Guide
Liquid nitrogen: temperature density, expansion ratio, hazards and safe handling of dewars
Liquid nitrogen (LN₂, formula N₂) boils at −195.8 °C at atmospheric pressure, has a density of about 806 kg/m³ (specific gravity 0.81) and expands roughly 694 times into gas at 21 °C. It is not flammable. Its hazards are asphyxiation, cold burns, pressure build-up in closed vessels and oxygen condensing out of the surrounding air.
- Boiling point
- −195.8 °C
- Liquid density
- About 806 kg/m³ at the normal boiling point
- Expansion ratio
- About 1:694 liquid to gas at 21 °C and 1 atm; about 1:680 at 15 °C
- Latent heat of vaporisation
- About 199 kJ/kg
- Oxygen deficiency
- Below 11 % oxygen
Liquid nitrogen is nitrogen cooled below its boiling point of −195.8 °C, the coldest liquid most factories, laboratories and hospitals will ever handle. It is odourless, colourless, non-flammable and chemically quiet, which is exactly why it causes accidents: nothing about it warns you. The figures on this page are from the NIST Chemistry WebBook unless stated, and the safety guidance follows EIGA and AIGA documents. For the gas itself, see the nitrogen technical data sheet.
Liquid nitrogen properties at a glance
| Property | Value | Source |
|---|---|---|
| Formula | N₂ (trade names LN₂, LIN) | — |
| Molar mass | 28.013 g/mol | NIST |
| Normal boiling point, 1.013 bar | −195.8 °C (77.35 K) | NIST |
| Triple point | −210.0 °C, 0.125 bar | NIST |
| Critical point | −146.96 °C, 33.96 bar | NIST |
| Liquid density at boiling point | about 806 kg/m³ | NIST saturation table |
| Specific gravity of liquid (water = 1) | about 0.81 | From NIST density |
| Gas density, 0 °C and 1 atm | 1.250 kg/m³ | NIST |
| Liquid-to-gas expansion | about 1:680 at 15 °C, about 1:694 at 21 °C | Computed from NIST densities |
| Latent heat of vaporisation | about 199 kJ/kg (about 160 kJ/L) | NIST |
| Liquid Cp at boiling point | about 2.04 kJ/kg·K | NIST saturation table |
| Liquid viscosity at boiling point | about 160 µPa·s | NIST saturation table |
| UN number and class | UN 1977, Class 2.2 | UN Model Regulations |
Two numbers explain most of the behaviour. The expansion ratio means one litre of liquid becomes nearly 0.7 m³ of gas at room temperature. The latent heat is low, about 199 kJ/kg against roughly 2,257 kJ/kg for water at 100 °C (both NIST), so liquid nitrogen boils off quickly whenever heat reaches it, and a warm surface dropped into it produces a burst of gas rather than slow cooling.
Composition depends on the grade ordered. IS 1747:2023 allows liquid supply only in the purer grades, N 4.5 (99.995 %), N 5.0 (99.999 %) and N 5.5 (99.9995 %), with oxygen limits of 10, 2 and 1 ppm. The 99.5 % N 2.5 grade is gas only. Liquid is vaporised and analysed in the gas phase.
Is liquid nitrogen flammable or toxic?
Neither. Nitrogen does not burn and is not a poison; it is 78 % of the air you are breathing now. The hazards are physical, and there are four of them.
Asphyxiation
Nitrogen displaces oxygen. The EIGA's 2026 safety information on cryosaunas sets out what happens as oxygen falls:
| Oxygen, % by volume | Effect (EIGA SI 19/26) |
|---|---|
| 18 to 21 | No discernible symptoms |
| 11 to 18 | Reduced physical and mental performance, not noticed by the person |
| 8 to 11 | Possible fainting within minutes, with no warning; risk of death below 11 % |
| 6 to 8 | Fainting after a short time; resuscitation possible if immediate |
| 0 to 6 | Near-immediate fainting; brain damage even if rescued |
EIGA also notes that as little as two breaths in an oxygen-deficient atmosphere can cause unconsciousness. A worked example shows how little liquid it takes. A 20 litre dewar knocked over in a closed 30 m³ storeroom releases about 16 kg of nitrogen, or about 14 m³ of gas at 20 °C. If that gas pushes the same volume of air out of the room, oxygen falls to about 11 %, the level EIGA links with fainting and risk of death; even if it simply mixes in, oxygen falls to about 14 %. Cold vapour from a spill is heavier than air and collects at floor level and in pits first. The full treatment is on nitrogen asphyxiation.
