Asphyxiation with liquid nitrogen - hazard alert

November 2003

The increased use of liquid nitrogen in biomedical research in recent years has unfortunately resulted in two fatal incidents in research institutions in Australia and the UK. Some recent incidents that occurred this year at Monash University have highlighted the need for all departments/schools/centres that use liquid nitrogen to review their usage, storage and safety management systems.

1. What are the hazards associated with liquid nitrogen?

Liquid nitrogen is a cryogenic liquid and the hazards associated with it arise from either its very low temperature, the nature of the gas evolved when it boils or a combination of these as detailed below.

Characteristics of liquid nitrogenAssociated Hazards
1. Absence of warning properties
  • It is a colourless liquid
  • As it boils it generates gaseous nitrogen which people cannot detect
  • It is also an asphyxiant, as it cannot support life
Asphyxiation - People cannot detect nitrogen in the air as it is
  • non-flammable & non-toxic
  • colourless, odourless & tasteless
So there is no warning if the atmosphere has become oxygen deficient.
2. Large expansion ratio on evaporation
  • 1 litre of liquid nitrogen → 682 litres of gas
Asphyxiation - Only a relatively small volume of liquid nitrogen has to evaporate within a room to result in an oxygen deficient atmosphere.
Pressure build up &/or explosion - Pressure can build up in a sealed container due to the boil off of nitrogen gas. An explosion can occur if the container is not rated to withstand the pressure.
3. Low temperature
  • Temperature of -196 °C or below at atmospheric pressure
  • The boiling point of liquid nitrogen is higher than that of liquid oxygen so it can condense liquid oxygen from the atmosphere
Cold burns and frostbite - Cold burns or frostbite can result from direct contact with the liquid. (Note: Storage &/or evaporation of very large volumes of liquid could drop the local atmospheric temperature low enough to cause frostbite or hypothermia. This type of incident is unlikely at Monash )
Increased risk of splashes caused by temperature differentials - There is a high risk of jets or spurts of liquid nitrogen occurring when items, at much higher temperatures than -196 °C, are placed in liquid nitrogen. Pockets of nitrogen gas are formed below the surface of the liquid and can rise rapidly, carrying a jet of liquid with them.
Fire/explosion in an oxygen enriched atmosphere - An oxygen rich atmosphere can result from either condensation or evaporation of liquid oxygen. An oxygen rich atmosphere increases the risk of fire. An explosion may even occur if the evaporation of the liquid oxygen occurs in the presence of organic material (eg cold traps on vacuum lines).

2. Incidents involving liquid nitrogen

These examples highlight the need for all departments/schools/centres to ensure that they have safe systems in place for the use, storage and management of liquid nitrogen.

2.1 Monash University

i. Incident in February 2003

What happened?

  • A large volume of liquid nitrogen spilt in a small non-ventilated cool room as a tap on a pressurised decanting vessel was left on
  • Evaporation of the liquid produced nitrogen gas that reduced the oxygen level to 5% and the alarm sounded. Note: if a person had entered the room at this time they would have been dead within minutes

How was the incident managed?

  • A low oxygen detection alarm system had been installed
  • A staff member responded to the alarm, knew what the alarm was, knew that it was not safe to enter room and implemented emergency procedures

ii. Incident in July 2003

What happened?

  • A laboratory support room contained a liquid nitrogen sample storage container for the preservation of biological samples
  • The sample storage container was refilled directly from a transportable 160L pressurised vessel, which normally takes between 10 to 20 minutes
  • To decant, a tap is turned on and the decanting continues until the tap is manually turned off
  • The room was left unattended during decanting with staff checking the status at regular intervals. Another staff member, who was planning to enter the room, found liquid nitrogen spilling over the edges of the storage vessel onto the floor

How was the incident managed?

  • The person who found the spill did not enter the room
  • Assistance was summoned from other staff working in the area
  • A documented emergency procedure was not readily available
  • A senior staff member was informed and implemented ad-hoc procedures to manage the situation
  • The room was then ventilated until safe to enter

2.2 Other research facilities - recent fatalities

iii Fatality in Australia in 2001

In December 2001, a staff member at Australian Animal Health Laboratories in Geelong died after entering a room filled with nitrogen gas. The room was used for the storage of samples in cabinets containing liquid nitrogen. Under normal operation, the gas produced by liquid nitrogen evaporation is removed from the room by an exhaust ventilation system. The ventilation system failed due to a series of failures of the laboratory's complex engineering and control systems and the room filled with nitrogen gas. These failures, coupled with inadequacies in relation to staff being alerted to, and understanding the seriousness of, the failures led to the tragedy.

iv. Fatality in research facility in the UK in 1999

In 1999, a fatality involving use of liquid nitrogen occurred at the Human Genetics Unit, located at the Western General Hospital in Edinburgh. Four other people were also injured during this incident. An experienced laboratory worker, who had worked with liquid nitrogen over a period of years, died whilst filling flasks with liquid nitrogen. Seven hundred litres leaked into the laboratory and evaporated, asphyxiating him. A colleague, who entered the room to investigate a hissing noise, which was due to liquid nitrogen streaming from a hose attached to the wall, was able to turn off the supply and summon help before she too was overcome. Three other people were injured during this incident

3. Actions to be taken at Monash University

  • A task force on safety management of liquid nitrogen and other cryogenic liquids has been established within OHSE
  • This hazard alert will be distributed to promote awareness of this serious hazard
  • A survey of the use, storage and management of liquid nitrogen and other cryogenic liquids is in progress to identify common issues across the University. OHSE consultants will provide departments/schools/centres with survey sheets (hard and soft copies vailable) to assist in the review of their safety management systems for the use and storage of liquid nitrogen and other cryogenic liquids
  • Departments/schools/centres are to return the completed survey sheets to OHSE
  • OHSE will review the responses and identify appropriate recommendations and implementation strategies to reduce the risk of incidents involving liquid nitrogen and other cryogenic liquids

Further information

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