List of highly toxic gases

Last updated February 10, 2025

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/PEL, STEL, or REL) 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.

Definitions

Toxic: a chemical that has a median lethal concentration (LC₅₀) in air of more than 200 parts per million (ppm) but not more than 2,000 parts per million by volume of gas or vapor, or more than 2 milligrams per liter but not more than 20 milligrams per liter of mist, fume or dust, when administered by continuous inhalation for 1 hour (or less if death occurs within 1 hour) to albino rats weighing between 200 and 300 grams each.^[1]^[2]
Highly Toxic: a gas that has a LC₅₀ in air of 200 ppm or less.^[2]
NFPA 704: 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.

List

Chemical name ^[3]	Chemical formula	CAS number	NIOSH IDLH (ppm)	OSHA PEL / NIOSH REL / ACGIH TLV ^[4]	NFPA 704 Ratings		LC₅₀ (ppm)^[5]	Odor threshold (ppm)^[5]
Chemical name ^[3]	Chemical formula	CAS number	NIOSH IDLH (ppm)	OSHA PEL / NIOSH REL / ACGIH TLV ^[4]	Health	Special Hazard	LC₅₀ (ppm)^[5]	Odor threshold (ppm)^[5]
Arsenic pentafluoride	AsF₅	7784-36-3	5	NIOSH PEL TWA 0.001 ppm; REL Ceiling 0.0002 ppm (15 min)	4
Arsine ^[4]	AsH₃	7784-42-1	3	NIOSH REL (C) (15 min): 0.002 mg/m³; OSHA PEL: 0.05 ppm; ACGIH (2006) TWA-TLV 0.05 ppm	4		120 (rat, 10 min)
Bis(trifluoromethyl)peroxide	C₂F₆O₂	927-84-4	10
Boron tribromide ^[6]	BBr₃	10294-33-4	50	ACGIH (1990) / PEL Ceiling limit 1 ppm; AEGL-1: 0.33 ppm, AEGL-2: 1.7 ppm, AEGL-3: 5 ppm	3	W
Boron trichloride ^[7]	BCl₃	10294-34-5	25	No exposure limits have established; 2500 (TQ)	4	W	2541 (rat, 1 h)^[8]
Boron trifluoride	BF₃	7637-07-2	25	OSHA, ACGIH (1962) 1 ppm ceiling	4		436 (4 h)^[8]
Bromine	Br₂	7726-95-6	3	OSHA PEL 8-hr TWA: 0.1 ppm; ACGIH (1991) STEL-TLV 0.3 ppm	3	OX	174 (mice)	<0.01
Bromine chloride	BrCl	13863-41-7		1500 (TQ)	3	OX
Bromomethane	CH₃Br	74-83-9	250	NIOSH PEL 20 ppm	3		302 (Rat, 8 h)^[9]
Carbon monoxide	CO	630-08-0	1,200 (moderately toxic)	ACGIH (1989) TWA TLV 25 ppm; NIOSH 35 ppm; NIOSH 200 ppm Ceiling limit	3		4600/5000^[10]
Chlorine	Cl₂	7782-50-5	10	ACGIH (1986) STEL-TLV 1 ppm	3	OX	433 (10 min), 250 (30 min)	1
Chlorine pentafluoride	ClF₅	13637-63-3		AEGL-2: 0.33 ppm, AEGL-3: 2.7 ppm			194 (Rat)
Chlorine trifluoride	ClF₃	7790-91-2	12	ACGIH (1979) Ceiling limit 0.1 ppm	4	W+OX	95 (Rat, 4 h)	Inadequate odor
Chloropicrin ^{[note 1]}	CCl₃NO₂	76-06-2	2	ACGIH (1990) TWA-TLV 0.1 ppm	4		9.7 (Mouse, 4 h)
Cyanogen	C₂N₂	460-19-5		ACGIH (1966) TWA-TLV 10 ppm	4
Cyanogen chloride	CNCl	506-77-4		ACGIH (1977) ceiling limit 0.3 ppm	4
Diazomethane	CH₂N₂	334-88-3	2	ACGIH (1970) TWA-TLV 0.2 ppm	4		175 (Cat, 10 min)
