Identifiers for search
| Name | Ammonia |
| Formula | NH₃ |
| IUPAC name | azane |
| CAS number | 7664-41-7 |
| EC number | 231-635-3 |
| UN number | 1005 — Ammonia, anhydrous |
| Transport class (ADR/RID) | 2.3 (Toxic gases) |
| PubChem CID | 222 |
| Synonyms | Anhydrous ammonia, Aqua ammonia, Aqueous ammonia [Note: Often used in an aqueous solution.] |
Physical & chemical properties
| Molar mass | 17.03 g/mol |
| Boiling point (1 atm) | -33.4 °C |
| Melting point | -77.7 °C |
| Critical temperature | 132.4 °C |
| Critical pressure | 112.8 bar |
| Vapour pressure | 8.574 bar at 20 °C |
| Gas density | 0.7714 kg/m³ (0 °C, 1013 mbar) |
| Relative density (air = 1) | 0.6 |
| Solubility in water | 531 g/l at 20 °C |
| Appearance | gas liquefied under pressure, colourless, pungent suffocating odour |
| Odour | pungent suffocating odour |
| 1 ppm at 20 °C | 0.708 mg/m³ |
Behaviour with temperature and pressure
Boiling point -33.4 °C at 1 atm: a liquefied gas under its own vapour pressure in cylinders. Critical point 132.4 °C / 112.8 bar: below this temperature it can be stored as a liquid; cylinder pressure then equals the vapour pressure. Vapour pressure ≈ 8.574 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 0.6 (air = 1): lighter than air — rises and collects under ceilings; place sensors high. Conversion at 20 °C, 1013 mbar: 1 ppm = 0.708 mg/m³; NDIR reads partial pressure, so readings scale with absolute pressure (value = reading × P/1013) and must be pressure-compensated.
// Flammable gas., Ammonia gas burns only at high concentrations, high temperature and a strong energy source. Without heat input the flame extinguishes immediately., Freely soluble in water., Aqueous solution reacts alkaline., Gas is lighter than air., Acute or chronic health hazards result from the substance.
Hazards & safety
NFPA 704
health · flammability · instability · special
GHS / CLP pictograms
| Hazard class | toxic + corrosive + flammable |
| GHS signal word | Danger |
| CLP classification | Flammable gases, Category 2; H221 Gases under pressure, liquefied gas; H280 Acute toxicity, Category 3, inhalation; H331 Skin corrosion, Category 1B; H314 Serious eye damage, Category 1; H318 Hazardous to the aquatic environment, Acute Category 1; H400 Hazardous to the aquatic environment, Chronic Category 2; H411 |
| Hazard statements | H221: Flammable gas. H280: Contains gas under pressure; may explode if heated. H314: Causes severe skin burns and eye damage. H331: Toxic if inhaled. H410: Very toxic to aquatic life with long lasting effects. EUH071: Corrosive to the respiratory tract. |
| Lower / upper explosion limit | 14 vol% / 32.5 vol% |
| Auto-ignition temperature | 630 °C · T1 · group IIA |
| Seveso III named substance | yes |
Exposure limits
| EU indicative OELV (8 h TWA) | 20 ppm · 14 mg/m³ — Directive 2000/39/EC |
| EU IOELV short-term (15 min) | 50.85 ppm · 36 mg/m³ |
| Germany AGW (TRGS 900) | 20 ppm · 14 mg/m³ |
| Netherlands | wettelijke grenswaarde per Arboregeling bijlage XIII — SER grenswaarden database |
| NIOSH REL (USA) | TWA 25 ppm (18 mg/m3) ST 35 ppm (27 mg/m3) |
| OSHA PEL (USA) | TWA 50 ppm (35 mg/m3) See Appendix G |
| IDLH | 300 ppm |
// 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
Corrosive alkaline gas: severe eye and airway irritation from 20–30 ppm, intolerable ~300 ppm (IDLH), laryngeal/pulmonary oedema and death from ~1700 ppm. Liquid splash causes frostbite plus chemical burn. Odour threshold ~5 ppm gives warning.
GESTIS main toxic effects: Acute:
Severely irritative/corrosive effects to the eyes, respiratory tract and skin,
danger of severe damage to the eyes and respiratory tract
Chronic:
Chronic respiratory irritation/respiratory complaints
Recommended monitoring
- Electrochemical for 0–100 ppm workplace; NDIR (10.5 µm) or laser for refrigeration plants (0–1 vol%) and process/agricultural monitoring where EC cells die from continuous exposure.
- Alarms: 20 ppm (IOELV) pre-alarm, 50 ppm main in refrigeration machine rooms (EN 378 requires detection at 500 ppm max); sensors at ceiling (lighter than air).
Climate & atmosphere
| GWP₁₀₀ — IPCC AR6 | — |
| GWP₁₀₀ — IPCC AR4 | — |
| GWP used in Reg. (EU) 2024/573 | not listed |
| Atmospheric lifetime | — |
| Ozone depletion potential | 0 |
| Main IR absorption band (NDIR) | 10.3–10.7 µm (ν₂ umbrella, 932/968 cm⁻¹); 6.1 µm (ν₄); 3.0 µm (N–H stretch) |
Regulation windows
- Workplace: EU IOELV 20 ppm / STEL 50 ppm (Dir. 2000/39/EC)
- EN 378 — refrigerating systems: detectors mandatory in machinery rooms
- IED / NEC Directive 2016/2284 — agricultural NH₃ emission ceilings
- Seveso III — named substance (50 t / 200 t tiers)
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Other gases
Sources
- https://gestis-database.dguv.de/data?name=001100
- https://www.cdc.gov/niosh/npg/npgd0028.html
- https://pubchem.ncbi.nlm.nih.gov/compound/222
- 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)
- 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.