There is a moment, familiar to anyone who has worked in an IVF laboratory or a research facility, when a dewar of liquid nitrogen is opened and a white cloud rolls silently across the bench. It is dramatic enough to feature in science fiction and common enough in reproductive medicine that embryologists barely notice it. But the physics behind it — and the practical consequences of getting it wrong — are worth understanding properly.

Liquid nitrogen is one of the most widely used industrial and scientific fluids on the planet. It is also one of the most misunderstood. The same substance that preserves embryos for decades is capable of causing severe injury in seconds if handled incorrectly. The same properties that make it invaluable in cryogenic laboratories make it inherently hazardous in confined spaces.

This is the complete guide: what liquid nitrogen actually is, how it behaves at the temperatures and pressures relevant to laboratory and clinical use, how to store it correctly, and what the genuine safety considerations are for anyone working with it.

What Is Liquid Nitrogen?

Liquid nitrogen is nitrogen in a liquid state at low temperature. It has a boiling point of approximately -196 degrees Celsius at atmospheric pressure. Nitrogen itself makes up roughly 78 percent of the atmosphere we breathe — it is the most abundant gas on Earth. At room temperature and standard pressure it exists as a colourless, odourless, largely inert diatomic gas. Cool it to -196 degrees Celsius and it becomes a colourless liquid with a viscosity roughly half that of water.

The transition from gas to liquid is what makes nitrogen useful as a cryogenic fluid. Liquid nitrogen occupies approximately 700 times less volume than the equivalent mass of nitrogen gas at room temperature. This density makes it practical to store and transport. Its boiling point of -196 degrees Celsius makes it capable of maintaining biological samples in a state of complete preservation indefinitely.

Liquid nitrogen is produced industrially by fractional distillation of liquid air — a process in which air is cooled until it liquefies and the constituent gases are separated by their different boiling points. It is a byproduct of liquid oxygen production and is widely available from industrial gas suppliers across the UK and globally.

Liquid Nitrogen Temperature and Storage Temperature

The key temperatures relevant to liquid nitrogen storage are as follows.

Boiling point at atmospheric pressure: -196 degrees Celsius (77 Kelvin, -321 degrees Fahrenheit). This is the temperature at which liquid nitrogen exists in an open dewar or storage vessel at sea level.

Glass transition temperature: -130 degrees Celsius. This is the threshold below which all molecular motion effectively stops and biological samples can be stored without measurable degradation. Any sample stored below -130 degrees Celsius is in a state of complete biological stasis.

Freezing point: -210 degrees Celsius. Liquid nitrogen freezes to a solid at this temperature, which is only relevant in highly specialised applications.

For cryopreservation of biological samples, the critical storage temperature is anything below -130 degrees Celsius. Liquid nitrogen storage tanks operating in vapour phase mode typically maintain temperatures between -140 and -196 degrees Celsius — well within the safe storage range for embryos, oocytes, sperm, stem cells, and cell lines.

Liquid Nitrogen Pressure: Dewars, Pressurised Vessels, and the Dewar Wall

Understanding liquid nitrogen pressure is essential for anyone selecting or maintaining cryogenic storage equipment. There are two fundamentally different types of liquid nitrogen vessel, and confusing them causes dangerous errors.

Non-pressurised dewars

A standard laboratory liquid nitrogen dewar — the type used in IVF clinics and research laboratories for sample storage — is a non-pressurised vessel. It is a vacuum-insulated flask, descended from the design Sir James Dewar developed in the late nineteenth century. The vessel has an outer wall and an inner wall separated by a vacuum: the dewar wall. This vacuum insulation dramatically reduces heat transfer from the environment into the liquid nitrogen, minimising evaporation and maintaining the cryogenic temperature without any external cooling system. Non-pressurised dewars operate at or near atmospheric pressure and are vented to the atmosphere through the neck opening. If a non-pressurised dewar is sealed completely — which should never happen — pressure builds rapidly and the vessel can fail catastrophically.

