Nitrogen is the most common gas in the earth’s atmosphere. Approximately 78 percent of the air you breathe is nitrogen. In its liquid form, nitrogen is used in many industries. However, because liquid nitrogen is potentially dangerous if not handled correctly, the Occupational Safety and Health Administration OSHA has developed a list of safety requirements when working with this gas.
What is liquid nitrogen?
Nitrogen gas is inert, meaning it does not form chemical compounds with other molecules. It is odorless, colorless, and tasteless. This makes it safe to add nitrogen to food or for industrial processes. In addition, Nitrogen, in its liquid form, is easy to transport in tanks or cylinders.
But its most useful property is that liquid nitrogen is cold. Liquid nitrogen has a boiling point of -320°F (-196°C). At any temperature above this is becomes a gas. By piping LN (liquid nitrogen) around or into other gases or objects, it can be used to cool them. This makes it useful as both a coolant or for freezing materials.
What is liquid nitrogen used for?
The ability to freeze or quickly cool water, living tissue or other materials has made LN important in many processes that require extreme cooling or freezing. For example, doctors use it for cryosurgery to remove skin lesions or moles. It is used for the storage and transportation of blood, body parts, and foods. Bottlers use it to remove oxygen from the headspace of bottles before capping. Scientists us it for cooling in experiments or to cool CCD cameras for astronomy. It is used in industry to temporarily shrink metal parts for precision fitting. It is used to freeze scrap rubber and plastic so it can be efficiently ground for recycling.
Is liquid nitrogen flammable?
Liquid nitrogen – like nitrogen gas - is not flammable. However, as liquid nitrogen is exposed to normal temperatures and becomes a gas it expands at a rate of 1:694. This has given rise to the idea that LN can cause an explosion. While technically not true, a rapid expansion of the liquid to gas as a result of a leak or a fire surrounding the LN container or transport pipes can create extremely dangerous pressures resulting in an non-flammable explosion of the container.
Is liquid nitrogen dangerous?
There are two primary dangers from liquid nitrogen. The first is asphyxiation. Because of its rapid expansion, it can displace oxygen in an enclosed area. The second is the result of its cold temperatures. It will immediately freeze exposed skin.
Liquid Nitrogen Safety
Liquid nitrogen inhalation
Asphyxiation is the primary risk. A person exposed to high levels of nitrogen gas should be removed from the source of the gas and administered rescue breathing if required. Rescuers or people working in enclosed areas with the potential of LN exposure should wear a self-contained breathing apparatus.
Liquid nitrogen exposure
Proper handling. storage, and use of LN is critical to worker safety. Liquid nitrogen can cause burns equivalent to frostbite. Therefore, a positive pressure, full face, air supplied breathing apparatus should be used when working with LN in confined spaces. A face shield that protects the eyes and face should be used to protect from splashes. Insulated gloves, aprons and footwear covering designed for the handling of cryogenic gases should be worn to minimize contact with accidental splashes.
Liquid nitrogen toxicity
LN is non-toxic.
Liquid nitrogen flammability
LN is non-flammable.
Liquid nitrogen safety OSHA
The occupation Safety Health Administration OSHA Standards number 1910.101, 1910.1200 and 1910.1450 sets the standards for workplace safety for anyone working around LN or other cryogenic gases. Employers or employees should refer to both this OSHA Quick Fact Sheet as well as this published interpretation of the standard for the most current OSHA information.
While there is no standard OSHA signage for LN many safety sign companies offer yellow caution signage with the text "CAUTION - Liquid Nitrogen - Gloves and Face Shield Required".
Liquid nitrogen Material Safety Data Sheet
Linde, a supplier of liquid gases in the US, has this material data safety sheet available for download (pdf)
Liquid nitrogen NFPA Rating
The National Fire Protection Association NFPA 704 Rating diamond for liquid nitrogen is
- 0 (no hazard) health
- 0 (will not burn) flammability
- 0 (stable) toxicity
- blank for specific hazards.
Liquid Nitrogen Safety Alarms
The danger of asphyxiation in enclosed areas when liquid nitrogen or any cryogenic gas is stored or utilized can be minimized by installing oxygen depletion safety alarms. The oxygen depletion alarms are designed to measure and alarm before the oxygen concentration in an enclosed space is dangerous to human life. By installing these devices you can provide employee’s adequate warning before entering an enclosed area where the oxygen level may have dropped below the OSHA standard of 19.5%.
For example the Remote Oxygen Depletion Safety Alarm is designed to protect employees and customers near stored inert gases like cylinders of nitrogen, argon, or helium. It meets all OSHA requirements for safety.
The Oxygen Deficiency Alarm for Low Temperature has the same features, meets all the same OSHA requirements, and is designed to be used in refrigerators or freezers down to -50ºC.
The RAD-0002-ZR utilizes a zirconium dioxide oxygen sensor allowing it to measure oxygen concentrations at extremely low temperatures. The inclusion of this new sensor allows the RAD-0002-ZR to be installed in applications requiring safety monitoring in those extremely low temperatures like food and cryogenic storage.