Many gases have toxic properties, which are often assessed using the LC50 (median lethal concentration) measure. In the United States, many of these gases have been assigned an NFPA 704 health rating of 4 (may be fatal) or 3 (may cause serious or permanent injury), and/or exposure limits (TLV, TWA or STEL) determined by the ACGIH professional association. Some, but by no means all, toxic gases are detectable by odor, which can serve as a warning. Among the best known toxic gases are carbon monoxide, chlorine, nitrogen dioxide and phosgene.
Materials that, under emergency conditions, can cause serious or permanent injury are given a Health Hazard rating of 3. Their acute inhalation toxicity corresponds to those vapors or gases having LC50 values greater than 1,000 ppm but less than or equal to 3,000 ppm. Materials that, under emergency conditions, can be lethal are given a Health Hazard rating of 4. Their acute inhalation toxicity corresponds to those vapors or gases having LC50 values less than or equal to 1,000 ppm.
| Chemical name[3] | Chemical formula | CAS number | NIOSH IDLH in ppm | OSHA PEL / NIOSH REL / ACGIH TLV[4] | NFPA 704 Health Rating | NFPA 704 Special Hazard Rating | Additional Notes[5] | |
|---|---|---|---|---|---|---|---|---|
| Arsenic pentafluoride | AsF5 | 7784-36-3 | 5 | NIOSH PEL TWA 0.001 ppm; REL Ceiling 0.0002 ppm(15-min) | 4 | |||
| Arsine | AsH3 | 7784-42-1 | 3 | NIOSH REL (C)(15min): 0.002 mg/m3; OSHA PEL: 0.05 ppm; ACGIH (2006) TWA-TLV 0.05ppm | 4 | LC50: 120 ppm(rat, 10 min) | ||
| Bis(trifluoromethyl)peroxide | C2F6O2 | 927-84-4 | 10 | |||||
| Boron tribromide[6] | BBr3 | 10294-33-4 | 50 | ACGIH (1990) / PEL Ceiling limit 1ppm; AEGL - 1: 0.33 ppm, AEGL - 2: 1.7 ppm, AEGL - 3: 5 ppm | 3 | |||
| Boron trichloride[7] | BCl3 | 10294-34-5 | 25 | No exposure limits have established; 2500 (TQ) | 4 | LC50: 2541 ppm (rat, 1 h)[8] | ||
| Boron trifluoride | BF3 | 7637-07-2 | 25 | OSHA, ACGIH (1962) 1ppm ceiling | 4 | LC50: 436 ppm (4 h) | ||
| Bromine | Br2 | 7726-95-6 | 3 | OSHA PEL 8-hr TWA: 0.1 ppm; ACGIH (1991) STEL-TLV 0.3ppm | 3 | OX | LC50: 174 ppm(mice) Odor threshold: <0.01 ppm | |
| Bromine chloride | BrCl | 13863-41-7 | 1500 (TQ) | 3 | OX | |||
| Bromomethane | CH3Br | 74-83-9 | 250 | NIOSH PEL 20 ppm | 3 | LC50: 302 ppm (Rat, 8 h)[9] | ||
