Identifiers for search
| Name | Nitrous oxide |
| Formula | N₂O |
| IUPAC name | nitrous oxide |
| CAS number | 10024-97-2 |
| EC number | 233-032-0 |
| UN number | 1070 — Nitrous oxide |
| Transport class (ADR/RID) | 2.2 (Non-flammable, non-toxic gases) |
| PubChem CID | 948 |
| Synonyms | Dinitrogen monoxide, Hyponitrous acid anhydride, Laughing gas |
Physical & chemical properties
| Molar mass | 44.01 g/mol |
| Boiling point (1 atm) | -88.5 °C |
| Melting point | -90.8 °C |
| Critical temperature | 36.4 °C |
| Critical pressure | 72.45 bar |
| Vapour pressure | 50.8 bar at 20 °C |
| Gas density | 1.9781 kg/m³ (0 °C, 1013 mbar) |
| Relative density (air = 1) | 1.53 |
| Solubility in water | 1,5 g/l at 15 °C |
| Appearance | gas liquefied under pressure, colourless, sweetish odour |
| Odour | sweetish odour |
| 1 ppm at 20 °C | 1.83 mg/m³ |
Behaviour with temperature and pressure
Boiling point -88.5 °C at 1 atm: a gas at all normal conditions. Critical point 36.4 °C / 72.45 bar: below this temperature it can be stored as a liquid; cylinder pressure then equals the vapour pressure. Vapour pressure ≈ 50.8 bar at 20 °C — this is the pressure inside a cylinder or a switchgear compartment at that temperature, and it rises steeply with temperature (Clausius–Clapeyron). Relative density 1.53 (air = 1): heavier than air — accumulates in pits, cable basements and at floor level; place sensors low. Conversion at 20 °C, 1013 mbar: 1 ppm = 1.83 mg/m³; NDIR reads partial pressure, so readings scale with absolute pressure (value = reading × P/1013) and must be pressure-compensated.
// Oxidizing gas., The substance itself does not burn, but in contact with combustible substances it increases the risk of fire and can fuel any existing fire substantially., Like oxygen, nitrous oxide maintains a fire involving combustible material like wood or sulfur., Only slightly soluble in water., Gas is heavier than air., Acute or chronic health hazards result from the substance.
Hazards & safety
NFPA 704
health · flammability · instability · special
GHS / CLP pictograms
| Hazard class | oxidizer; anaesthetic (toxic at chronic low ppm); greenhouse gas |
| GHS signal word | Danger |
| CLP classification | Oxidising gases, Category 1; H270 Gases under pressure, liquefied gas; H280 Specific Target Organ Toxicity (single exposure), Category 3; H336 Reproductive toxicity, Category 1B; H360Df Specific Target Organ Toxicity (repeated exposure), Category 1; H372 Hazardous to the ozone layer, Category 1; H420 |
| Hazard statements | H270: May cause or intensify fire; oxidiser. H280: Contains gas under pressure; may explode if heated. H336: May cause drowsiness or dizziness. H360Df: May damage the unborn child. Suspected of damaging fertility. H372: Causes damage to organs through prolonged or repeated exposure. H420: Harms public health and the environment by destroying ozone in the upperatmosphere |
| Lower / upper explosion limit | non-flammable |
| Auto-ignition temperature | — |
| Seveso III named substance | yes |
Exposure limits
| EU indicative OELV (8 h TWA) | no EU IOELV |
| EU IOELV short-term (15 min) | — |
| Germany AGW (TRGS 900) | 100 ppm · 180 mg/m³ |
| Netherlands | wettelijke grenswaarde per Arboregeling bijlage XIII — SER grenswaarden database |
| NIOSH REL (USA) | TWA 25 ppm (46 mg/m3) (TWA over the time exposed) [*Note: REL for exposure to waste anesthetic gas.] |
| OSHA PEL (USA) | none |
| IDLH | N.D. |
// Limits change: always confirm the current national value before setting an alarm. Values above were read from the EU directives / GESTIS / NIOSH pages listed in Sources.
Effect on people
Anaesthetic gas. Acute: euphoria, dizziness, loss of coordination; high concentrations asphyxiate. Chronic low-level exposure (waste anaesthetic gas) inactivates vitamin B₁₂ → neuropathy, and is linked to reproductive effects — hence the 100 ppm (DE) / 25 ppm (NIOSH) limits.
GESTIS main toxic effects: Acute:
nervous system dysfunction (analgaesic and narcotic effects at high concentrations), haematopoiesis dysfunction (via deactivation of vitamin B12) .
Chronic:
impairment of blood formation, disturbance and damage to the nervous system (neuromyelopathies) [7619, 7748].
Recommended monitoring
- NDIR at 4.5 µm (with CO₂ cross-compensation) for hospital/dental waste-gas monitoring and for process/CEMS (N₂O is an IED and ETS-reported pollutant).
- Alarm/limit: 100 ppm AGW (DE) / 25 ppm NIOSH TWA for anaesthetic use; agriculture and nitric-acid plants report N₂O under IED/ETS.
Climate & atmosphere
| GWP₁₀₀ — IPCC AR6 | 273 |
| GWP₁₀₀ — IPCC AR4 | 298 |
| GWP used in Reg. (EU) 2024/573 | 273 |
| Atmospheric lifetime | 109 years |
| Ozone depletion potential | — |
| Main IR absorption band (NDIR) | 4.5 µm (ν₃, 2224 cm⁻¹); 7.8 µm (ν₁, 1285 cm⁻¹) |
| Note | ODP: N₂O is the dominant ozone-depleting emission of the 21st century (Ravishankara et al. 2009) but has no Montreal-Protocol ODP value assigned. |
Regulation windows
- IED 2024/1785 — N₂O is a reported pollutant (nitric/adipic acid, waste incineration)
- EU ETS — N₂O from nitric acid plants
- Workplace: DE AGW 100 ppm; NIOSH REL 25 ppm (anaesthetic waste gas)
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Other gases
Sources
- https://gestis-database.dguv.de/data?name=004230
- https://www.cdc.gov/niosh/npg/npgd0465.html
- https://pubchem.ncbi.nlm.nih.gov/compound/948
- IPCC AR6 WG1 Ch.7 Supplementary Material, Table 7.SM.7 (https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter07_SM.pdf)
- IPCC AR4 WG1 Ch.2, Table 2.14 (https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-chapter2-1.pdf)
- Regulation (EU) 2024/573, Annex I/III (https://eur-lex.europa.eu/eli/reg/2024/573/oj)
- HITRAN/NIST IR band positions (approximate centre of the strongest band used for NDIR; https://hitran.org, https://webbook.nist.gov)
// Data compiled 2026-09-17 from the listed primary sources; null values were left blank rather than estimated.