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 liquid nitrogen 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.
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
- Container insulation
- Surface area-to-volume ratio
- Substrate thermal conductivity and specific heat
- Substrate surface
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.
What is the OSHA exposure limit for liquid nitrogen?
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". It is also recommended to install signage outside dangerous areas noting, "Warning - Oxygen Deficient Confined Space".
For more safety resources on liquid nitrogen, download the USDA guide here.
Can you use liquid nitrogen to freeze dry food?
One of the most popular industries for liquid nitrogen, is food freezing. Food grade liquid nitrogen holds many advantages over mechanical freezing or chilling processes. In fact, using liquid nitrogen is faster, more flexible, and takes up less space. When it comes to food quality, liquid nitrogen can help food products maintain their moisture, preventing loss from hydration and create greater flavors.
In addition, liquid nitrogen can be used to preserve food and protect the nutrients, because oxygen can oxidize the food material and ingredients. In some environments, liquid is even used to modify the atmosphere of packaging and ensure the products remain safe and high quality for the end customer.
Benefits of Liquid Nitrogen for Food Freezing?
Liquid nitrogen is commonly used in the food industry and offers many benefits, quickly becoming the 'go to' coolant to freeze and powder products that were unimaginable a while back. A few benefits that liquid nitrogen provides include:
- Rapid Freezing: Liquid nitrogen has an extremely low temperature of around -320°F (-196°C). This allows for rapid freezing of food products, minimizing the formation of ice crystals and preserving the quality of the food.
- Preservation of Texture and Nutrients: The quick freezing process with liquid nitrogen helps maintain the texture, color, and nutritional content of the food. This is especially important for delicate items like fruits, vegetables, and seafood.
- Extended Shelf Life: By preventing the growth of microorganisms and enzymes, liquid nitrogen freezing helps extend the shelf life of food products. This is crucial for preserving perishable items and reducing food waste.
- Improved Product Quality: The fast freezing process with liquid nitrogen results in smaller ice crystals, which reduces cell damage in the food. This contributes to better texture and taste when the food is thawed and prepared.
- Flexible Packaging Options: Liquid nitrogen freezing allows for a variety of packaging options, including individually quick frozen (IQF) items. This enables manufacturers to package and store food in convenient portions, providing flexibility for both producers and consumers.
- Energy Efficiency: Liquid nitrogen freezing systems are often more energy-efficient than traditional methods. The quick freezing reduces the overall processing time, leading to energy savings in the long run.
- Customization of Freezing Conditions: Liquid nitrogen freezing systems offer control over the freezing process, allowing manufacturers to tailor the conditions based on the specific requirements of different food products.
- Reduced Ice Crystal Formation: The rapid freezing with liquid nitrogen minimizes the formation of large ice crystals, which can negatively impact the quality of frozen foods. This is particularly beneficial for items like ice cream and frozen desserts.
- Safe Handling: Liquid nitrogen is inert and doesn't introduce any unwanted flavors or chemicals to the food. Proper handling and storage precautions are necessary due to its extremely low temperature, but when used correctly, it is considered safe for food applications.
Overall, liquid nitrogen freezing provides a technologically advanced and efficient method for preserving the quality, increasing freshness and extending the shelf life across a wide range of food products. However, within this application oxygen safety monitors should be utilized to prevent potential hazards from occurring. The CM-902-S is an industrial oxygen deficiency safety alarm specifically designed to meet FDA requirements around food production applications.
Storage and Ventilation Guidelines for Liquid Nitrogen
Storing liquid nitrogen safely requires more than just a secure container, it demands a well-ventilated area that can prevent oxygen displacement and pressure buildup. Because liquid nitrogen rapidly expands into gas (at a ratio of 1:694) as it warms, even small leaks in an unventilated space can quickly create an oxygen-deficient atmosphere.
It's important to always use containers specifically designed to handle extreme cold and pressure and ensure they are kept upright and secured to prevent tipping or accidental spills.
In order to also 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 regulatory bodies 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.
Oxygen deficiency monitors are strongly recommended to alert personnel if oxygen levels drop below safe thresholds. It's also important to shore LN2 away from direct sunlight, heat sources, or combustible materials to reduce the risk of rapid pressure changes or container failure.
