Cryogenic materials are characterized by their extreme low temperatures. These temperatures are reached by forcing substances which have low boiling points into the liquid phase. These liquids are then stored in insulated pressure vessels.
Cryogenic materials pose a number of hazards. The extreme low temperatures associated with cryogenic liquids and gases can cause effects similar to thermal burns when they come in contact with the skin. Unprotected skin will adhere to metals and other types of materials cooled to these temperatures and will cause tremendous tissue damage if torn away.
Containing boiling liquids generates very high pressures. Cryogenic containers should be handled with all the precautions of pressure vessels.
If cryogenic materials are allowed to depressurize they will rapidly expand and have the potential to displace oxygen. Such a situation may or may not be observable. A rapid expansion of a cryogenic material will likely generate a fog in the air, but if the leak occurs slowly, the fog created by the cryogenic gas may not be noticeable. In such a case, only an oxygen monitoring system can provide any warning.
Certain cryogenic materials are themselves flammable. In addition, liquefied inert gases reach temperatures capable of condensing oxygen out of the air and creating unexpected oxygen enriched atmospheres. These situations are extremely hazardous as only a slight increase in oxygen concentration can create an explosive atmosphere.
Storage and Use
- Cryogenic liquid containers must be high pressure vessels with pressure relief valves.
- Store pressure vessels in a dry place and check periodically for ice formation which may block pressure relief valves.
- Keep away from ignition sources
- Store and work with cryogenic liquids in a well ventilated place. Ensure that the ventilation leads out of the building.
- If large volumes of cryogenic liquids are stored, an oxygen monitoring system must be installed.
- All parts of a system using cryogenic materials must be rated for the accompanying temperatures and pressures.
- A cryogenic system must have a pressure relief device for each segment of the system which is isolated by valves.
- Pre-cool receiving vessels to avoid temperature shock.
- Use tongs to place and remove items in cryogenic liquid.
- Consider that materials may become very brittle in extreme cold. Handle all items at low temperatures carefully.
- The eyes are very susceptible to damage from cold temperatures and should therefore be protected. Wear safety glasses and consider a face shield.
- Close fitting gloves will provide no protection from low temperatures. Wear loose fitting thermal gloves (such as potholders) which can be easily removed if contaminated.
- Watches, rings, or other adornments which can trap cryogenic liquids near the skin should not be worn when handling cryogenic liquids.
If contact with cryogenic material occurs, the freezing happens so quickly that the ice crystals are very small. This works in favor of the victim as the frozen cells may not rupture. The key to preventing permanent damage to the cells is to NOT rub the area. The affected area must be slowly warmed using methods which will not cause intercellular damage.