Liquid Nitrogen Safety
College of Science and Technology
Central Michigan University
1. The extremely low temperature of the liquid can cause severe frostbite or eye damage upon contact. Items in contact with liquid nitrogen become extremely cold. Touching these items may result in torn flesh. Many substances become brittle upon contact with liquid nitrogen and may shatter when cold (such as common glass and large solid plastics), sending pieces of the material flying.
2. On vaporization it expands by a factor of 700; one liter of liquid nitrogen becomes 24.6 cubic feet of nitrogen gas. This can cause explosion of a sealed container. This release of nitrogen can also displace oxygen in the room and cause asphyxiation without warning.
3. Because the boiling point of oxygen is above that of nitrogen, oxygen can condense from the air into the liquid nitrogen. If dewars and insulated flasks containing liquid nitrogen are left uncovered for an extended period of time, liquid oxygen can build up to levels which may cause violent reactions with organic materials (i.e. a severe clothing fire could result).
1. Safety goggles (unvented) – Required at all times.
2. Face shield – Required when pouring or filling.
3. Insulating gloves (gloves should be loose fitting, so they can be thrown off if liquid pours inside them, or they should be elastic cuff insulated gloves). – Required when pouring or filling.
4. A lab coat or long sleeves is required to minimize skin contact. Also, trousers should be worn on the outside of boots or work shoes to prevent shoes filling in the event of a spillage. – Required when pouring or filling.
1. You must have Department approval prior to handling liquid nitrogen.
2. Always wear PPE when handling liquid nitrogen.
3. Use liquid nitrogen only in well ventilated places. Never dispose of liquid nitrogen by pouring it on the floor. It could displace enough oxygen to cause suffocation. Nitrogen is colorless and odorless – the cloud that forms when you pour liquid nitrogen is condensed water vapor from the air, not nitrogen gas.
4. Do not allow any liquid nitrogen to touch any part of your body or become trapped in clothing near the skin.
5. Do not touch any item that has been immersed in liquid nitrogen until it has warmed to room temperature.
6. Do not store liquid nitrogen in any container with a tight fitting lid. A tightly sealed container will build up pressure as the liquid boils and may explode after a short time. Use only approved unsealed containers. Do not store liquid nitrogen for long periods in an uncovered container. Use only fittings that have been designed specifically for use with cryogenic liquids as non-specialized equipment may crack or fail. Do not transport liquid nitrogen in wide-mouthed glass dewars or dewars not protected with safety tape.
7. Never dip a hollow tube into liquid nitrogen; it may spurt liquid.
8. Never ride in an elevator with liquid nitrogen! When using passenger elevators, use an elevator key to prevent the door from being opened by unauthorized persons. If a key is not available, then station a person at each floor to ensure no one enters.
9. Note that outside of normal working hours (M-F, 8:00 a.m. – 5:00 p.m.), no one is allowed to transfer liquid nitrogen from the Dow loading dock area without a second person present. Failure of a container or a large spillage could result in asphyxiation at a time when you are unlikely to be found or able to get assistance.
10. Always fill warm dewars slowly to reduce temperature shock effects and to minimize splashing.
11. Always make sure that containers of liquid nitrogen are suitably vented and unlikely to block due to ice formation.
12. Do not fill cylinders and dewars to more than 80% of capacity, since expansion of gases during warming may cause excessive pressure buildup.