Cryogenic substances

Gases can be liquefied by increasing pressure or by strong cooling. Gases that have become liquid (or solid, as in the case of carbon dioxide) at very low temperatures are cryogenic substances. The special risks associated with cryogenic substances stem from their low temperatures. These risks can be divided into:

• Effects on the environment they come into contact with, such as embrittlement of materials and freezing of limbs;
• Effects of pressure build-up due to rapid evaporation, such as explosion hazard of ampoules. In addition, anyone working with cryogenic substances must take into account all the other properties of the gas, such as the degree of oxygen displacement and flammability.

Which substances
The most commonly used cryogenic substances in hospitals are:

• Argon;
• Helium;
• Nitrogen;
• Oxygen.

When working with cryogenic substances, there must be sufficient personal protection and aids, including

• Tools, such as:
  - Pliers;
  - Tweezers;
  - Dippers (jars with a long stem).
• Personal protective equipment

Personal protective equipment
Instruct staff about personal protective equipment and ensure that they follow the following rules:

• Wear clean, dry clothing made from natural materials.
• Preferably cover arms and legs completely and wear closed footwear.
• Use a work apron as protection for clothes.
• Use special insulating gloves when there is a chance of cold gas drops falling on the hands. The gloves must be made of materials that do not become brittle at low temperatures.
• Also wear gloves when direct contact with cold parts of the system is possible.
• Use good eye protection, preferably full face protection, as the eyes are very vulnerable.
• Ensure that the protective equipment can be removed quickly if the extremely cold gas has come into contact with it. They must not fit too tightly under any circumstances.

Rooms containing cryogenic substances must be equipped with the following facilities:

• A warning sign by the entrance door;
• Sufficient ventilation with floor extraction;
• O2 detection and alarm.

The following safety rules apply to vessels containing cryogenic substances:

• Take into account the possibility of pressure build-up in vessels and parts of the installation. Make sure that the pressure relief valves are functioning. Portable vessels must therefore not be closed with a lid without overpressure protection.
• Whenever possible, place storage vessels in separate, central areas, and preferably connect them to an automatic filling system.
• Work with a hoist to remove heavy racks with sample from large storage vessels to prevent physical strain.
• Transport transport vessels with a transport truck. Never leave them unattended.
• Do not transport open vessels in a lift with people in it;
• Have vessels and filling systems periodically checked or inspected and maintained by the supplier or a maintenance service.
• Use only stainless steel or aluminium open dewars. Glass open dewars are not suitable for cryogenic liquids.
• Only use specially developed vessels for the storage of small quantities of cryogenic substances. Never use an ordinary thermos!
• Affix stickers to the vessels with the following data:
  - Risks;
  - Hazard symbols;
  - Procedure in the event of emergencies.

Supplier
Consult the safety information provided by the supplier on the cryogenic substances or on the equipment in question.