Cryogenics Storage FAQs
What is liquid nitrogen?
Liquid nitrogen is produced by cooling and compressing nitrogen gas to a liquid state at extremely low temperatures (−196°C). It is colorless, odorless, and widely used for freezing, cooling and preserving materials in science, medicine and food industries.
Nitrogen is an element that makes up 78% of the atmosphere, it has a boiling point of -196oC (77k) and therefore exists as a gas. Liquid nitrogen is created in large quantities at air separation plants as a clear odourless liquid, this liquid is utilised in many industries due to its extremely cold temperature. Liquid Nitrogen is made up of 99.999% nitrogen and traces of oxygen, moisture, and argon.
Why is it used in scientific research?
Liquid nitrogen is used in scientific research because its extremely low temperature (−196°C) allows scientists to rapidly freeze and preserve biological samples without damaging them. Its inert, non-toxic nature makes it safe for maintaining sample stability over long periods.
This extremely low temperature places samples in an “arrested” state, preventing chemical reactions and biological activity. This helps preserve both the physical structure and viability of materials, which is essential for long-term studies. Because many samples are irreplaceable, storage at liquid nitrogen temperatures is considered one of the safest and most reliable preservation methods.
What is Tg and why is it important.
Tg, or glass transition temperature, is the temperature at which a substance shifts into a glass-like, solid state without forming ice crystals. It is important because, below this temperature, biological samples can be preserved without structural damage, maintaining their stability and viability.
For long term storage liquid nitrogen, with a boiling temperature of -196°c, is recognised as the safest temperature because it is -64°c below the glass transition temperature (Tg) of water (-132°c). At this temperature neither solute, salt or ice-induced cellular damage occurs, cells effective survive in glasses between ice crystals. This is unlike in an ultra-low freezer where cellular damage can occur as ice crystals as well as physico-chemical damage can occur reducing the viability of cells
For more information see the study 'Effects of cryopreservation on viability and functional stability of an industrially relevant alga'.
How do liquid nitrogen vessels maintain temperature?
To maintain the internal cold temperature the vessels called dewars (named after Sir James Dewar in 1892) are double walled with a vacuum in between, vacuums are the best insulator so protect the samples from the higher external temperature.
However, vacuum alone is not sufficient to maintain the performance of the vessel, other factors such as foil & paper wraps and vacuum retention systems are necessary to produce a high quality, long lasting, dewar. The quality and longevity of the vacuum are of paramount important to the vessel and quality should be the first aspect looked at during the procurement stage.
What are liquid nitrogen vessels made from?
This depends on the size, smaller vessels are made from aluminium while larger vessels are made from stainless steel.
Aluminium is the material of choice for the smaller vessel as it is lightweight for easy transport of the dewar with good insulation properties. Large vessels, which hold heavier amounts of LN2 and product, are made from stainless steel. Stainless steel is ideal for liquid nitrogen dewars, it is weldable (key to building quality products that don’t ‘leak’), light weight, unbreakable and corrosion-resistant. As well as the construction benefits the stainless steel is also excellent for the maintaining the internal temperature as it reflects heat radiation well, has good thermal conductivity and has very low thermal expansivity when exposed to cryogenic temperatures.
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What is the difference between vapour phase and liquid phase?
Liquid phase involves immersing samples directly in liquid nitrogen at -196°C, ensuring maximum temperature stability but risking cross-contamination. Conversely, vapor phase stores samples in cold gas above the liquid, significantly reducing contamination risks and safety hazards like exploding vials, while maintaining slightly higher, yet safe, temperatures.
What needs to be considered for safety?
All users of liquid nitrogen must be trained on the safe handling of the element as although liquid nitrogen is nontoxic and chemically inert, the incredibly low temperature can cause potential injuries. Cryogenic burns and splash injuries can be prevented by the user wearing suitable gloves, aprons, eye protection and face shield.
The liquid to gas expansion ration of nitrogen is 1:694, therefore a large expansion occurs when the liquid is vapourised. If a leakage or major spillage occurs, then the nitrogen rapidly replaces the oxygen in the area which can quickly result in asphyxiation.
A spacious and well-ventilated area with low oxygen level monitors is essential to maintaining a high level of safety. Any alarms should ideally be local and remotely visually & audibly. Speak to us if you have any queries or concerns.
Why is Liquid Nitrogen a potential ‘green’ aspect to laboratories?
The production of liquid nitrogen is a potential way for companies/institutes to reduce their carbon footprint and energy consumptions. Liquid nitrogen is produced in large quantities as a by-product for the manufacturer of liquid oxygen for industrial processes and air separation plants. As the liquid nitrogen is a waste product it has a carbon emission of Zero and as liquid nitrogen dewars use limited or no energy it makes the overall process significantly more cost effective in the long run compared to other low temperature options such as ultra-low freezers (-80oC). Since, unlike mechanical freezers, there is no heat generated from a liquid nitrogen vessel there is no requirement to run high energy HVAC systems to control the room temperature. The energy savings are greater than 90% when compared to an ultra-low freezer and the only running cost is the liquid nitrogen itself to top up the cryostorage vessels.