Safety data sheet · UN 1049
Hydrogen (H₂) Safety Data Sheet
Hydrogen (H₂, CAS 1333-74-0, UN 1049) is extremely flammable in air across an exceptionally wide band, 4 % to 75 %, and burns with a nearly invisible pale-blue flame. At 0.0837 kg/m³ it is the lightest gas there is, so it rises and collects overhead rather than pooling at floor level.
- UN number (compressed)
- UN 1049
- CAS number
- 1333-74-0
- Flammable range in air
- 4.0 % to 75.0 %
- Autoignition temperature
- ≈565 °C
- Flame visibility
- Nearly invisible in daylight
- Product
- Hydrogen, compressed
- CAS number
- 1333-74-0
- UN number
- UN 1049
- Transport class
- 2.1 — Flammable gas
- Revision
- 1 · 10 August 2026
Also known as: H2 · Dihydrogen · Compressed hydrogen
Section 1 — Identification
Product name: Hydrogen, compressed Chemical formula: H₂ CAS number: 1333-74-0 · EC number: 215-605-7 · UN number: UN 1049
Identified uses: Reducing atmospheres in heat treatment and metallurgy; hydrogenation; ammonia and methanol synthesis; generator cooling in power stations; carrier and fuel gas in laboratory instruments; fuel cells. Uses advised against: Any service using equipment not rated for hydrogen. Any use in an unventilated enclosed space.
Supplier: The Kamrup Industrial Gases Limited.
Section 2 — Hazards identification
GHS classification: Flammable gases — Category 1. Gases under pressure — compressed gas.
Signal word: DANGER
Hazard statements
- H220 — Extremely flammable gas.
- H280 — Contains gas under pressure; may explode if heated.
The two facts that define this gas.
It is flammable from 4 % to 75 % in air. Most fuel gases give you a narrow band in which a leak is dangerous. Hydrogen gives you almost the entire range between pure air and pure gas. Practically, any leak that mixes with air at all should be assumed ignitable, and the ignition energy required is very low — static discharge from clothing will do it.
The flame is nearly invisible. Hydrogen burns to water vapour with essentially no soot, so there is nothing glowing to see. In daylight a substantial hydrogen fire can be effectively invisible, and people have walked into one. It also radiates little heat sideways, so the usual instinctive warning of approaching a fire is absent.
Section 3 — Composition
| Component | CAS | Concentration |
|---|---|---|
| Hydrogen | 1333-74-0 | >99 % |
Single-substance product.
Section 4 — First aid
Inhalation. Hydrogen is a simple asphyxiant. Remove to fresh air — but do not enter an oxygen-deficient or potentially flammable atmosphere without air-supplied breathing apparatus and a standby person outside. Give oxygen if trained. If breathing has stopped, give artificial respiration. Seek immediate medical attention.
Burns. Treat as thermal burns. Because the flame is invisible, assess for burns even where the casualty reports no flame — cool with water, do not remove adhered clothing, cover with a sterile dressing and seek immediate medical attention.
Skin or eye contact (rapidly expanding gas). Frostbite is possible near the point of release. Flush with tepid water, do not rub, and seek medical attention.
Section 5 — Firefighting
Suitable media: Dry chemical, carbon dioxide. Water spray to cool surrounding cylinders and structures.
The rule that matters: stop the flow, do not extinguish the flame. Putting out a hydrogen flame while gas continues to escape converts a controlled burn into an unignited flammable cloud, which will reach another ignition source and deflagrate. Isolate the supply if it can be done safely. If it cannot, let the flame burn and protect everything around it.
Specific hazards. Cylinders exposed to fire may rupture. Cool from a protected position or evacuate. Use a thermal camera or a raised broom straw to locate an invisible flame before approaching.
Section 6 — Accidental release
Evacuate and eliminate all ignition sources — flames, hot surfaces, electrical switching, static, mobile phones, vehicles. Ventilate at high level: hydrogen rises immediately and collects under roofs, in ceiling voids and at the tops of stairwells.
Do not approach a suspected leak without checking for an invisible flame. Do not attempt to stop a leak against pressure. Isolate upstream where it is safe to do so.
Section 7 — Handling and storage
Equipment. Hydrogen-rated regulators, hoses and fittings only, with the left-hand thread connection that exists to prevent cross-connection. Never adapt a fitting, never substitute equipment from another gas service, and use no oil or grease anywhere in the system.
Bonding and earthing. Ground and bond the system. Static discharge is a sufficient ignition source for hydrogen.
Handling. Secure cylinders upright. Open valves slowly. Check for leaks with soap solution or a hydrogen-specific detector — never with a flame.
Storage. Well-ventilated area with ventilation at high level, separated from oxidisers, particularly oxygen and nitrous oxide. Keep away from heat, sparks and open flames, secured, capped, and below 52 °C. Outdoor or purpose-built storage is preferred.
Section 8 — Exposure controls
Hydrogen has no occupational exposure limit; it is not toxic. Two control parameters apply.
Flammability. Keep the atmosphere well below the 4 % lower flammable limit. Fixed detection should be positioned at high level, and calibrated for hydrogen.
Oxygen concentration. 19.5 % is the widely used minimum for safe entry.
