Hydrogen

1Identification

Name

Hydrogen

IUPAC name

molecular hydrogen

CAS number

1333-74-0

Molecular formula

H2

Molecular weight

2.016 g/mol

InChIKey

UFHFLCQGNIYNRP-UHFFFAOYSA-N

SMILES

[HH]

PubChem CID

783

Synonyms

Hydrogen, Molecular hydrogen, Dihydrogen, Protium, hydrogen-1, Hydrogen atoms, RefChem:389053, H, Atomic hydrogen, Hydrogen gas, H2, Hydrogen in Steel, 1g/piece, 1-Butanol, titanium(4+) salt, monohydrate, homopolymer (9CI), Hydrogen, atomic

Recommended uses

• Used in welding (oxy-hydrogen and autogenous), petroleum refining, and as a coolant; Used to hydrogenate oils and other organic compounds and to reduce metal oxides; [Merck Index]
  Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
• Petroleum Production and Refining [Category: Industry] Gas Welding and Cutting [Category: Weld]
  Haz-Map, Information on Hazardous Chemicals and Occupational Diseases
• In oxy-hydrogen blowpipe (welding) and limelight; autogenous welding of steel and other metals; manufacturing ammonia, synthetic methanol, HCl, NH3; hydrogenation of oils, fats, naphthalene, phenol; in balloons and airships; in metallurgy to reduce oxides to metals; in petroleum refining; in thermonuclear reactions (ionizes to form protons, deuterons (D) or tritons (T).
  Hazardous Substances Data Bank (HSDB)
• Other Insulators Fuel agents Fuel Reducing agent Catalyst Not Known or Reasonably Ascertainable Processing aids, specific to petroleum production Intermediate
  EPA Chemical Data Reporting (CDR)
• Not Known or Reasonably Ascertainable Fuel agents
  EPA Chemical Data Reporting (CDR)

Use categories: Food additives

Description

• Hydrogen is a colorless, odorless gas. It is easily ignited. Once ignited it burns with a pale blue, almost invisible flame. The vapors are lighter than air. It is flammable over a wide range of vapor/air concentrations. Hydrogen is not toxic but is a simple asphyxiate by the displacement of oxygen in the air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. Hydrogen is used to make other chemicals and in oxyhydrogen welding and cutting.
  CAMEO Chemicals
• Hydrogen, refrigerated liquid (cryogenic liquid) appears as a colorless very cold liquid shipped in special heavily insulated containers. Boils at -442 °F. Contact causes severe frostbite. Hydrogen gas at normal temperatures is lighter than air but until vapors boiling off from the liquid warm up they are heavier than air. Very easily ignited. Burns with a pale blue, almost invisible flame. A leak could be either a vapor or a liquid leak. The container is designed to vent the vapor as it is boils off. Under prolonged exposure to intense heat the containers may rupture violently and rocket.
  CAMEO Chemicals
• Dihydrogen is an elemental molecule consisting of two hydrogens joined by a single bond. It has a role as an electron donor, an antioxidant, a fuel, a human metabolite and a member of food packaging gas. It is a gas molecular entity, an elemental molecule and an elemental hydrogen.
  ChEBI

2Hazard identification

Signal word

Danger

Pictograms

GHS02, GHS04

Classification source

Regulation (EC) No 1272/2008 of the European Parliament and of the Council

Precautionary statements

Other reported classifications

6 classification records exist across sources. Differences usually reflect purity, physical form or impurities.

NFPA 704 rating

• 0 - Materials that, under emergency conditions, would offer no hazard beyond that of ordinary combustible materials.
  Hazardous Substances Data Bank (HSDB)
• 4 - Materials that rapidly or completely vaporize at atmospheric pressure and normal ambient temperature or that are readily dispersed in air and burn readily.
  Hazardous Substances Data Bank (HSDB)
• 0 - Materials that in themselves are normally stable, even under fire conditions.
  Hazardous Substances Data Bank (HSDB)