Diborane	B₂H₆	19287-45-7	15	ACGIH (1990) TWA-TLV 0.1 ppm	4	W	40 (Rat, 4 h)	Inadequate odor
Dichloroacetylene ^{[note 2]}	C₂Cl₂	7572-29-4		NIOSH REL 0.1 ppm Ceiling
Dichlorosilane	H₂Cl₂Si	4109-96-0		2500 (TQ)	4	W	1785-2092
Dimethylmercury	HgC₂H₆	593-74-8			4
Ethylene oxide (anhydrous)	C₂H₄O	75-21-8	800	REL TWA <0.1 ppm, 5 ppm Ceiling	3		90 mg/L (fish, 24 h)
Fluorine	F₂	7782-41-4		ACGIH (1970) STEL-TLV 2 ppm	4	OX		20 ppb
Formaldehyde (anhydrous)	CH₂O	50-00-0	20	NIOSH REL 0.016 ppm, Ceiling limit 0.1 ppm	3		333 (mouse, 2 h)
Germane	GeH₄	7782-65-2		NIOSH REL 0.2 ppm	4		440 (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		503 (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	LC_Lo 313 (rabbit, 7 hr)
Hydrogen selenide	H₂Se	7783-07-5	1	ACGIH (1990) TWA-TLV 0.05 ppm	4		1.8 (G.Pig, 47 h)
Hydrogen sulfide	H₂S	7783-06-4	100	NIOSH PEL: Ceiling 20 ppm; REL Ceiling 10 ppm; ACGIH (1990) STEL-TLV 15 ppm	4		444	0.3
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 0.05 ppm	4		9.642^[11]
Nitrogen dioxide	NO₂	10102-44-0	13	NIOSH PEL Ceiling 5 ppm; REL ST 1 ppm	3	OX	99 (mice, 1 h)	4
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	40 (rat, 4 h)	0.0019
Oxygen difluoride	OF₂	7783-41-7	0.5	NIOSH PEL TWA 0.05 ppm; REL Ceiling 0.05 ppm; ACGIH (1983) ceiling limit 0.05 ppm	4	OX	26.067 (Rhesus monkeys, 1 h)	0.5
Perchloryl fluoride	ClFO₃	7616-94-6	100	NIOSH PEL TWA 3 ppm; REL TWA 3 ppm, ST 6 ppm; ACGIH (1962) STEL-TLV 6 ppm	3	OX	385 (Rat, 4 h)
Perfluoroisobutylene	C₄F₈	382-21-8		1.2 ppm			17 (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 0.1 ppm	4			0.5 to 1.5
Phosphine	PH₃	7803-51-2	50	NIOSH 0.3 ppm time weighted average; ACGIH (1992) STEL-TLV 1 ppm	4		0.44 (Rat, 4 h)
Phosphorus pentafluoride ^[12]	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 0.05 ppm	3
Silicon tetrachloride ^[13]	SiCl₄	10026-04-7		OSHA PEL, NIOSH REL 5 ppm; ACGIH TLV 2 ppm	3	W	8000 (Rat, 4 h)	1 - 5
Silicon tetrafluoride	SiF₄	7783-61-1			3	W	922 (Rat, 1 h)
Stibine ^[14]	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 0.01 ppm	4	OX	2 (Rat, 10 min)
Sulfur tetrafluoride	SF₄	7783-60-0		OSHA PEL/NIOSH REL/ACGIH (1992) ceiling limit 0.1 ppm^[15]	3	W	40 (Rat, 1 h)^[15]
Tellurium hexafluoride	TeF₆	7783-80-4	1	NIOSH REL/ACGIH (1992) TWA-TLV 0.02 ppm
Tetraethyl pyrophosphate ^{[note 1]}	C₈H₂₀O₇P₂	107-49-3	5	ACGIH (2006) TWA-TLV 0.01 mg/m³	4
Sulfotep	C₈H₂₀O₅P₂S₂	3689-24-5	10	NIOSH PEL TWA 0.2 ppm	4		38 (Rat, 4 h)
Trifluoroacetyl chloride	C₂ClF₃O	354-32-5
Tungsten hexafluoride ^[16]	WF₆	7783-82-6		OSHA PEL TWA 2.5 ppm; ACGIH TLV TWA 3 ppm	3	W	218 (Rat, 1 h)

Notes

1 2 Decomposes in gaseous form.
↑ Explodes in gaseous form.