Personal protection: flame-resistant clothing, anti-static footwear, face shield and gloves when making and breaking connections. Non-sparking tools. Intrinsically safe electrical equipment in the hazardous area.
Section 9 — Physical and chemical properties
| Property | Value | Source |
|---|---|---|
| Physical state | Gas (compressed) | — |
| Appearance | Colourless | — |
| Odour | Odourless — no warning property whatsoever | — |
| Molecular weight | 2.016 | Group technical data |
| Normal boiling point | −252.8 °C | Group technical data |
| Critical temperature | −240.0 °C | Group technical data |
| Critical pressure | 188 psia (≈12.96 bar) | Group technical data |
| Vapour density | 0.0837 kg/m³ at 21.1 °C | Group technical data |
| Specific volume | 192 ft³/lb at 21.1 °C, 1 atm | Group technical data |
| Flammable limits in air | Lower 4.0 % · Upper 75.0 % | Group technical data |
| Autoignition temperature | ≈565 °C | Group technical data |
| Water solubility | Very slightly soluble | Group technical data |
Odourless, colourless, invisible in flame, ignitable across seventy-one percentage points of mixture, and lighter than everything. Hydrogen removes every sensory warning a person normally relies on. Detection instruments are not a refinement here; they are the only thing standing between an operator and an atmosphere they cannot perceive.
Constants from group technical data.
Section 10 — Stability and reactivity
Stable under normal conditions.
Incompatible materials: Oxidisers — oxygen, chlorine, fluorine, nitrous oxide. Hydrogen forms explosive mixtures with air and with oxygen across a wide range.
Conditions to avoid: Heat, sparks, open flames, static discharge and all other ignition sources.
Materials of construction. Hydrogen can embrittle certain steels at pressure. Use only materials specified for hydrogen service.
Section 11 — Toxicological information
Not toxic. A simple asphyxiant. In high concentration it displaces oxygen and causes rapid breathing, headache, dizziness, unconsciousness and death depending on the degree of deficiency. There are no chronic effects.
The realistic hazard to a person is fire and explosion, not toxicity.
Section 12 — Ecological information
Not classified as environmentally hazardous. Hydrogen burns to water vapour.
Section 13 — Disposal
Vent to atmosphere only through a properly designed and located vent stack, in a safe outdoor location, clear of ignition sources, building intakes, and any overhanging or roofed structure where the rising gas could accumulate. Return cylinders to the supplier.
Section 14 — Transport
| UN number | UN 1049 |
| Proper shipping name | HYDROGEN, COMPRESSED |
| Class | 2.1 — Flammable gas |
| Labels | 2.1 |
Transport upright and secured, valves closed, caps fitted, in an open or well-ventilated vehicle. Never carry hydrogen cylinders in an enclosed passenger compartment. Segregate from oxidisers in transit.
Section 15 — Regulatory information
- Gas Cylinders Rules, 2016 (PESO)
- IS 7285 — seamless steel cylinders
- IS 3224 — cylinder valves
- IS 4379 — cylinder identification colours
- ADR 2025 — UN 1049
Section 16 — Other information
Revision 1, issued 10 August 2026.
Relates to hydrogen 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.
Hydrogen — frequently asked questions
What makes hydrogen more dangerous than other fuel gases?
Two things together. The flammable range runs from **4 % to 75 %** in air, so almost any leak that mixes at all produces an ignitable atmosphere — where most fuel gases give you a narrow window, hydrogen gives you nearly the whole span. And it ignites on very little energy, so static from clothing or an ungrounded fitting is enough.
Is it true you cannot see a hydrogen flame?
Effectively, yes, in daylight. Hydrogen burns to water vapour with almost no soot, so there is nothing incandescent to make the flame visible — it is pale blue and washes out completely in sunlight. There have been serious burn injuries to people who walked into a hydrogen flame they had no way of seeing. Where a leak is suspected, a broom straw or thermal camera held ahead of you is the traditional and still correct answer.
Does hydrogen collect at floor level like LPG?
The opposite, and this matters for detector placement. Hydrogen is the lightest substance there is, roughly one fourteenth the density of air, so it rises fast and collects under roofs and in ceiling voids. Detection and ventilation for hydrogen belong at **high** level. A floor-mounted detector will read clean while gas accumulates over your head.
What is hydrogen embrittlement, and does it affect cylinders?
Hydrogen can diffuse into some steels and reduce their ductility over time, particularly at high pressure. It is why hydrogen service uses specified materials rather than whatever is to hand, and why cylinders, valves and pipework for hydrogen must not be substituted from another gas service. Use only equipment rated for hydrogen.
Can I use the same regulator as for other gases?
No. Hydrogen uses dedicated, hydrogen-rated equipment with a left-hand thread connection, which exists precisely to stop it being coupled to the wrong service. Never adapt, never force a fitting, and never use oil or grease anywhere in the system.
How should a hydrogen fire be tackled?
By stopping the flow, not by putting the flame out. Extinguishing a hydrogen flame while gas keeps escaping produces an unignited flammable cloud that will find another ignition source and deflagrate. Isolate the supply if it is safe to do so, cool surrounding cylinders from a protected position, and let the flame burn out under control.
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