Cold burns and embrittlement
At −196 °C liquid nitrogen and anything it has cooled will freeze skin on contact. Brief splashes often skid off on a vapour film, which encourages carelessness; liquid soaking into a glove, a cuff or a shoe does not skid off. Ordinary carbon steel turns brittle at these temperatures, which is why cryogenic vessels and pipework are built from austenitic stainless steel, aluminium or copper alloys, and why a spill on a steel floor plate or a carbon-steel pipe rack can crack it.
Pressure build-up
Liquid nitrogen is always boiling. In a closed container the gas has nowhere to go, and at an expansion of about 694 times the pressure climbs until something gives. Every cryogenic container therefore has a vent path: a loose neck plug on an open dewar, a relief valve and bursting disc on a liquid cylinder, and duplicated relief devices on a bulk tank. A section of pipe with liquid trapped between two closed valves is a pressure vessel with no relief, and needs its own relief valve.
Oxygen condensation
Oxygen boils at −182.96 °C, about 13 K above nitrogen. Any surface at liquid-nitrogen temperature will therefore condense air, and the liquid that drips off is richer in oxygen than air. An open dewar left standing for days also enriches in oxygen, because nitrogen boils off preferentially. Keep oil, grease and combustible lagging away from uninsulated cold lines, and do not let liquid air drip onto asphalt or wood. Oxygen enrichment covers the fire side of this.
Rules that matter
The rules below follow EIGA and AIGA practice for cryogenic air gases. Container types are compared on cryogenic cylinders, dewars and tanks.
Handling liquid nitrogen dewars
- Wear a face shield over safety glasses, loose-fitting insulated or cryogenic gloves that can be shaken off, long sleeves and trousers worn over the shoes. No watches or rings on the hands that pour.
- Fill and decant in a well-ventilated area, never in a lift, car or small closed room. Transport a dewar in a lift on its own, with nobody riding with it.
- Use only containers designed for cryogenic liquid. A domestic vacuum flask has no vent path and can burst.
- Keep pressurised liquid cylinders upright. Laboratory guidance from Lawrence Berkeley National Laboratory warns never to operate a tilted cylinder or lay one on its side.
- Lower objects into the liquid slowly with tongs; a warm object causes violent boiling and splashing.
- Fit a fixed oxygen monitor with a low-level sensor in any room where liquid nitrogen is stored or decanted, alarmed at 19.5 to 20 %. EIGA's cryosauna guidance uses 20 %.
- Check relief valves and bursting discs are present and undamaged on every pressurised container. AIGA 030/13 asks that relief devices be tested to EIGA Doc 24 and notes that bursting discs may need periodic replacement.
Uses of liquid nitrogen in India
| Use | What the liquid does | Note |
|---|---|---|
| Artificial insemination, semen and embryo banks | Stores frozen straws at about −196 °C in vapour or liquid phase for years | A widespread distributed use in rural India, through dairy co-operatives and state livestock departments |
| Food freezing | Tunnel and immersion freezing of seafood, meat, bakery and ready meals | Fast freezing gives small ice crystals and better texture |
| Shrink-fitting | Cools a shaft, bush or liner so it contracts and slides into place | Contraction is small but enough for an interference fit; check both parts are rated for the cold |
| Cryotherapy and dermatology | Freezing warts and lesions; whole-body cryo-cabins | EIGA SI 19/26 applies to open cryo-cabins |
| Cryogenic grinding | Embrittles plastics, rubber and spices before milling | Prevents heating and loss of volatile oils |
| Laboratories | Cold traps, sample storage, cooling detectors | Small dewars, frequent decanting |
| Bulk gas | Vaporised on site as a high-purity nitrogen supply | Alternative to a PSA nitrogen plant where very high purity, or a reserve that needs no power, is wanted |
The broader set of nitrogen applications, including gas-phase uses, is on uses of nitrogen gas.
How KIGL supplies liquid nitrogen
KIGL fills compressed nitrogen in cylinders at its own PESO-approved works at Noonmati, Guwahati, and Howrah, Kolkata. Liquid nitrogen is a different product, made by cryogenic air separation; KIGL operates an air separation plant and supplies liquid nitrogen. For high-purity gas without liquid logistics, KIGL also builds on-site PSA nitrogen plants. Product grades and cylinder supply are on the nitrogen page, and first aid and fire-fighting information is on the nitrogen safety data sheet.
