Cryogenic liquids (or cryogens) are largely used in our School as cooling agents in a wide range of scientific experiments. Different cryogens are available with the most used ones being liquid nitrogen and helium. Similar to compressed gases, cryogens as well combine physical and chemical hazards.
Refer to the safety data sheet (SDS) for information about the hazards of a particular cryogen
The main hazards related to cryogenics liquids are:
- The extreme low temperatures (−196℃ for nitrogen and −269℃ for helium) may induce frostbites upon direct skin contact. Unprotected skin can stick to metals cooled by cryogenic liquids and tear when pulled away.
- All cryogenic liquids produce large volumes of gas when they evaporate. Just 1 L of liquid nitrogen produce 678 L of gas and 1 L of liquid helium produce 738 L of gas. The gas displaces the air from the room and the oxygen can decrease to hazardous levels thus leading to an asphyxiation hazard.
- The slow evaporation of cryogens and low temperatures associated with it may lead to an increase of oxygen concentration (oxygen condenses at −182℃) and create potentially explosive conditions.
- Plastic and rubber became brittle if cooled at cryogens temperatures. They easily break with little stress applied. These materials should be avoided when working with cryogens.
- Flammable: upon evaporation, liquid hydrogen can form an extremely flammable mixture with air.
- Oxidant: oxygen, although not flammable, will support and accelerate a fire. Furthermore, materials that are non-combustible (Teflon, aluminum, zinc, …) may burn in the presence of liquid oxygen.
- Toxic or Corrosive: with the release of large quantities of carbon monoxide gas from the liquid, death upon exposure is almost immediate.
You can check the chemical hazard symbols on our chemical hazards page.
Manipulation of cryogens
Cooling: You should immerse objects very slowly into cryogens to avoid splashes and spills. You should use tongs to place and remove them and remember:
You should always wear personal protective equipment (PPE) when handling cryogens
Transfer: Remember. Pressurized and non-pressurized cylinders are designed to store only one kind of cryogenic liquid!
You should NEVER fill a cryogenic cylinder with a cryogen different than the one it is designed for
When you have to transfer a cryogen from one flask to another, follow these basic rules to keep you safe:
- Check that cylinders and dewars are the right ones for the cryogen you are transferring.
- Wear closed or work shoes.
- Do not leave vessels unattended while filling them.
- When you fill a smaller vessel, be sure to secure it so that it cannot tip over.
- Pour cryogens slowly: this way, you’ll prevent splashes, spills and thermal stress to the vessel.
- Never overfill dewars.
Transport of cryogens
There are different sites at school where Static Storage Tanks (Figure 1 in the gallery) are available for you to refill your cylinders, either Pressurized or Non-Pressurized ones (Figures 2 and 3 in the gallery).
Full cylinders are quite heavy. Ask a colleague to help you moving the high capacity cylinders. Do not pull full cylinders but always push them so that they do not fall (on your colleague!).
If in your lab you have cylinders without wheels you should move them using specifically designed trolleys for transportation (Figure 4 in the gallery below for an example).
Transport in goods-lifts and elevators
At least two people should be involved if you have to transport cryogens in a goods-lift.
All cylinders travel ALONE in lifts
Access to the goods lift is restricted during transport (Figure 5 in the gallery). The goods-lift are provided with a string to prevent access. If the string is absent, you can print the following document (link) and attached it on the cylinder during transport.At departure floor, one of you loads and sent the goods lift to the destination floor where a second person is waiting to collect it.