which is a quantity of dry custard powder. The tube must be sufficiently long to ensure the blower is not too close to the flame. The straw needs to be firmly clamped and pointing upwards and away from the audience. A candle is lit and clamped above the end of the straw and the powder blown upwards either by using a balloon or foot pump or by mouth (blow, don't suck!) This should result in the powder igniting as it is propelled from the straw.

Other methods incorporate an empty metal tin with or without lid. An empty and clean treacle or syrup tin works well.

A few tea-light candles are lit and placed into the bottom of the tin and a bent glass tube is used in place of the straw. The tube needs to be securely fitted into the tin to make sure it will not fall over when air is blown through. Again a long enough length of tubing will ensure the operator will not get burned or covered in powder. Some methods include leaving the lid on the tin so that it blows off with some force when the powder ignites.

A glass funnel may be attached to a length of Bunsen tubing and held firmly in a clamp stand as another alternative method. This takes less time to set up each time and can be as effective as the other methods. If the powder has trouble catching, it may be too damp or if only some is catching, the flame may need to be placed closer to the opening where the powder is blown from. Some teachers may use a clamped Bunsen burner on a yellow flame instead of a candle so that the flame area is larger.

Other powders can be used such as cornflour, regular flour or icing sugar. Projected flames can be compared when using different powders, the flame size and shape may be affected by how much energy is contained in the food. Glucose burns in oxygen to produce carbon dioxide, carbon monoxide and water...

C6H12O6 + 5O2 2CO + 4CO2 + 6H2O

This is a relatively safe demonstration as long as common sense is followed. Keep viewers far enough away from the demonstration area and behind a safety screen. The operator should wear safety glasses and not be too close to the demonstration equipment. Ensure the powder will be blown straight upwards and that there is nothing hanging above the area which could catch fire.

In essence, ensure that no person or property can be harmed by the flame.

Ensure that the custard powder is not inhaled accidentally before the straw is blown.

Wheaten based custard powder and the egg in some custard powders may be an allergen to some people – ensure that no-one viewing the demonstration has these allergies.

Never use any other powders including metal powders which may ignite very violently.

If all goes well, the demonstration definitely has the 'wow' factor but also can provoke serious scientific debate. It can be used in both Chemistry and biology lessons and also as an end of term demonstration to send them off on holiday with a bang!

Safety

 CautionThe contents of this page are for information only. Please refer to CLEAPSS or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.

Follow the safety guide above and do a risk assessment before attempting this demonstration.