Pressurised liquid nitrogen dewars

A pressurised liquid nitrogen dewar is a different piece of equipment entirely. It is a sealed vessel designed to hold liquid nitrogen under pressure, typically between 22 and 350 psi depending on the application. Pressurised dewars are used for LN2 supply and dispensing, not for sample storage. They deliver liquid nitrogen under pressure to fill storage vessels, controlled-rate freezers, and automated supply systems. The pressure is maintained by controlled evaporation of a small amount of liquid nitrogen within the sealed vessel, building pressure that drives liquid delivery. Pressure relief valves prevent the pressure from exceeding safe design limits.

The dewar wall — the vacuum-insulated double wall structure — is what makes both types of vessel function. In a storage dewar, the integrity of the vacuum insulation is the single most important performance factor. A vacuum that degrades silently over time leads to increased LN2 consumption, reduced holding times, and eventually temperature instability that can compromise stored samples before anyone notices. This is why Cryolab provides a five-year vacuum warranty on the CryoBank Series — and why vacuum warranty terms are one of the most important specifications to examine when purchasing any large cryogenic storage tank.

Hazards of Liquid Nitrogen: What Actually Kills and Injures People

Liquid nitrogen safety is one of those subjects where the genuine risks are well-established, but poor training means they are frequently underestimated or misunderstood. There are four primary hazard categories.

Extreme cold and cryogenic burns

Cryogenic burns occur when liquid nitrogen or cold nitrogen vapour contacts skin or eyes. Unlike thermal burns, cryogenic burns are not always immediately painful due to the Leidenfrost effect — a thin vapour layer that briefly insulates the skin from direct contact. This causes people to underestimate the severity of the exposure. Prolonged or high-volume contact causes severe, deep tissue damage equivalent to serious thermal burns. Eyes are particularly vulnerable: brief exposures that cause no significant skin damage can cause permanent eye injury. The minimum PPE requirements for any liquid nitrogen handling task are cryogenic-rated gloves, a face shield, and a lab coat or overalls.

Asphyxiation

This is the hazard that causes fatalities. One litre of liquid nitrogen produces approximately 700 litres of nitrogen gas when it vaporises at room temperature. In an enclosed or poorly ventilated space, a small spill can displace enough oxygen to render the atmosphere lethal — without any perceptible warning. Nitrogen is colourless and odourless and gives no sensory indication of its presence. Oxygen depletion below 16 percent causes rapid unconsciousness. The UK Health and Safety Executive recommends maintaining oxygen concentrations above 19.5 percent in all workplaces where cryogenic materials are used. The Control of Substances Hazardous to Health (COSHH) Regulations 2002 classify liquid nitrogen as a substance hazardous to health. The British Compressed Gases Association Code of Practice 30 provides the primary UK guidance document for safe use of liquid nitrogen dewars. Continuous oxygen monitoring with audible alarms is a mandatory control measure in any room where liquid nitrogen is stored or regularly used.

Pressure buildup in sealed containers

Rapid evaporation can cause pressure buildup in sealed containers, creating a catastrophic failure risk. This is why non-pressurised dewars must never be sealed. It is also why cryovials stored in liquid phase liquid nitrogen can fail at thaw if liquid nitrogen has entered the vial through a damaged or poorly fitting cap. High security hermetically sealed cryogenic tubes such as the CBS High Security range from Cryolab are designed to prevent this by eliminating liquid nitrogen ingress entirely.

Material embrittlement

Carbon steel, standard plastics, and rubber become brittle at cryogenic temperatures and can fracture under stress. Equipment used with liquid nitrogen must be rated for cryogenic service. Using non-rated fittings, hoses, or transfer equipment can result in sudden brittle fracture and uncontrolled spillage.

Liquid Nitrogen Tank Safety: The Practical Checklist

For laboratory and clinical settings using liquid nitrogen for cryopreservation, the following are the minimum safety requirements.

Ventilation and oxygen monitoring: liquid nitrogen must always be stored and used in well-ventilated areas. Storage rooms must have oxygen depletion monitoring with alarms set to alert at or above 19.5 percent oxygen concentration. This is not optional in any facility storing biological samples under COSHH regulations.

PPE: cryogenic gloves, face shield, and lab coat or overalls are required for any liquid nitrogen handling. Open footwear is unacceptable. Standard laboratory gloves do not provide adequate protection against cryogenic temperatures.

Dewar handling: handle with care at all times as rough handling can cause serious damage to the dewar and spillage. Do not walk, roll or drag dewars. Always protect the vessel from severe jolting and impact.

