Safety data sheet · UN 1066
Nitrogen (N₂) Safety Data Sheet
Nitrogen (N₂, CAS 7727-37-9, UN 1066) is inert, non-toxic and non-flammable, and kills by displacing oxygen with no warning whatsoever. It has no smell and produces no sensation of breathlessness. Confined space entry after a nitrogen purge requires oxygen monitoring, without exception.
- UN number (compressed)
- UN 1066
- UN number (refrigerated liquid)
- UN 1977
- CAS number
- 7727-37-9
- Molecular weight
- 28.0134 g/mol
- Normal boiling point
- −195.8 °C
- Product
- Nitrogen, compressed
- CAS number
- 7727-37-9
- UN number
- UN 1066
- Transport class
- 2.2 — Non-flammable, non-toxic gas
- Specification
- IS 1747
- Revision
- 1 · 6 August 2026
Also known as: N₂ · Liquid nitrogen when refrigerated · LIN
Section 1 — Identification
Product name: Nitrogen, compressed Chemical formula: N₂ CAS number: 7727-37-9 · EC number: 231-783-9 · UN number: UN 1066 Specification: IS 1747
Identified uses: Purging, blanketing and inerting; pressure transfer; laser cutting assist gas; controlled atmospheres for heat treatment; root purging; food packaging; cryogenic cooling and freezing (liquid). Uses advised against: Ventilation or cooling of personnel or workspaces. Blowing down clothing. Any use in a confined space without oxygen monitoring.
Supplier: The Kamrup Industrial Gases Limited.
Section 2 — Hazards identification
GHS classification: Gases under pressure — compressed gas (refrigerated liquefied gas for the liquid product).
Signal word: WARNING
Hazard statements
- H280 — Contains gas under pressure; may explode if heated.
- (Refrigerated liquid) H281 — Contains refrigerated gas; may cause cryogenic burns or injury.
The hazard the classification does not capture. Nitrogen has no harmonised health-hazard classification because it is not toxic. That has repeatedly led people to treat it as harmless. Nitrogen asphyxiates without any warning at all — no smell, no irritation, and critically no sensation of breathlessness, because the body’s urge to breathe responds to carbon dioxide build-up rather than to oxygen shortage.
Loss of consciousness can occur within one or two breaths in a nitrogen-rich atmosphere.
Section 3 — Composition
| Component | CAS | Concentration |
|---|---|---|
| Nitrogen | 7727-37-9 | ≥99.5 % (industrial, IS 1747); higher grades on request |
Single-substance product.
Section 4 — First aid
Inhalation. Remove to fresh air — but do not enter an oxygen-deficient atmosphere without air-supplied breathing apparatus and a standby person. Rescuer fatalities are a recurring feature of nitrogen incidents. Give oxygen if trained. If breathing has stopped, give artificial respiration. Seek immediate medical attention.
Skin contact (liquid or cold gas). Cold burns: flush with copious tepid water, do not rub, do not apply direct heat, cover loosely with a sterile dressing and seek immediate medical attention.
Eye contact (liquid or cold gas). Flush with tepid water for at least 15 minutes. Seek immediate medical attention.
Section 5 — Firefighting
Non-flammable and does not support combustion. Nitrogen will extinguish fire by displacing oxygen.
Specific hazards. Cylinders exposed to fire may rupture. Cool from a protected position or evacuate. Discharge into a confined space during firefighting creates an asphyxiating atmosphere.
Section 6 — Accidental release
Evacuate and ventilate. Do not enter the affected area without oxygen monitoring and, where the atmosphere is or may be deficient, air-supplied breathing apparatus.
For a liquid spill, note the large expansion on vaporisation: a modest volume of liquid produces a very large volume of gas and can render a room oxygen-deficient quickly. Also treat the cold hazard to personnel and the embrittlement hazard to floors, drains and equipment not rated for cryogenic temperatures.
Section 7 — Handling and storage
Gas. Secure cylinders upright. Open valves slowly. Never use nitrogen for ventilation, cooling or blowing down. Ensure adequate ventilation wherever nitrogen is discharged.
Liquid. Handle only with cryogenic gloves, face shield and covered footwear. Use only vessels designed and rated for cryogenic service. Never seal liquid nitrogen in a closed container — vaporisation will rupture it. Ensure the storage area is well ventilated and, where volumes warrant it, fitted with oxygen monitoring.
Confined spaces. Any vessel, pit or enclosure that has been purged with nitrogen must be treated as an oxygen-deficient atmosphere until measurement proves otherwise. Measure before entry, monitor continuously during entry, and post a standby person outside.
Section 8 — Exposure controls
Nitrogen has no occupational exposure limit because it is not toxic. The control parameter is oxygen concentration, not nitrogen concentration.
Entry to any space where nitrogen may be present requires oxygen measurement. 19.5 % oxygen is the widely used minimum for safe entry.
