Health hazards of cyrogenic gases
- 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.
Several types of situations exist that may result in a flammability hazard
including:
- 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.
If this confined fluid is released all of a sudden, a significant
thrust is experienced. Over-pressurization of cryogenic gas occurs when
during the phase of change from liquid to gas is not vented properly.
The vaporization of cryogenic fluids produce large volumes of gas. A
container with inadequate pressure relief will lead to accumulation of
pressure till the container ruptures, which leads to serious injury.
- Materials and construction hazards: Another drawback of
cryogenic gases is that with very low temperatures, the selection of
materials requires the knowledge of the effect of the temperatures on
the properties of those materials. For example, there are metals which
become brittle at low temperatures, which can result in material
failure. Low temperature product can also fail on account of thermal
stresses. There are some materials which shrink when extremely cold,
thereby leading to additional stress and can also result in leaks.
A quick recap
Hazards of cryogenic gases/liquids:
- 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.
|
What
is Cryogenic Gas
Cryogenic
Gas Hazards