Health hazards

• Excerpt from ERG Guide 115 [Gases - Flammable (Including Refrigerated Liquids)]: Vapors may cause dizziness or asphyxiation without warning, especially when in closed or confined areas. Some may be irritating if inhaled at high concentrations. Contact with gas, liquefied gas or cryogenic liquids may cause burns, severe injury and/or frostbite. Fire may produce irritating and/or toxic gases. (ERG, 2024)
  CAMEO Chemicals
• If atmosphere does not contain enough oxygen, inhalation can cause dizziness, unconsciousness, or even death. Contact of liquid with eyes or skin causes freezing similar to burn. (USCG, 1999)
  CAMEO Chemicals
• · Vapors may cause dizziness or asphyxiation without warning, especially when in closed or confined areas. · Some may be irritating if inhaled at high concentrations. · Contact with gas, liquefied gas or cryogenic liquids may cause burns, severe injury and/or frostbite. · Fire may produce irritating and/or toxic gases.
  Emergency Response Guidebook (ERG)

Fire hazards

• Excerpt from ERG Guide 115 [Gases - Flammable (Including Refrigerated Liquids)]: EXTREMELY FLAMMABLE. Will be easily ignited by heat, sparks or flames. Will form explosive mixtures with air. Vapors from liquefied gas are initially heavier than air and spread along ground. CAUTION: Hydrogen (UN1049), Deuterium (UN1957), Hydrogen, refrigerated liquid (UN1966), Methane (UN1971) and Hydrogen and Methane mixture, compressed (UN2034) are lighter than air and will rise. Hydrogen and Deuterium fires are difficult to detect since they burn with an invisible flame. Use an alternate method of detection (thermal camera, broom handle, etc.) Vapors may travel to source of ignition and flash back.
  CAMEO Chemicals
• Behavior in Fire: Burns with an almost invisible flame. (USCG, 1999)
  CAMEO Chemicals
• · EXTREMELY FLAMMABLE. · Will be easily ignited by heat, sparks or flames. · Will form explosive mixtures with air. · Vapors from liquefied gas are initially heavier than air and spread along ground. CAUTION: Hydrogen (UN1049), Deuterium (UN1957), Hydrogen, refrigerated liquid (UN1966), Methane (UN1971) and Hydrogen and Methane mixture, compressed (UN2034) are lighter than air and will rise. Hydrogen and Deuterium fires are difficult to detect since they burn with an invisible flame. Use an alternate method of detection (thermal camera, broom handle, etc.) · Vapors may travel to source of ignition and flash back.
  Emergency Response Guidebook (ERG)

Hazards summary

• Simple asphyxiant; Contact with evaporating liquid can cause frostbite; [HSDB]
  Haz-Map, Information on Hazardous Chemicals and Occupational Diseases

3Composition / information on ingredients

This page describes the pure substance. Commercial products may be solutions or mixtures. Check Section 3 of your supplier's SDS for concentrations and other ingredients.

4First-aid measures

• Excerpt from ERG Guide 115 [Gases - Flammable (Including Refrigerated Liquids)]: Refer to the "General First Aid" section. Specific First Aid: Clothing frozen to the skin should be thawed before being removed. In case of contact with liquefied gas, only medical personnel should attempt thawing frosted parts. In case of burns, immediately cool affected skin for as long as possible with cold water. Do not remove clothing if adhering to skin. (ERG, 2024)
  CAMEO Chemicals
• The only effect of exposure to liquid hydrogen is that caused by its unusually low temperature and its action as a simple asphyxiant. INHALATION: if victim is unconscious (due to oxygen deficiency), move him to fresh air and apply resuscitation methods; call physician. EYES: treat for frostbite. SKIN: treat for frostbite; soak in lukewarm water; get medical attention if burn is severe. (USCG, 1999)
  CAMEO Chemicals
• General First Aid: · Call 911 or emergency medical service. · Ensure that medical personnel are aware of the material(s) involved, take precautions to protect themselves and avoid contamination. · Move victim to fresh air if it can be done safely. · Administer oxygen if breathing is difficult. · If victim is not breathing: -- DO NOT perform mouth-to-mouth resuscitation; the victim may have ingested or inhaled the substance. -- If equipped and pulse detected, wash face and mouth, then give artificial respiration using a proper respiratory medical device (bag-valve mask, pocket mask equipped with a one-way valve or other device).
  Emergency Response Guidebook (ERG)

Symptoms of exposure

• Dizziness. Headache. Lethargy. Suffocation.
  ILO-WHO International Chemical Safety Cards (ICSCs)
• ON CONTACT WITH GAS: FROSTBITE.
  ILO-WHO International Chemical Safety Cards (ICSCs)

