Demonstration

The context of a fat-pan (chip-pan) catching fire is used to demonstrate the conditions required to start combustion, and how to put such a fire out safely.

Lesson organisation

For school use, this must only be done as a demonstration. The demonstrator must have practiced the demonstration beforehand until confident that the procedure can be done safely in front of a class, when it should take 10-15 minutes.

Apparatus Chemicals

The teacher will require:

Face shield

Heat-resistant gloves

Crucible (25 mm diameter), nickel or steel
 (Note 1)

Pipeclay triangle to support crucible (Note 1)

Tripod

Bunsen burner

Heat resistant mats (Note 2)

Safety screens (Note 3)

A small square of hardboard or aluminium

Test-tube, fixed securely to end of 1 metre pole (Note 4)

The class will require:

Eye protection

Cooking oil, 3 cm3 per demonstration

Refer to Health & Safety and Technical notes section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Teacher to wear face shield and heat resistant gloves. Class to wear eye protection and must be kept not less than 4 metres back. Safety screens must be positioned and secured to protect both students and the demonstrator. The experiment must not be sited below a light fitting. 

1 Wedge the nickel crucible firmly and upright in the pipe-clay triangle on the tripod. It must not tip over when the flame is smothered by the demonstrator. The wires of the triangle may need to be bent over the tripod.

2 Protect the demonstration bench from hot burning fat by covering with an array of heat resistant mats.

3 Arrange safety screens and secure in place so they protect both demonstrator and the class.

4 The test-tube should be held firmly, e.g. in a test-tube holder, and strapped to the end of a long pole (a metre rule will suffice) so that the tube will not fall off when engulfed in flame during the demonstration.

Procedure

a Place about 5 cm3 of water in the test-tube ready for use during the demonstration.

b Pour 3 cm3 of cooking oil into the crucible and place a lighted Bunsen burner beneath it.

c Once the oil catches fire, switch off the gas supply to the Bunsen burner and extinguish the flame by placing a small square of hardboard or aluminium over the crucible to simulate placing a tray over a burning chip pan to remove the oxygen from the fire.

d Explain that a damp tea-towel would also extinguish the fat-pan fire. In this demonstration this method is unsuitable, as it could knock the apparatus off the tripod, but for a real fat-pan fire it is a good method.

e Remove the square and light the Bunsen burner again until the cooking oil re-ignites.

f Switch off the gas supply to the Bunsen burner, and holding the pole with the test-tube containing water attached at arm’s length, add the water to the burning oil. This will cause a ball of fire to rise about a metre, effectively demonstrating the hazard of attempting to put out a fat-pan fire with water.

Teaching notes

The procedure described is hazardous and risks are made acceptable only by adherence to the restrictions and precautions advocated. In addition to the precautions described above:

the demonstration must NOT be done in a fume cupboard. 

the quantities prescribed must NOT be exceeded; do NOT be tempted to use more cooking oil. 

a squat crucible must NOT be used as it ejects the hot fat sideways. 

a porcelain crucible is NOT safe as it is liable to break.

This demonstration can be linked to the teaching of the ‘fire triangle’ as well as to the more general aspects of assessing risks and taking action to reduce risks to themselves and others. Chip pan fires cause one-fifth of all accidental dwelling fires in the UK each year. As well as the damage they can cause to people’s homes, these fires also injure around 4,000 people every year.

(Reproduced from CLEAPSS Guide, L195:’Safer Chemicals, Safer Reactions’, section 9.5 by permission of CLEAPSS®)

Health & Safety checked, 2016

Credits

This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

© Nuffield Foundation and the Royal Society of Chemistry

West Sussex fire and rescue service – kitchen safety document

Page last updated October 2015

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