The image of liquid nitrogen has been glamorized recently in TV cookery programs by chefs such as Heston Blumenthal. However, whether you are going to use it to make homemade ice cream or to snap-freeze samples in the lab, liquid nitrogen safety is critical, as this reagent is not something to fool around with.
In this article, we highlight the dangers of liquid nitrogen, the necessity of appropriate liquid nitrogen safety training and share our top tips for avoiding liquid nitrogen dangers in the lab.
Liquid Nitrogen Safety: Why is it Important in the Lab?
Liquid nitrogen, (also referred to as LN2) is a cryogenic liquid commonly used in labs. In biology research settings its primary use is for preserving biological materials such as tissue samples and cells. This is a critical application in many research settings, which means if you work in a biology lab you are probably going to have to handle liquid nitrogen at some point.
Unfortunately, researchers have had life-changing injuries and even lost their lives because of accidents involving liquid nitrogen making it critical that only working with this liquid fully appreciates the dangers. (1,2)
Liquid Nitrogen Dangers
- It’s Extremely Cold
The boiling point of liquid nitrogen is -196ºC and it freezes at -210ºC. Between these values, liquid nitrogen is in the liquid state. The extreme cold of this liquid means that contact with bare skin can result in cold burns, cell damage, and life-changing injuries such as retinal detachment in a person’s eye. Liquid nitrogen can also cause common materials such as plastic, carbon steel, and rubber to fatigue and eventually fracture.
- It’s an Asphyxiant
One of the most dangerous properties of liquid nitrogen is its capability to vaporize into a large volume of gas. The liquid-to-gas expansion ratio is 1:694 at 20ºC, meaning that just 1 L of liquid nitrogen can expand to 694 L of gas. (3) If enough liquid vaporizes in a confined space, the air can be displaced resulting in an oxygen deficiency.
The reduced oxygen concentration can quickly result in feeling dizzy and render you unconscious with little warning, as nitrogen gas is colorless, odorless and tasteless.
This is why areas where liquid nitrogen is stored and handled should have appropriate oxygen sensors that alarm when the oxygen concentration falls.
- It Can Cause Explosions
The large expansion ratio also means that if liquid nitrogen vaporizes in a confined space with no escape, the pressure buildup can result in an explosion. Therefore, liquid nitrogen storage equipment should have appropriate pressure-relief devices.
Now you know the dangers of liquid nitrogen let’s look at how you can handle it safely in the lab.
Top Tips for Safety Handling Liquid Nitrogen
1. Get Proper Liquid Nitrogen Safety Training
Before you start work with liquid nitrogen in the lab, whether it is using a dewar flask for flash-freezing or placing your cells in for cryo-storage, you need to get proper safety training.
Speak to your supervisor or lab safety manager – they should provide appropriate training, including on PPE, safe handling, and what to do in an emergency.
The potential dangers of liquid nitrogen mean that you should get some basic safety training if it is being used in the same area you work in, even if you aren’t directly working with it.
2. Know How to Store and Transport Liquid Nitrogen
The storage of liquid nitrogen containers is highly regulated. There are specific health and safety requirements that require good ventilation and limit the number of storage containers in one room. Make sure you are familiar with your institute’s policies.
When aliquoting a smaller amount for use in a laboratory procedure, only use a container specified for liquid nitrogen. Do not use a domestic vacuum flask or any old container hanging around the lab. Un-insulated containers can freeze to skin and tear it when removed. Unsuitable containers can also suddenly crack and spill liquid nitrogen everywhere.
3. Wear Appropriate Personal Protective Equipment
When using liquid nitrogen, you want to protect your skin, particularly your face, and also your eyes, from splashes. Therefore, you need to wear personal protective equipment (PPE) including a lab coat, specialized gloves and googles. Note that depending on the type of gloves you use, you may only be protected from the extremely low temperatures of stored items, not from direct exposure to liquid nitrogen, so don’t submerge your hands.
While small splashes of liquid nitrogen may not cause a burn, thanks to the leidenfrost effect, (3) if allowed to pool liquid nitrogen can cause severe burns.
For added protection, you should also consider wearing goggles under a full-face shield. I personally got splashed in the eye when organizing cryotubes in a Dewar, despite having a full-face shield. The stuff can shoot up from all angles!
Also, you should ensure that your footwear doesn’t leave any exposed areas, else you could end up with frostbitten feet.
4. Work in a Well-Ventilated Area and Avoid Confined Spaces
As we discussed in the above section on liquid nitrogen dangers, asphyxiation is a real risk. Ensure any area you are working in with liquid nitrogen is well-ventilated, avoid confined spaces such as elevators and monitor oxygen levels.
If this can’t be avoided, speak to your lab safety manager on necessary steps to ensure that risks are appropriately managed, such as not allowing others to ride in the elevator and ensuring a colleague is aware.
5. Do Not Work with Liquid Nitrogen when You are Alone in the Lab or After Hours
When working with liquid nitrogen, particularly when dispensing from a large to a small container, make sure a colleague is nearby and is aware of what you are doing. The importance of this is highlighted by the tragic death of a researcher working alone. (2)
6. Use Only the Necessary Amount of Liquid Nitrogen
The large expansion volume of liquid nitrogen means that you should limit the amount you are using and handling to the minimum you need. Using excessive amounts can dramatically increase the risk of asphyxiation.
7. Don’t Go Diving into a Storage Container to Retrieve a Dropped Sample
No sample is worth asphyxiating yourself from the vapors or burning your face and/or hands when the liquid bubbles up.
8. Never Use Liquid Nitrogen in a Closed Container
Liquid nitrogen boils rapidly and can cause ice dams to form or pressure to build up, resulting in explosions. Make sure storage containers are properly vented and never use liquid nitrogen in a closed system.
9. Never Put Liquid Nitrogen Down the Sink
It can cause the pipes to crack and you will end up with an expensive repair bill. Furthermore, liquid nitrogen poured down one drain can come up another, which could be a nasty surprise for a colleague in the lab next door.
10. Watch Out for Exploding Cryotubes
Cryotubes should be safe for liquid nitrogen, right? Not always. Liquid nitrogen can unknowingly enter cryotubes through minute cracks and then expand quickly when the tube thaws. An exploding cryotube can be like a mini-missile and a former colleague of mine has a mark on her forehead to prove it!
Liquid Nitrogen Safety in the Lab Summarized
Liquid nitrogen safety is important when working in the lab. If you or others in your lab are working with liquid nitrogen, ensure you have the appropriate liquid nitrogen safety training.
Some key considerations to avoid the potential dangers of liquid nitrogen include, work in a well-ventilated area and monitor oxygen levels if working with large amounts. Never work with liquid nitrogen alone or out of hours in case of emergencies. Wear appropriate PPE to minimize the risk of cold burns and other liquid nitrogen-related injuries. Use appropriate storage containers to prevent explosions from pressure build-up or leaks from damaged containers.
Do you have any other tips for liquid nitrogen safety? Leave a comment below.
Originally published 6 January 2014. Reviewed and updated November 2021.
- Tristan Kirk. Imperial College London fined £70,000 after scientist suffocated in lab filled with nitrogen. Evening Standard. 13 December 2017.
- Safety problems led to lab death. BBC News. 20 June 2000.
- Liquid nitrogen. Wikipedia. Accessed 16 November 2021