Rules that matter
Rules to apply
- Treat every litre of liquid nitrogen as 0.7 m³ of gas waiting to be released into the room it is in.
- Never seal a container, and never trap liquid between two closed valves.
- Monitor oxygen at low level wherever liquid is stored or used indoors; the body will not warn you.
- Keep skin, eyes and carbon steel away from the liquid and from anything it has cooled.
- Keep oil and combustibles off cold surfaces, where condensed air is oxygen-rich.
Liquid nitrogen — frequently asked questions
Is liquid nitrogen flammable?
No. Nitrogen does not burn and does not support combustion, and liquid nitrogen is classed as UN 1977, Class 2.2, a non-flammable, non-toxic gas. It can still feed a fire indirectly: at −195.8 °C it is colder than the boiling point of oxygen, so air condenses on cold pipework and an open dewar slowly enriches in oxygen as the nitrogen boils away first.
What is the density of liquid nitrogen?
About 806 kg/m³ at its normal boiling point, from the NIST Chemistry WebBook (806.1 kg/m³ at 1.013 bar and −195.8 °C). One litre therefore weighs about 0.81 kg. Liquid nitrogen is the lightest of the common cryogens: liquid oxygen is about 1,141 kg/m³ and liquid argon about 1,395 kg/m³. Density falls as the liquid warms under pressure in a tank.
What is the specific gravity of liquid nitrogen?
About 0.81 against water, from a NIST liquid density of 806 kg/m³ at −195.8 °C. That is why liquid nitrogen floats on water while it boils violently, and why a 50 litre dewar holds only about 40 kg of product. Specific gravity of the gas is a different number: cold-end vapour is heavier than air, while nitrogen gas at room temperature is 0.967 times as dense as air.
What is the chemical formula of liquid nitrogen?
N₂, the same diatomic molecule as nitrogen gas. Trade shorthand is LN₂ or LIN. Commercial liquid nitrogen from an air separation unit is very pure; IS 1747:2023 allows liquid supply in grades N 4.5 (99.995 %), N 5.0 (99.999 %) and N 5.5 (99.9995 %), while the N 2.5 grade at 99.5 % is gas only. The impurities are mainly oxygen and argon.
Why must a liquid nitrogen container never be sealed?
Because the liquid never stops boiling. Heat leaking through even the best vacuum insulation turns liquid into gas at about 694 times its volume, and a closed container has nowhere to put it. Open dewars use a loose-fitting neck plug; pressurised liquid cylinders carry a relief valve and a bursting disc. Never fit a tight stopper, tape a lid or trap liquid between valves.
What are the risks of liquid nitrogen cryotherapy?
Asphyxiation above all. EIGA's 2026 safety information on cryosaunas, issued after a fatality, notes that oxygen near the occupant's face can fall sharply in open cabins fed directly with nitrogen. It asks for oxygen monitors in both the cabin and the room, extraction and an alarm at 20 % oxygen, continuous trained supervision, and leak checks whenever the liquid outlet valve is opened.
References
- Asia Industrial Gases Association. (2013). Storage of cryogenic air gases at users' premises (reproduced with EIGA permission) (AIGA 030/13). https://asiaiga.org/uploaded_docs/AIGA%20030_13_Storage%20of%20cryogenic%20air%20gases%20at%20users'%20premises.pdf
- Bureau of Indian Standards. (2021). Identification of the contents of industrial gas cylinders (IS 4379:2021, Second Revision).
- Bureau of Indian Standards. (2023). Nitrogen, compressed gas and liquid — Specification (IS 1747:2023, Second Revision).
- EIGA Safety Info 19/26, Nitrogen Hazards in Cryosaunas https://www.eiga.eu/uploads/documents/SI019.pdf
- Lawrence Berkeley National Laboratory EHS — pressurised dewars and cryogenic liquid cylinders https://ehs.lbl.gov/service/cryogenic-liquid-safety/pressurized-dewarscryogenic-liquid-cylinders/
- Linstrom, P. J., & Mallard, W. G. (Eds.). (n.d.). NIST Chemistry WebBook (NIST Standard Reference Database 69). National Institute of Standards and Technology. [thermophysical properties of nitrogen (saturation tables)] https://webbook.nist.gov/cgi/cbook.cgi?ID=C7727379
Enquiries
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