Liquid nitrogen is a dangerous material. The following is an excerpt from the Air Products Nitrogen Material Safety Data Sheet:

A back of the envelope calculation indicates that the entire contents of a 10 Liter dewar being spilled in a unventilated 274 square foot room with an 8 foot ceiling would reduce oxygen levels below the 19.5% level where Air Products recommends the use of a respirator. Since most classrooms are larger than this, suffocation does not represent a major danger. When transporting the liquid in a car, however, it is probably a good idea to open a window.

The possibility of freeze burns represents a much more serious danger and is therefore our first concern. This does not mean that the demonstration itself is dangerous, but it does mean you must be careful. Dangers include:

• Nitrogen can spatter (possibly in eyes) while being poured.

• Flying chunks of frozen objects could cause eye injury.

• Students (being children) will want to reach out and touch nitrogen or other cold objects. As mentioned above, contact with nitrogen can cause tissue damage, and this must be prevented.

Therefore specific safety precautions should include:

• Teachers must stress to their students the importance of not touching frozen objects or nitrogen.

• Wear goggles whenever pouring or dumping nitrogen. Nitrogen can spatter into the eyes, and potentially blinding pieces of frozen things can fly around when we drop it.

• Use a glove and / or tongs to handle any object going into or out of nitrogen and to carry the nitrogen dewar.

Teachers should familiarize themselves with the following first aid instructions (excerpted from the Air Products Nitrogen Material Safety Data Sheet) for cryogenic freeze burns just in case the worst happens:

If cryogenic liquid or cold boil off contacts a worker's skin or eyes, frozen tissues should be flooded or soaked with tepid water (105-115F, 41-46C). DO NOT USE HOT WATER. Cryogenic burns which result in blistering or deeper tissue freezing should be seen promptly by a physician.

Remember to stress the importance of not touching liquid nitrogen or frozen objects.

See also Liquid Nitrogen Safetygram (in pdf format - see below) from Air Products and Chemicals, Inc.

Note: the Liquid Nitrogen Safetygram above requires Adobe Acrobat Reader which is available for free download.

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