| Carbon monoxide | CO | 630-08-0 | 1,200 (moderately toxic) | ACGIH (1989) TWA TLV 25ppm; NIOSH 35ppm; NIOSH 200ppm Ceiling limit | 3 | LC50: 4600/5000 ppm[10] | ||
| Chlorine | Cl2 | 7782-50-5 | 10 | ACGIH (1986) STEL-TLV 1ppm | 3 | OX | Odor threshold 1ppm, LC50: 433(10 min), 250 (30 min) | |
| Chlorine pentafluoride | ClF5 | 13637-63-3 | AEGL - 2: 0.33 ppm;AEGL - 3: 2.7 ppm | LC50: 194 ppm(Rat) | ||||
| Chlorine trifluoride | ClF3 | 7790-91-2 | 12 | ACGIH (1979) Ceiling limit 0.1ppm | 4 | inadequate odor, LC50: 95 ppm (Rat, 4 h) | ||
| Chloropicrin[11] | CCl3NO2 | 76-06-2 | 2 | ACGIH (1990) TWA-TLV 0.1ppm | 4 | LC50: 9.7 ppm (Mouse, 4 h) | ||
| Cyanogen | C2N2 | 460-19-5 | ACGIH (1966) TWA-TLV 10ppm | 4 | ||||
| Cyanogen chloride | CNCl | 506-77-4 | ACGIH (1977) ceiling limit 0.3ppm | 4 | ||||
| Diazomethane | CH2N2 | 334-88-3 | 2 | ACGIH (1970) TWA-TLV 0.2ppm | 4 | LC50: 175 ppm (Cat, 10 min) | ||
| Diborane | B2H6 | 19287-45-7 | 15 | ACGIH (1990) TWA-TLV 0.1ppm | 4 | inadequate odor, LC50: 40 ppm (Rat, 4 h) | ||
| Dichloroacetylene[12] | C2Cl2 | 7572-29-4 | NIOSH REL 0.1 ppm Ceiling | |||||
| Dichlorosilane | H2Cl2Si | 4109-96-0 | 2500 (TQ) | 4 | LC50: 1785-2092 ppm | |||
| Dimethylmercury | HgC2H6 | 593-74-8 | 4 | |||||
| Ethylene oxide (anhydrous) | C2H4O | 75-21-8 | 800 | REL TWA<0.1 ppm 5 ppm Ceiling | 3 | LC50: 90 mg/L (fish, 24 h) | ||
| Fluorine | F2 | 7782-41-4 | ACGIH (1970) STEL-TLV 2ppm | 4 | OX | odor threshold 20ppb | ||
| Formaldehyde (anhydrous) | CH2O | 50-00-0 | 20 | NIOSH REL 0.016 ppm Ceiling limit 0.1ppm | 3 | LC50: 333 ppm(mouse, 2 h) | ||
| Germane | GeH4 | 7782-65-2 | NIOSH REL 0.2 ppm | 4 | LC50: 440 ppm (mice 2 h) | |||
| Hydrogen azide | HN3 | 7782-79-8 | NIOSH REL: 0.1 ppm Ceiling | 4 | ||||
| Hydrogen cyanide | HCN | 74-90-8 | 50 | PEL TWA 10 ppm; REL ST 4.7 ppm | 4 | LC50: 503 ppm(Rat, 5 min) | ||
| Hydrogen fluoride | HF | 7664-39-3 | 30 | PEL TWA 3 ppm;REL TWA 3 ppm (2.5 mg/m³)TWA 3 ppm; | 4 | POI | LCLo 313 ppm (rabbit, 7 hr) | |
| Hydrogen selenide | H2Se | 7783-07-5 | 1 | ACGIH (1990) TWA-TLV 0.05ppm | 4 | LC50: 1.8 ppm(G.Pig,4 h) | ||
| Hydrogen sulfide | H2S | 7783-06-4 | 100 | NIOSH PEL: Ceiling 20 ppm; REL Ceiling 10 ppm; ACGIH (1990) STEL-TLV 15ppm | 4 | LC50: 444 ppm, Odor Threshold 0.3 ppm | ||
| Hydrogen telluride | H2Te | 7783-09-7 | 4 | |||||
| Nickel tetracarbonyl | Ni(CO)4 | 13463-39-3 | 2 | NIOSH TWA PEL 0.001 ppm; ACGIH (1980) TWA-TLV 0.05ppm | 4 | LC50: 9.642 ppm[13] | ||