Transfer: liquid nitrogen should only be transferred using equipment rated for cryogenic use. Vacuum-jacketed transfer hoses minimise boil-off and reduce spillage risk during filling operations.

Monitoring: continuous LN2 level monitoring with remote alarm capability is a regulatory requirement for HFEA-licensed fertility facilities and best practice for all facilities storing biological samples in liquid nitrogen.

Training: all staff handling liquid nitrogen must be trained before first use, with records of training maintained by the laboratory manager or safety officer.

How Liquid Nitrogen Is Used in Biological Cryopreservation

In biological cryopreservation, liquid nitrogen is used in two ways: as the cooling medium during vitrification and as the long-term storage medium in liquid nitrogen storage tanks.

In vitrification, the sample is loaded onto a vitrification device and plunged directly into liquid nitrogen. The cooling rate exceeds 15,000 degrees Celsius per minute, converting the cellular fluid from liquid to a glass-like amorphous solid without forming crystals. This is the defining technique in modern IVF embryo and oocyte cryopreservation, achieving post-warming survival rates consistently above 90 percent in experienced laboratories.

In controlled-rate slow cooling — used for sperm, red blood cells, and certain stem cell types — a controlled-rate freezer uses liquid nitrogen vapour to cool the sample at a precisely programmed rate before transfer to long-term storage. The CBS Digitcool range from Cryolab provides four chamber sizes from 11.5 to 150 litres, covering every scale of clinical and research application.

In both cases, once frozen, samples are transferred to a liquid nitrogen storage dewar for long-term preservation. The CryoCan 47-10 and CryoNest XL are designed for the reliability and holding times that clinical sample storage demands. For biobank-scale storage, the CryoBank Series stores between 15,000 and 95,000 samples in vessels from 350 to 1,800 litres.

Price of Liquid Nitrogen in the UK

The price of liquid nitrogen in the UK varies significantly depending on volume, delivery frequency, and supplier contract terms. Bulk liquid nitrogen delivered by tanker typically costs between £0.10 and £0.30 per litre for large volumes. Small dewar quantities purchased from industrial gas suppliers cost considerably more per litre, often £0.50 to £2.00 depending on volume and contract.

For clinical and research facilities, LN2 cost is a meaningful operational expense. Automated supply systems integrated into the CryoBank Series use vacuum-jacketed transfer hoses and solenoid valve delivery to minimise nitrogen consumption and reduce ongoing costs. A tank with poor vacuum integrity can consume significantly more LN2 than a well-maintained equivalent, making the purchase price of a dewar a poor proxy for its total cost of ownership.

Frequently Asked Questions About Liquid Nitrogen

What is liquid nitrogen?

Liquid nitrogen is nitrogen gas cooled to -196 degrees Celsius, at which point it becomes a colourless, odourless liquid. It is produced by fractional distillation of liquid air and is used as a cryogenic fluid in biology, medicine, food processing, manufacturing, and research.

What temperature is liquid nitrogen stored at?

At atmospheric pressure, liquid nitrogen exists at -196 degrees Celsius. Biological samples are stored at this temperature in liquid phase, or at between -140 and -190 degrees Celsius in vapour phase storage systems.

What are the hazards of liquid nitrogen?

The four primary hazards are cryogenic burns from skin or eye contact, asphyxiation from oxygen displacement in poorly ventilated spaces, pressure buildup in sealed containers, and material embrittlement of non-rated equipment.

What is the dewar wall?

The dewar wall is the vacuum-insulated double wall structure of a liquid nitrogen storage vessel. The vacuum between the inner and outer walls reduces heat transfer, maintaining cryogenic temperatures with minimal LN2 consumption. The integrity of the dewar wall vacuum is the most important performance factor in any cryogenic storage vessel.

What is the price of liquid nitrogen in the UK?

Bulk delivered liquid nitrogen typically costs between £0.10 and £0.30 per litre. Small dewar quantities cost more per litre. Prices vary by supplier, volume, and contract terms.

How long does liquid nitrogen last in a storage tank?

Holding time depends on tank size, vacuum insulation quality, and usage. Well-maintained liquid nitrogen storage dewars hold LN2 for between 30 and 90 days or more without a top-up. The CryoCan 47-10 and CryoNest XL are designed for market-leading holding times.