Cryogenic Gas Hazards

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• Extreme Cold Hazard: Cryogenic gases, liquids, vapors can become so cold that they cause injuries equivalent to third degree burns or a thermal burn. Brief exposures may not affect the face's or hands' skin but can damage delicate tissues like the eyes. Continuous breathing of extremely cold air can damage the lungs. Prolonged contact of the skin with cold surfaces can cause frostbite, which leads to intense pain when frozen tissue thaws. The skin when not protected can stick to metal that is cooled by cryogenic liquids and when pulled away the skin can tear. Even non-metallic materials become very dangerous to touch at very low temperatures.
• Asphyxiation: A cryogenic gas will displace large quantities of air as it evaporates. Asphyxiation is caused due to oxygen displacement. In other words, a large quantity of gas displaced with evaporation of cryogenic liquid can result in asphyxiation. When cryogenic liquids form a gas, the gas is very cold. It is also heavier than air. This cold, heavy gas does not disperse very well and can group together in surrounding areas and even if the gas is non-toxic, it displaces air. Total displacement of oxygen by carbon dioxide, will result in unconsciousness, followed by death. Oxygen deficiency is a serious hazard in enclosed or confined spaces, leading to asphyxiation which is noticed in terms of nausea, dizziness, vomiting, loss of consciousness, and death. Such symptoms usually occur without any warning.

• Toxic hazards: Chemical toxicity hazards are faced when entering an area that has been used to store cryogenic liquids if proper ventilation is not employed. Though most of the commonly used cryogenic gases are considered to be of low toxicity, but still they can lead to specific health problems. Some gases like carbon monoxide, fluorine, and nitrous oxide are toxic and hence it is advisable to check the properties of the gases that are being used. For example, liquid carbon monoxide can generate large quantities of carbon monoxide gas, which can cause death almost immediately.

Fire hazard: Flammable cryogenic gases like methane, hydrogen, carbon monoxide, liquefied natural gas can burn or explode. Of all these gases, hydrogen is particularly more dangerous it is easily ignited as it forms flammable mixtures with air over a wide range of concentration. Fire or explosion occurs when evaporation and vapor buildup. Liquid oxygen, though not a flammable gas, can accelerate combustion when combined with combustible materials.

Oxygen-enriched air: Cryogenic gases like liquid helium and liquid hydrogen are so cold that they can easily liquefy the air they come in contact with. For example, liquid air can condense on a surface cooled by liquid helium or hydrogen. Nitrogen evaporates more rapidly than oxygen from the liquid air. This action leaves behind a liquid air mixture which, when evaporated, gives a high concentration of oxygen. This oxygen-enriched air now presents all of the same hazards as oxygen.

Liquid oxygen hazard: Cryogenic liquid like liquid oxygen comprises 4,000 times more oxygen by volume than normal air. Materials that are usually considered non-combustible like stainless steels, carbon, aluminum, cast iron, zinc, PTFE can become flammable in the presence of liquid oxygen. There can be explosive reaction in organic materials if a flammable mixture is produced. Clothes soaked in liquid oxygen can remain highly flammable for hours.

Explosion due to rapid expansion: There is another drawback of cryogenic gases. When these gases are not stored properly or if there are no adequate venting or pressure-relief devices on the containers, enormous pressures can build up inside the containers. The pressure inside causes an explosion popularly called as BLEVE or boiling liquid expanding vapor explosion. It becomes difficult to handle this increased pressure and explosion occurs. Therefore, the containers for storing cryogenic gases must also have another backup device such as a bursting disc.

Over Pressurization: In cryogenic process, high pressures are formed by:

• compression of gases during refrigeration.
• pumping of liquids to high pressures.
• confinement of cryogenic fluids followed by evaporation.

• Can cause asphyxiation. This occurs when the air air necessary for the support of life is displayed.
• They cause frostbite, freezing burns, and destruction of tissue.
• They are extremely cold and their vapors can freeze human tissue.
• Boiling and splashing occurs when the cryogenic gases come in contact with warm objects.
• Cryogenic gases can make materials like plastic and rubber to become brittle and fracture under stress.
• Liquid to gas expansion ratio. Cryogenic gases can build up tremendous pressures in a closed system and so the dispensing areas need to be well ventilated.
• Cryogenic gases which are flammable causes serious fire and explosion hazards.