Cryogenic liquids

Cryogenic liquids (also known as cryogens) are gases at normal temperatures and pressures. However, at low temperatures, they are in their liquid state. These liquids are extremely cold and have boiling points less than -150°C (- 238°F). Even the vapors and gases released from cryogenic liquids are very cold. They often condense the moisture in air, creating a highly visible fog. Different cryogens become liquids under different conditions of temperature and pressure, but all have two properties in common; extremely cold and small amounts of liquid can expand into very large volumes of gas. Everyone who works with cryogenic liquids must be aware of their hazards and know how to work safely with them.

Types of Cryogenic Liquids

Each cryogenic liquid has its own specific properties but most cryogenic liquids can be placed into one of three groups:

  • Inert Gases: Inert gases do not react chemically to any great extent. They do not burn or support combustion. Examples of this group are nitrogen, helium, neon, argon and krypton.
  • Flammable Gases: Some cryogenic liquids produce a gas that can burn in air. The most common examples are hydrogen, methane, carbon monoxide, and liquefied natural gas.
  • Oxygen: Many materials considered as non-combustible can burn in the presence of liquid oxygen. Organic materials can react explosively with liquid oxygen. The hazards and handling precautions of liquid oxygen must therefore be considered separately from other cryogenic liquids.

Personal Protective Equipment to be worn

  • Be sure to work in a well ventilated area to prevent oxygen deficient atmospheres under 19.5% oxygen.
  • Wear safety shoes when handling containers along with long sleeve shirts and trousers without cuffs.
  • ALWAYS wear a full face shield and splash resistant safety goggles. Contact lenses should not be worn.
  • Wear a lab coat and an apron when dispensing liquid nitrogen.
  • Wear insulated or leather gloves when handling liquid nitrogen or large, cold objects.

Handling Cryogenics Liquids

  • Never allow any unprotected part of the body to touch non-insulated pipes or vessels which contain cryogenic fluids. Tissue damage that results is similar to frostbite or thermal burns.
  • The extremely cold metal will cause flesh to stick fast and tear when one attempts to withdraw from it.
  • Use a suitable hand truck for container movement.
  • Do not drop, tip, or roll containers on their sides. Do not remove or interchange connections. If user experiences any difficulty operating container valve or with container connections discontinue use and contact supplier. Use the proper connection. DO NOT USE ADAPTERS.
  • Many substances become brittle and may shatter when cold, sending pieces of the material flying. Avoid common glass and large, solid plastics.

Storing Cryogenic Liquids

  • Store and use with adequate ventilation.
  • Do not store in a confined space.
  • Cryogenic containers are equipped with pressure relief devices to control internal pressure. Under normal conditions these containers will periodically vent product. Do not plug, remove, or tamper with pressure relief device for this could cause an explosion.
  • Containers shall be handled and stored in an upright position.
  • Small quantities of liquid nitrogen can be stored in Dewar bottles. Dewar bottles are hollow-walled glass-lined containers which provide excellent insulation.

Hazards of Cryogenic Liquids

  • Extreme Cold Hazard: Cryogenic liquids and their associated cold vapors and gases can produce effects on the skin similar to a thermal burn. Brief exposures that would not affect skin on the face or hands can damage delicate tissues such as the eyes. Prolonged exposure of the skin or contact with cold surfaces can cause frostbite. The skin appears waxy yellow. There is no initial pain, but there is intense pain when frozen tissue thaws. Unprotected skin can stick to metal that is cooled by cryogenic liquids. The skin can then tear when pulled away. Even non-metallic materials are dangerous to touch at low temperatures. Prolonged breathing of extremely cold air may damage the lungs.
  • Asphyxiation Hazard: When cryogenic liquids form a gas, the gas is very cold and usually heavier than air. This cold, heavy gas does not disperse very well and can accumulate near the floor. Even if the gas is non-toxic, it displaces air. When there is not enough air or oxygen, asphyxiation and death can occur. Oxygen deficiency is a serious hazard in enclosed or confined spaces. Small amounts of liquid can evaporate into very large volumes of gas.
  • Toxic Hazards: Each gas can cause specific health effects. Refer to the MSDS for information about the toxic hazards of a particular cryogen.
  • Fire Hazard: Flammable gases such as hydrogen, methane, carbon monoxide, and liquefied natural gas can burn or explode. Hydrogen is particularly hazardous. It forms flammable mixtures with air over a wide range of concentration. It is also very easily ignited. Oxygen-Enriched Air: When transferring liquid nitrogen through uninsulated metal pipes, the air surrounding a cryogen containment system can condense. Nitrogen, which has a lower boiling point than oxygen, will evaporate first. This evaporation can leave an oxygen-enriched condensate on the surface that can increase the flammability or combustibility of materials near the system, creating potentially explosive conditions. Equipment containing cryogenic fluids must be kept clear of combustible materials in order to minimize the fire hazard potential.
  • Liquid Oxygen Hazard: Liquid oxygen contains 4,000 times more oxygen by volume than normal air. Materials that are usually considered non-combustible (carbon and stainless steels, cast iron, aluminum, zinc, Teflon (PTFE), etc.) may burn in the presence of liquid oxygen. Many organic materials can react explosively, especially if a flammable mixture is produced. Clothing splashed or soaked with liquid oxygen can remain highly flammable for hours.
  • Embrittlement: Rubber, plastic, and carbon steel are some examples of materials that can be can become brittle and break with very little stress applied to them. Try to avoid using these materials when working with cryogenic. If these materials are used, perform an inspection before use.