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 Placard
The National Fire Protection Association NFPA 704 Rating diamond placard for liquid nitrogen is
- 0 (no hazard) health
- 0 (will not burn) flammability
- 0 (stable) toxicity
- blank for specific hazards.
OSHA Oxygen Deficiency Signage
The Occupational Safety and Health Administration (OSHA) does not have a standardized sign specifically for oxygen deficiency. However, it does require employers to provide signage or warning labels in those areas where oxygen deficiency may be a concern.
In such situations, warning labels are required to:
- Inform individuals of potential hazard locations
- State specifics for "Danger of Oxygen Deficient Atmospheres"
- State specifics for "Low Oxygen Levels"
- Additionally, signs must specific symbols indicated proper safety monitoring equipment or respiratory protection
Liquid Nitrogen Uses in the Industry
The ability to freeze or quickly cool water, living tissue or other materials has also made liquid nitrogen important in many processes that require extreme cooling and freezing. For example such as:
- 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.
- Food producers use it in packaging to remove oxygen and prevent oxidization of the product
- 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.
Nitrogen Gas Safety Alarms
In the presence of nitrogen we measure the lack of oxygen instead of the specific nitrogen molecules. We choose to measure oxygen for two reasons: the nitrogen molecule is difficult to detect accurately (you'd need a mass spectrometer to be precise), and because our atmosphere is 78% nitrogen any change would be difficult to detect.
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 Oxygen Deficiency Alarm for Low Temperatures 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.
For those industries that are using liquid nitrogen in frozen food applications or industrial settings, implementing a industrial gas safety monitoring system, like the CM-902 Industrial O2 Gas Detector is ideal. This device meets the stringent codes of both OSHA and the FDA, including a industrial stainless steel enclosure to meet sanitation requirements.
The CM-902 utilizes a zirconium dioxide oxygen sensor, allowing it measure oxygen deficient environments at extremely low temperatures (down to -50ºC). It's design was created in order to protect individuals and employees working near gases like nitrogen, argon, propane, or helium in confined spaces. The device also is specifically suited for wash-down applications due to its durable enclosure.
Oxygen Deficiency Safety
For those working in and out of hazardous environments where liquid nitrogen is stored, used, or produced an oxygen deficiency or enrichment safety monitor is critical. These devices are designed primarily for enclosed areas where oxygen depletion or enrichment may cause personal harm. The monitor works by use of audible and visual alarms that indicate to personnel should oxygen levels drop below OSHA compressed gas standards. In addition, this safety alarm also can be used in walk-in refrigerators or freezers with temperatures as low as -50°C.
Compressed Gas Association LN Safety Resources
At CO2Meter, we pride ourselves on providing education and training resources on gas detection and what to do in the event of a potential hazard.
We work alongside many reputable associations like the Compressed Gas Association (CGA). The CGA remains dedicated to providing safety standards and safe practices for the industry and CO2Meter ensures that our devices meet these criteria for our partners across the globe.
Currently, the Compressed Gas Association is in the works to create a standard specifically for oxygen safety monitoring in food freezing applications in response to the poultry facility incident in Gainesville, GA.
Below you will find just a few of their most current Liquid Nitrogen CGA code standards:
- CGA P-76, Hazards of Oxygen-Deficient Atmospheres
- CGA SA-29, Safety Alert, Hazards of Liquid Nitrogen in Near-Consumer Applications
- CGA TM-3, eLearning: Safe Handling of Cryogenic Liquids in Portable Containers
- CGA P-12, Safe Handling of Cryogenic Liquids
- CGA P-9, The Inert Gases: Argon, Nitrogen, and Helium
In addition, here are a few additional safety posters in for the "Safe Use of Liquid Nitrogen" and "Liquid Nitrogen in Cryogenic Environments" from the CGA as a free safety resource to share regarding codes, regulations, and industry standards.
For more information on Liquid Nitrogen safety, gas detection safety alarms, or meeting standards you can speak to a CO2Meter specialist at Sales@CO2Meter.com or call us directly at 877-678-4259.
