Liquid Nitrogen Safety
Cryogenic liquids are liquefied gases having boiling points of less than -73.3C (-100F). Some hazards of cryogenic liquids include both physical hazards such as fire, explosion, and pressure buildup and health hazards such as severe frostbite and asphyxiation. Potential fire or explosion hazards exist because cryogenic liquids are capable, under the right conditions, of condensing oxygen from the atmosphere. This oxygen-rich environment in combination with flammable/combustible materials and an ignition source are particularly hazardous.
Pressure is also a hazard because of the large volume expansion ratio from liquid to gas that a cryogen exhibits as it warms and the liquid evaporates. This expansion ratio also makes cryogenic liquids more prone to splash and therefore skin and eye contact is more likely to occur. Contact with living tissue can cause frostbite or thermal burns, and prolonged contact can cause blood clots that have very serious consequences. All laboratory personnel should follow prudent safety practices when handling and storing cryogenic liquids.
Of these hazards oxygen deficiency hazard (ODH) is one of the most significant hazards with storage and use of cryogenic liquids.
Factors that could lead to ODH include:
- Equipment failure (container, lab equipment)
- Piping failure (transporting LN2 to equipment)
- Human error (leaving valves open)
- Inadequate Ventilation or Ventilation failure
Normally air is comprised of nitrogen (78.08%), oxygen (20.95%), argon (0.93%) and carbon dioxide (0.13%), with the remainder being a mixture of gases. An oxygen deficient atmosphere is “an atmosphere containing less than 19.5% oxygen by volume”. Oxygen deficient atmospheres could cause asphyxia in two ways: sudden and gradual. Humans vary considerably in their reaction to oxygen-deficient atmospheres and it is not possible to predict exactly how they will react. However, a general indication of what could happen is listed below:
- Sudden and acute asphyxia would occur from the inhalation of little to no oxygen. Unconsciousness without warning would be immediate upon one breath of oxygen concentrations at levels below 10% to the point that the person could not evacuate or use an air-line respirator or SCBA. At levels below 16%, impaired perception and judgment, fatigue, and poor muscular coordination would impede self-rescue due to being wholly unaware that anything is wrong. Sudden asphyxia could occur with a large release of LN2 or if someone entered a room when the oxygen is depleted.
- Gradual asphyxia can occur at any level below 20.9%, which is normal oxygen content. Symptoms of hypoxia (i.e., reduced oxygen to tissue), such as accelerated breathing and heart rate, increase at levels closer to 17%, although these symptoms may vary with individuals. A feeling of euphoria can set in during hypoxia, making the victim unaware of the danger and thus making no attempt to self-rescue. Gradual asphyxia could occur during an increased use of nitrogen, gaseous or liquid, as cylinders normally relieve pressure, or if valves or fittings freeze and stick open.
Because cryogenic liquids have the potential to create an oxygen deficient atmosphere when released if not properly managed and controlled. The following must be considered when cryogenic liquids are stored or used:
Safety in our laboratories is a top priority for Indiana University. We store and utilize liquid nitrogen in many of our laboratories and ask that you contact your campus EHS office with any questions regarding the use of cryogenic liquids as they can pose a significant risk when released, leading to oxygen deficient hazards if not properly managed and controlled.