References

↑ "California Fire Code California Code of Regulations,Title 24, Part 9, Chapter 2 - Definitions" (PDF).
1 2 "Environmental Health and Radiation Safety Department at the University of Pennsylvania".
↑ "Chemical Name Search". webbook.nist.gov. Retrieved 2021-11-10.
1 2 "CDC - NIOSH Pocket Guide to Chemical Hazards - Arsenic (inorganic compounds, as As)". www.cdc.gov. Retrieved 2021-11-10.
1 2 "Principles for the safe handling and distribution of highly toxic gases and mixtures" (PDF). Asia Industrial Gases Association. 2011-07-16. AIGA 026/06. Archived from the original (PDF) on 2011-07-16. Retrieved 2021-09-22.
↑ "1988 OSHA PEL Project - Boron Tribromide | NIOSH | CDC". www.cdc.gov. 2020-02-25. Retrieved 2021-11-10.
↑ PubChem. "Boron trichloride". pubchem.ncbi.nlm.nih.gov. Retrieved 2021-11-10.
1 2 "Boron Tribromide". Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 17. 2014. doi:10.17226/18796. ISBN 978-0-309-30476-4.
↑ Methyl bromide - OECD HPVMETHYL BROMIDE CAS N°: 74-83-9
↑ Levin, B. C.; Paabo, M.; Gurman, J. L.; Harris, S. E.; Braun, E. (1987-12-01). "Toxicological interactions between carbon monoxide and carbon dioxide". Toxicology. 47 (1–2): 135–164. Bibcode:1987Toxgy..47..135L. doi:10.1016/0300-483x(87)90165-x. ISSN 0300-483X. PMID 3120355.
↑ Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 6 (PDF). Environmental Protection Agency. 2007. ISBN 978-0-309-11214-7.
↑ "Phosphorus(V) fluoride Safety Data Sheet". ThermoFisher Scientific . January 6, 2023.
↑ "Silicon Tetrachloride Hazardous Substance Fact Sheet" (PDF). New Jersey Department of Health . October 2010.
↑ "Stibine Hazardous Substance Fact Sheet" (PDF). New Jersey Department of Health and Senior Services . August 2001.
1 2 "Sulfur Tetrafluoride Safety Data Sheet" (PDF). Airgas .
↑ "Tungsten Hexafluoride Safety Data Sheet" (PDF). Airgas .

External links

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[decomposes-11] 1 2 Decomposes in gaseous form.

[12] Explodes in gaseous form.

[1] "California Fire Code California Code of Regulations,Title 24, Part 9, Chapter 2 - Definitions" (PDF).

[upenn-2] 1 2 "Environmental Health and Radiation Safety Department at the University of Pennsylvania".

[3] "Chemical Name Search". webbook.nist.gov. Retrieved 2021-11-10.

[:0-4] 1 2 "CDC - NIOSH Pocket Guide to Chemical Hazards - Arsenic (inorganic compounds, as As)". www.cdc.gov. Retrieved 2021-11-10.

[AIGA-5] 1 2 "Principles for the safe handling and distribution of highly toxic gases and mixtures" (PDF). Asia Industrial Gases Association. 2011-07-16. AIGA 026/06. Archived from the original (PDF) on 2011-07-16. Retrieved 2021-09-22.

[6] "1988 OSHA PEL Project - Boron Tribromide | NIOSH | CDC". www.cdc.gov. 2020-02-25. Retrieved 2021-11-10.

[7] PubChem. "Boron trichloride". pubchem.ncbi.nlm.nih.gov. Retrieved 2021-11-10.

[:1-8] 1 2 "Boron Tribromide". Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 17. 2014. doi:10.17226/18796. ISBN 978-0-309-30476-4.

[9] Methyl bromide - OECD HPVMETHYL BROMIDE CAS N°: 74-83-9

[10] Levin, B. C.; Paabo, M.; Gurman, J. L.; Harris, S. E.; Braun, E. (1987-12-01). "Toxicological interactions between carbon monoxide and carbon dioxide". Toxicology. 47 (1–2): 135–164. Bibcode:1987Toxgy..47..135L. doi:10.1016/0300-483x(87)90165-x. ISSN 0300-483X. PMID 3120355.

[13] Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 6 (PDF). Environmental Protection Agency. 2007. ISBN 978-0-309-11214-7.

[14] "Phosphorus(V) fluoride Safety Data Sheet". ThermoFisher Scientific . January 6, 2023.

[15] "Silicon Tetrachloride Hazardous Substance Fact Sheet" (PDF). New Jersey Department of Health . October 2010.

[16] "Stibine Hazardous Substance Fact Sheet" (PDF). New Jersey Department of Health and Senior Services . August 2001.

[:2-17] 1 2 "Sulfur Tetrafluoride Safety Data Sheet" (PDF). Airgas .

[18] "Tungsten Hexafluoride Safety Data Sheet" (PDF). Airgas .

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