Personal protection: oxygen monitoring for confined-space work; air-supplied breathing apparatus where deficiency is possible; cryogenic gloves, face shield and covered footwear for liquid handling.
Section 9 — Physical and chemical properties
| Property | Value | Source |
|---|---|---|
| Physical state | Gas (compressed) or cryogenic liquid | — |
| Appearance | Colourless | — |
| Odour | Odourless | — |
| Molecular weight | 28.0134 g/mol | NIST |
| Normal boiling point | −195.8 °C (77.34 K) | NIST |
| Triple point | −210.0 °C (63.14 K) at 0.1252 bar | NIST |
| Critical temperature | −146.96 °C (126.19 K) | NIST |
| Critical pressure | 33.978 bar | NIST |
| Vapour density (air = 1) | ≈0.97 — very close to air | Literature |
| Flammability | Non-flammable | — |
| Oxidising properties | None | — |
Vapour density ≈0.97 is a hazard in itself. Nitrogen is almost exactly as dense as air, so a release neither rises and disperses nor settles predictably into a known low point. It simply mixes and lingers wherever ventilation is poor. Do not assume a leak will clear itself.
Thermophysical constants from the NIST Chemistry WebBook (public domain). Remaining values are standard literature.
Section 10 — Stability and reactivity
Stable and chemically inert under normal conditions.
Conditions to avoid: heat, and for the liquid, contact with materials not rated for cryogenic service, which may embrittle and fail.
Note. Although inert at ambient temperature, nitrogen dissociates in a welding arc and can form nitrides in weld metal — the reason it is not used as a general shielding gas. See argon.
Section 11 — Toxicological information
Not toxic. A simple asphyxiant. Symptoms of oxygen deficiency progress rapidly from impaired coordination and judgement to unconsciousness and death, typically without the casualty recognising anything is wrong.
Section 12 — Ecological information
Not classified as environmentally hazardous. Nitrogen is the principal component of air; release causes no ecological harm.
Section 13 — Disposal
Vent to atmosphere in a safe, well-ventilated outdoor location away from confined spaces, pits and building intakes. Return cylinders to the supplier.
Section 14 — Transport
| UN number | UN 1066 (compressed) · UN 1977 (refrigerated liquid) |
| Proper shipping name | NITROGEN, COMPRESSED |
| Class | 2.2 |
Transport upright and secured, valves closed, caps fitted, in a ventilated vehicle. Never carry cylinders in an enclosed passenger compartment.
Section 15 — Regulatory information
- Gas Cylinders Rules, 2016 (PESO)
- IS 1747 — compressed nitrogen specification
- IS 7285 — seamless steel cylinders
- IS 3224 — cylinder valves
- EN ISO 14175 — nitrogen in welding shielding gas classification
- ADR 2025 — UN 1066 / UN 1977
Section 16 — Other information
Revision 1, issued 6 August 2026.
Relates to nitrogen as supplied and does not release the user from assessing their own installation and application. A signed PDF copy is available on request for audit files; this HTML page is the current version.
Nitrogen — frequently asked questions
If nitrogen is 78 % of the air I breathe, how can it be dangerous?
Because the danger is not the nitrogen — it is the absence of oxygen. Air is safe because the other 21 % is oxygen. An atmosphere of pure nitrogen contains none, and a person entering it can lose consciousness in one or two breaths. This is the single most misunderstood industrial gas hazard.
Will I feel breathless before I collapse?
No, and this is what makes nitrogen lethal. The urge to breathe is triggered by rising carbon dioxide in the blood, not by falling oxygen. In a nitrogen atmosphere you continue to exhale CO₂ normally, so no alarm is raised physiologically. People lose consciousness without any warning sensation at all.
Is it safe to enter a vessel after nitrogen purging if it has been left open?
Not on that basis alone. Nitrogen and air mix slowly in a still vessel, and pockets persist for far longer than intuition suggests, particularly in low corners and beneath internal structures. **Measure the oxygen concentration before entry, and continue monitoring throughout.**
Why do so many nitrogen fatalities involve two people?
Because the first casualty collapses silently and the second enters to help without breathing apparatus. Rescuer deaths are a recurring pattern in confined-space nitrogen incidents. Never enter to rescue without air-supplied respiratory protection and a standby person.
What are the hazards specific to liquid nitrogen?
Severe cold burns on contact, at −195.8 °C. Embrittlement of materials not rated for cryogenic service. And a very large expansion ratio on vaporising, so a small spill produces a large volume of gas and can displace the oxygen in a room quickly. Liquid nitrogen must never be handled in a sealed container.
Can nitrogen be used to blow down clothing or clear a workspace?
No. Use compressed air. Directing nitrogen at a person or into a small enclosed space creates an oxygen-deficient atmosphere in seconds.
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