5Fire-fighting measures

• To fight fire, stop flow of gas.
  Hazardous Substances Data Bank (HSDB)
• Approach fire with caution as high-temperature flame is practically invisible. Stop flow of gas before extinguishing fire. Use water spray to keep fire-exposed containers cool. Use flooding quantities of water as fog or spray. /Hydrogen, refrigerated liquid/
  Hazardous Substances Data Bank (HSDB)
• Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide. Wear self-contained breathing apparatus for firefighting if necessary. Use water spray to cool unopened containers.
  Hazardous Substances Data Bank (HSDB)

6Accidental release measures

Isolation and evacuation

• Excerpt from ERG Guide 115 [Gases - Flammable (Including Refrigerated Liquids)]: IMMEDIATE PRECAUTIONARY MEASURE: Isolate spill or leak area for at least 100 meters (330 feet) in all directions. LARGE SPILL: Consider initial downwind evacuation for at least 800 meters (1/2 mile). FIRE: If tank, rail tank car or highway tank is involved in a fire, ISOLATE for 1600 meters (1 mile) in all directions; also, consider initial evacuation for 1600 meters (1 mile) in all directions.
  CAMEO Chemicals
• Immediate precautionary measure · Isolate spill or leak area for at least 100 meters (330 feet) in all directions. Large Spill · Consider initial downwind evacuation for at least 800 meters (1/2 mile). Fire · If tank, rail tank car or highway tank is involved in a fire, ISOLATE for 1600 meters (1 mile) in all directions; also, consider initial evacuation for 1600 meters (1 mile) in all directions. · In fires involving Liquefied Petroleum Gases (LPG) (UN1075), Butane (UN1011), Butylene (UN1012), Isobutylene (UN1055), Propylene (UN1077), Isobutane (UN1969), and Propane (UN1978), also refer to the "BLEVE - Safety Precautions" section.
  Emergency Response Guidebook (ERG)

Spill cleanup

• Evacuate danger area! Consult an expert! Ventilation. Remove all ignition sources. Remove vapour with fine water spray.
  ILO-WHO International Chemical Safety Cards (ICSCs)
• ACCIDENTAL RELEASE MEASURES: Personal precautions, protective equipment and emergency procedures: Avoid breathing vapors, mist or gas. Ensure adequate ventilation. Remove all sources of ignition. Evacuate personnel to safe areas. Beware of vapors accumulating to form explosive concentrations. Vapors can accumulate in low areas. Environmental precautions: Prevent further leakage or spillage if safe to do so. Do not let product enter drains. Methods and materials for containment and cleaning up: Clean up promptly by sweeping or vacuum.
  Hazardous Substances Data Bank (HSDB)
• Eliminate all ignition sources. Approach release from upwind. Stop or control the leak, if this can be done without undue risk. Use water spray to disperse vapors and protect personnel. /Hydrogen, refrigerated liquid/
  Hazardous Substances Data Bank (HSDB)

7Handling and storage

• Fireproof. Cool. Ventilation along the floor and ceiling. Separated from oxidizing materials.
  ILO-WHO International Chemical Safety Cards (ICSCs)
• Store in a cool, dry, well-ventilated location. Outside or detached storage is preferred. Isolate from oxygen, halogens, other oxidizing materials. /Hydrogen, refrigerated liquid/
  Hazardous Substances Data Bank (HSDB)
• A safe storage method for hydrogen for possible use as automotive fuel involves the use of metal hydrides from which the hydrogen is released at specified temperatures. Iron titanium hydride has been found the most satisfactory.
  Hazardous Substances Data Bank (HSDB)
• Keep container tightly closed in a dry and well-ventilated place. Contents under pressure. Storage class (TRGS 510): Gases
  Hazardous Substances Data Bank (HSDB)

8Exposure controls / personal protection

Personal protective equipment

• Excerpt from ERG Guide 115 [Gases - Flammable (Including Refrigerated Liquids)]: Wear positive pressure self-contained breathing apparatus (SCBA). Structural firefighters' protective clothing provides thermal protection but only limited chemical protection. Always wear thermal protective clothing when handling refrigerated/cryogenic liquids. (ERG, 2024)
  CAMEO Chemicals
• Safety goggles or face shield; insulated gloves and long sleeves; cuffless trousers worn outside boots or over high-top shoes to shed spilled liquid; self-contained breathing apparatus containing air (never use oxygen). (USCG, 1999)
  CAMEO Chemicals
• Eye/face protection: Face shield and safety glasses. Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
  Hazardous Substances Data Bank (HSDB)
• Wear special protective clothing and positive pressure self-contained breathing apparatus. /Hydrogen, refrigerated liquid/
  Hazardous Substances Data Bank (HSDB)

