LABOplus - Arbeitsschutz in Tiefstkälte - Safety at Work Risks

Risks

The following instructions shall be respected while working with liquid nitrogen.Tominimise the risk of accidents and their consequences a few precautions should be taken, particularly related to:

CRYOgenic burns
Oxygen deficiency
Oxygen enrichment
Risks of explosion

CRYOgenic burns

Liquid nitrogen is deep cold (-196°C).

Parts of vessels that have been in contact with liquid nitrogen, especially while refilling, can burn the skin in case of direct contact.

Danger

CRYOgenic fluids can:

  • cause burns on the skin
  • make materials (metallic or plastic) brittle in case they are not suitable for ultra-low temperatures
  • cause strong nebulosity, depending on the air humidity of premise

Causes

There are two kinds of cryogenic burns:

Burns by splashes
It is important to protect yourself against the risk of splashes while using liquid nitrogen, especially when handling with samples. Splashes can cause cryogenic burns that can have serious consequences, especially when hitting eyes or face and skin.

Contact burns
Contact between skin and cold materials causes frostbites or cryogenic burns.
Never touch or grip the inner side of cryogenic vessels or samples with a bare hand.

Recommendation

Proceed as follows to prevent the risks of burns:
  • prevent skin contact with cryogenic liquids
  • never touch the cold walls of vessels, or un-insulated or frosted equipment
  • wear individual protection equipment (suitable gloves CRYO GLOVES, protective visors (faceshield) and closed shoes)
  • always hold the vessel in the vertical position
  • use only suitable equipment (metal or PTFE hose) for refilling the container
  • train personnel

Note, this list is not complete…

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Oxygen deficiency

The approximate composition of air by volume is as follows for its main components:

Oxygen O2 21%
Nitrogen N2 78%
Argon Ar 1%

This gases are not toxic, but changes in their relative constituents, and particularly oxygen, have an effect on life and combustion processes. Therefore it is essential that the air we breathe should contain sufficient oxygen (> 19%).
Our senses are incapable of detecting changes in the concentration of the constituents of air sufficiently quickly, since they are odourless and colourless.

Danger

The risk of suffocation is high due to normal evaporation of liquid nitrogen to nitrogen gas that displaces oxygen in the inhaled air. For example, under standard temperature and pressure conditions (20°C; 1013 mbar), 1 liter of liquid nitrogen evaporates to 680 liters of nitrogen gas. The critical limit of oxygen can be easily reached.
Oxygen deficiency is dangerous and can cause death from suffocation.
The reaction of the organism to oxygen deficiency is different from one person to another.
It is impossible to give any valid information in general about symptoms of a starting oxygen deficiency.

Causes

To protect yourself from risks of oxygen deficiency pay attention to following points:

  • usage of liquid or gaseous nitrogen
  • natural evaporation of liquid nitrogen
  • refilling of liquid nitrogen
  • leaks in storage tanks for liquid or gaseous nitrogen
  • defective vent pipes or exhaust pipes
  • tipping over the vessel

Note, this list is not complete…

Protective Action

Proceed as follows to prevent the risks of oxygen deficiency:

  • keep always the vessel in the vertical position
  • close the vessel with an suitable lid
  • do not put the vessel in bright sunshine or close to a heat source
  • do not transport the vessel by car
  • premises must always be well ventilated
  • prevent strokes, avoid shocks and sudden movements
  • wear always individual protective equipment (suitable gloves CRYO GLOVES, protective faceshield and closed shoes)
  • check the oxygen content continuously and carry an oxygen meter (portable gasmonitor GasAlertClip Extreme)
  • train and instruct personnel

Note, this list is not complete…

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Oxygen enrichment

Danger

Oxygen enrichment can enlarge the risk of explosion or fire.

Causes

Oxygen enrichment, as a result of liquefaction of ambient air, can occur, because the boiling point of oxygen is higher (-183°C) than the boiling point of liquid nitrogen (-196°C).

Protective Action

Proceed as follows to prevent the risk of explosion in case of oxygen enrichment:

  • do not smoke
  • eliminate easily inflammable products from the area of vessel, if possible
  • eliminate all sources of fire (flames, sparks, matches, lighters, etc.)
  • premise of vessel must be continuously and adequate ventilated
  • clean the floor regularly
  • train personnel
  • wear individual protection equipment (suitable gloves CRYO GLOVES, protective faceshield and closed shoes)
  • check the oxygen content continuously and always wear an oxygen meter (portable gasmonitor GasAlertClip Extreme)

Note, this list is not complete…

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Risks of explosion

Danger

The evaporation of liquid nitrogen can cause an overpressure inside of the vessels.

Causes

The increase of pressure in the vessel may happen due to:

  • poor maintenance of the container
  • accumulation of ice on the neck and the lid

Protective Action

Proceed as follows to prevent the risks of explosion:

  • always use a suitable lid (pay attention to an exhaust gas opening)
  • respect filling levels to prevent the formation of ice on the lid
  • use the vessel only in dry and sheltered locations
  • control the humidity of the room
  • check vessel periodically with regards to accumulations of condensation water
  • check vessel periodically with regards to surface defects and material damages

Note, this list is not complete…

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