Liquid nitrogen safety is critical when using or storing liquid nitrogen (LN2). Due to its low temperature, LN2 is extremely dangerous if not handled correctly. This is why the Occupational Safety and Health Administration (OSHA) has developed a list of nitrogen safety requirements when working with this gas in its liquid state.
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 it 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 and for freezing materials.
What are the main hazards when working with liquid nitrogen?
Although liquid nitrogen is not toxic, it does have two major life threatening hazardous properties. Because liquid nitrogen can evaporate quickly, it can effectively displace air to create an atmosphere that is unable to support life. In addition, it can also cause severe injury due to the intense cold of the liquid.
Hazards when working with liquid nitrogen include:
- Extreme cold
- Asphyxiation
- Oxygen enrichment
- Pressure Buildup
- Liquid spills
- Rapid phase change
- Explosion
What is the expansion rate of LN to gas?
Liquid nitrogen expands 696 times in volume when it vaporizes. It has no warning properties such as odor or color. Thus, very small amounts of liquid nitrogen can create an oxygen deficient environment and drive the O2 level below OSHA's safe standard of 19.5%. Oxygen deficiency may cause severe health risks including nausea, dizziness, unconsciousness, and potentially, asphyxiation.
Understanding the hazards associated with the expansion rate of nitrogen is crucial to prevent accidents and ensure worker safety. The primary hazard related to the expansion rate of nitrogen is associated with rapid pressure changes that can occur when nitrogen is released from a high-pressure vessel or when there is a sudden release of compressed nitrogen gas.
By following proper nitrogen safety protocols and being aware of the hazards associated with the expansion rate of nitrogen, workers can minimize the risks associated with handling this gas in various industrial settings.
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 1:696. 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?
Technically, no. Nitrogen is a common gas found in nature. However, when stored under pressure in sealed containers or in its liquid state there are two primary dangers. The first is asphyxiation. Because of its rapid expansion, it can quickly displace oxygen in an enclosed area. The second is the result of its cold temperatures. It will immediately freeze exposed skin.
Can you dip your bare hands into a container of liquid nitrogen?
The short answer is no, you should not dip your hands into any container of liquid nitrogen. Liquid nitrogen is extremely cold, with a boiling point of -196°C (-321°F) at atmospheric pressure. Any skin contact with liquid nitrogen can cause severe frostbite or thermal burns due to the rapid freezing of tissues. For those that even encounter brief exposure to liquid nitrogen this can result in severe injury.
When liquid nitrogen comes into contact with skin, it immediately evaporates, creating a layer of gas around the skin. However, this gas layer can quickly dissipate, allowing direct contact between the liquid nitrogen and the skin, leading to rapid freezing and damage.
This is why using personal protective equipment (PPE) such as insulated gloves and goggles, should be worn when handling liquid nitrogen. Additionally, it's essential to follow appropriate safety protocols and receive proper training before working with cryogenic substances and understanding gas detection safety monitors to prevent accidents from occurring.
How long does liquid nitrogen take to evaporate?
Liquid nitrogen has a very low boiling point and can evaporate very quickly, causing it to expand. When it comes to the evaporation rate it depends on several factors:
Temperature and pressure
At room temperature (20°C), liquid nitrogen has an evaporation rate of approximately 0.2 liters per hour for any open container.
Container insulation
A well-insulated cylinder of liquid nitrogen can take several days to evaporate if open to the air.
Surface area-to-volume ratio
The rate at which liquid nitrogen levels fall is determined by the exposed surface area-to-volume ratio.
Substrate thermal conductivity and specific heat
Liquid nitrogen takes longer to evaporate on a polystyrene surface than on a metal surface.
Substrate surface
The rate of evaporation is also influenced by how much the liquid nitrogen is allowed to spread on the substrate.
What are the ventilation requirements for liquid nitrogen?
In order to prevent oxygen deficiency from occurring, areas where nitrogen is used or stored require sufficient ventilation. These ventilation requirements are typically established by regulatory bodies, industry organizations, and relevant authorities. These could include but are not limited to, Occupational Safety and Health Administration (OSHA), National Fire Protection Association (NFPA), and American National Standards Institute (ANSI) to name a few.
The ventilation requirement consensus typically states that at least four to six changes of fresh air are needed per hour and should be provided. This does depend however, on room size, the quantity of nitrogen being used and the presence of an oxygen gas detection monitoring system.
What are the safety rules for Liquid Nitrogen?
1. Do not inhale liquid nitrogen
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.
2. Wear appropriate personal protective equipment (PPE)
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.
3. Never consume liquid nitrogen directly
Liquid nitrogen as a liquid has a very low boiling point of -196°C and accidental ingestion could cause asphyxiation and airway or gastric perforations due to the extreme cold temperature. You could also take the risk of severely burning your mouth and esophagus.
4. Use liquid nitrogen in well-ventilated areas
You should always ensure you are using liquid nitrogen in well-ventilated areas and never dispose of it by pouring on the floor or pavement. By using liquid nitrogen in a confined or enclosed space you could displace enough oxygen to cause asphyxiation or suffocation.
5. Only use containers and equipment designed for cryogenic service
By using containers such as dewars, you can ensure that the contents stay in cryogenic state and guarantee safety in operations such as storing or transporting gases.
What hazmat class is liquid nitrogen?
Liquid nitrogen is actually not assigned a Hazardous Materials (Hazmat) class according to traditional classification systems like those used by the U.S. Department of Transportation (DOT) or the United Nations. Instead, it's typically classified as a cryogenic liquid.
However, despite not being assigned a Hazmat class, liquid nitrogen is still considered hazardous due to its extremely low temperature and potential for causing frostbite or severe burns upon contact with skin or other materials. It can also displace oxygen in confined spaces, presenting fatality or asphyxiation hazard.
Its vital to follow safety protocols and guidelines specific to cryogenic liquids to mitigate risks and ensure safe handling practices. This includes using appropriate personal protective equipment, implementing proper ventilation, and adhering to storage and handling procedures designed to prevent injury in the workplace.