9Physical and chemical properties

10Stability and reactivity

Reactivity

• Finely divided platinum and some other metals will cause a mixture of hydrogen and oxygen to explode at ordinary temperatures. If a jet of hydrogen in air impinges on platinum black the metal surface gets hot enough to ignite the gases, [Mellor 1:325(1946-1947)]. Explosive reactions occur upon ignition of mixtures of nitrogen trifluoride with good reducing agents such as ammonia, hydrogen, hydrogen sulfide or methane. Mixtures of hydrogen, carbon monoxide, or methane and oxygen difluoride are exploded when a spark is discharged, [Mellor 2, Supp. 1:192(1956)]. An explosion occurred upon heating 1'-pentol and 1''-pentol under hydrogen pressure.
  CAMEO Chemicals
• Highly flammable.
  CAMEO Chemicals

Incompatible materials and hazardous reactions

• Release of hydrogen @ 47.5 bar into a vented 17.5-l chromium-plated sphere caused explosive ignition. /Hydrogen/
  Hazardous Substances Data Bank (HSDB)
• Hydrogen ignites in bromine fluoride at ambient temp.
  Hazardous Substances Data Bank (HSDB)
• Mixtures of iodine heptafluoride with hydrogen explode on heating or sparking.
  Hazardous Substances Data Bank (HSDB)

Chemical stability

• Stable under recommended storage conditions.
  Hazardous Substances Data Bank (HSDB)

11Toxicological information

Short-term exposure effects

• Asphyxiation. Exposure to cold gas could cause frostbite.
  ILO-WHO International Chemical Safety Cards (ICSCs)

12Ecological information

Not available in the public sources we compile. Check Section 12 of the supplier's SDS.

13Disposal considerations

• SRP: Recycle any unused portion of the material for its approved use or return it to the manufacturer or supplier. Ultimate disposal of the chemical must consider: the material's impact on air quality; potential migration in air, soil or water; effects on animal, aquatic and plant life; and conformance with environmental and public health regulations. If it is possible or reasonable use an alternative chemical product with less inherent propensity for occupational harm/injury/toxicity or environmental contamination.
  Hazardous Substances Data Bank (HSDB)
• Product: Contact a licensed professional waste disposal service to dispose of this material. Burn in a chemical incinerator equipped with an afterburner and scrubber but exert extra care in igniting as this material is highly flammable. Offer surplus and non-recyclable solutions to a licensed disposal company. Contaminated packaging: Dispose of as unused product
  Hazardous Substances Data Bank (HSDB)

14Transport information

UN numbers: UN 1966, UN 1049, UN 1957, UN 1971

Shipping name

• UN 1966; Hydrogen, refrigerated liquid (cryogenic liquid)
  Hazardous Substances Data Bank (HSDB)
• UN 1049; Hydrogen, compressed
  Hazardous Substances Data Bank (HSDB)

DOT hazard class

• Hydrogen, compressed
  US Code of Federal Regulations, Hazardous Materials, 49 CFR Part 172
• UN1049
  US Code of Federal Regulations, Hazardous Materials, 49 CFR Part 172
• Div 2.1 Flammable gas (49 eCFR § 173.115)
  US Code of Federal Regulations, Hazardous Materials, 49 CFR Part 172

DOT label

• Flammable Gas
  CAMEO Chemicals

UN classification

• UN Hazard Class: 2.1
  ILO-WHO International Chemical Safety Cards (ICSCs)

Emergency Response Guidebook

• 1966 115
  Emergency Response Guidebook (ERG)
• 1049 115
  Emergency Response Guidebook (ERG)

How DOT hazard classes work →

15Regulatory information

No specific US regulatory listings found in our sources. Check Section 15 of your supplier's SDS for TSCA, SARA 313, CERCLA, Prop 65 and state listings.

Overview of SDS regulations (OSHA HazCom, WHMIS, REACH/CLP) →

16Other information

Compiled from PubChem CID 783 and the sources it aggregates (attributed inline). Data retrieved 2026-10-12. This summary describes the pure substance and is not a supplier SDS.