| Nitrogen dioxide | NO2 | 10102-44-0 | 13 | NIOSH PEL Ceiling 5 ppm; REL ST 1 ppm | 3 | OX | odor threshold 4 ppm; LC50: 99 ppm (mice, 1 h) | |
| Osmium tetroxide | OsO4 | 20816-12-0 | 0.001 | NIOSH PEL TWA 0.0002 ppm; REL TWA 0.0002 ppm, ST 0.0006 ppm | 3 | OX | LC50: 40 ppm (rats, 4 h); odor threshold: 0.0019 ppm | |
| Oxygen difluoride | OF2 | 7783-41-7 | 0.5 | NIOSH PEL TWA 0.05 ppm; REL Ceiling 0.05 ppm; ACGIH (1983) ceiling limit 0.05ppm | 4 | OX | Odor Threshold: 0.5 ppm; LC50: 26.067 ppm (Rhesus monkeys, 1 h) | |
| Perchloryl fluoride | ClFO3 | 7616-94-6 | 100 | NIOSH PEL TWA 3 ppm; REL TWA 3 ppm, ST 6 ppm; ACGIH (1962) STEL-TLV 6ppm | 3 | OX | LC50: 385 ppm (Rat, 4 h) | |
| Perfluoroisobutylene | C4F8 | 382-21-8 | 1.2 | LC50: 17 ppm (Rat, 10 min) | ||||
| Phosgene | CCl2O | 75-44-5 | 2 | NIOSH PEL TWA 0.1 ppm; REL TWA 0.1 ppm, Ceiling 0.2 ppm; ACGIH (1992) TWA-TLV 0.1ppm | 4 | Odor Threshold 0.5 to 1.5 ppm | ||
| Phosphine | PH3 | 7803-51-2 | 50 | NIOSH 0.3ppm time weighted average; ACGIH (1992) STEL-TLV 1ppm | 4 | LC50: 0.44 ppm (Rat, 4 h) | ||
| Phosphorus pentafluoride[14] | PF5 | 7647-19-0 | 25 | TLV - TWA 0.25 ppm ACGIH & OSHA | 4 | |||
| Selenium hexafluoride | SeF6 | 7783-79-1 | 2 | OSHA PEL, NIOSH REL, ACGIH (1992) TWA-TLV 0.05ppm | 3 | |||
| Silicon tetrachloride[15] | SiCl4 | 10026-04-7 | OSHA PEL, NIOSH REL 5 ppm, ACGIH TLV 2 ppm | 3 | LC50: 8000 ppm (Rat, 4 h) Odor Threshold: 1 - 5 ppm | |||
| Silicon tetrafluoride | SiF4 | 7783-61-1 | 3 | LC50: 922 ppm (Rats, 1 h) | ||||
| Stibine[16] | H3Sb | 7803-52-3 | 5 | OSHA PEL/NIOSH REL/ACGIH TLV: 0.1 ppm | 4 | |||
| Disulfur decafluoride | S2F10 | 5714-22-7 | 1 | ACGIH (1962) ceiling limit 0.01ppm | 4 | OX | LC50: 2 ppm (Rat, 10min) | |
| Sulfur tetrafluoride | SF4 | 7783-60-0 | OSHA PEL/NIOSH REL/ACGIH (1992) ceiling limit 0.1ppm[17] | 3 | LC50: 40 ppm (Rat, 1 h) | |||
| Tellurium hexafluoride | TeF6 | 7783-80-4 | 1 | NIOSH REL/ACGIH (1992) TWA-TLV 0.02ppm | ||||
| Tetraethyl pyrophosphate | C8H20O7P2 | 107-49-3 | 5 | ACGIH (2006) TWA-TLV 0.01 mg/cubic meter | 4 | |||
| Sulfotep | C8H20O5P2S2 | 3689-24-5 | 10 | NIOSH PEL TWA 0.2 ppm | 4 | LC50: 38 ppm (Rat, 4h) | ||
| Trifluoroacetyl chloride | C2ClF3O | 354-32-5 | ||||||
| Tungsten hexafluoride[18] | WF6 | 7783-82-6 | OSHA PEL TWA 2.5 ppm, ACGIH TLV TWA 3 ppm | 3 | LC50: 218 ppm (Rat, 1 h) |