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CHEMINFO Record Number: 49
CCOHS Chemical Name: Acetylene, dissolved


Chemical Name French: Acétylène
Chemical Name Spanish: Acetileno
CAS Registry Number: 74-86-2
UN/NA Number(s): 1001
RTECS Number(s): AO9600000
Chemical Family: Unsaturated aliphatic hydrocarbon / alkyne
Molecular Formula: C2-H2
Structural Formula: H-C#C-H (# denotes a triple bond)


Appearance and Odour:
Pure acetylene is a colourless, odourless gas. Technical and commercial grades have a garlic odour due to the presence of impurities.(5)

Odour Threshold:
240 mg/m3 (226 ppm) (detection) (4); 657 mg/m3 (620 ppm) (not specified) (8) 1300-2750 mg/m3 (1222-2585 ppm) (not specified) (4)

Warning Properties:
NOT RELIABLE - odour threshold about the same magnitude as the NIOSH recommended exposure limit.

Crude acetylene and some commercial grades contain traces of ammonia, arsine, hydrogen sulfide, and phosphine. A number of case reports of injury or death following acetylene exposure have been attributed to the presence of toxic impurities such as phosphine.(1) (See the CHEMINFO Review on phosphine for more information.) Acetylene is normally shipped in cylinders under pressure as a solution in acetone with a porous filler. (See the CHEMINFO Review on acetone for more information.)

Uses and Occurrences:
Primarily used as a raw material in the production of chemicals such as acetaldehyde, acetic acid, acrylonitrile, perchloroethylene, vinyl chloride, and trichloroethylene. Also used for oxyacetylene welding, cutting and heat-treating. Small amounts used for lighting purposes in buoys and beacons, and as a fuel in atomic absorption instruments.


Colourless gas with no or slight garlic-like odour depending on purity. FLAMMABLE GAS. Can be ignited by static discharge or sparks. May decompose with explosive violence at elevated temperatures and pressures. COMPRESSED GAS. Forms very sensitive explosive metallic salts. Simple asphyxiant. May reduce oxygen available for breathing. High concentrations may accumulate in confined spaces.


Effects of Short-Term (Acute) Exposure

Acetylene is essentially non-toxic at concentrations below the lower explosive limit (LEL) of 2.5% (25000 ppm).(1,3) At higher concentrations, it has anesthetic action and at even higher levels is a simple asphyxiant. Its narcotic action is about 1.5 times that of ethylene.(3)
The main health concern of acetylene is that it can displace oxygen in the atmosphere and cause suffocation due to lack of oxygen (asphyxiation). In one case, a person working in a process generating acetylene became unconscious rapidly and died after he put his head inside a calcium carbide feed hopper where it is believed there was an oxygen deficiency and a high (up to 80%) acetylene concentration.(9)
For every 5% (50000 ppm) increase in acetylene in the atmosphere, there is about a 1% decrease in oxygen content. Normal atmospheric content of oxygen is 21.5%. Oxygen content in the atmosphere must not fall below 18% or effects of oxygen deficiency will occur. It is unlikely that enough acetylene will escape and accumulate in an open workplace to significantly displace oxygen in the atmosphere. However, in a confined space, it is possible for high concentrations of acetylene to accumulate. In such an event, a significant amount of oxygen may be displaced.
Effects of oxygen deficiency are as follows: 12-16% oxygen content can cause the breathing and pulse rate to increase and muscular coordination can be slightly disturbed; 10-14% oxygen content can cause emotional upset, abnormal fatigue and disturbed respiration; 6-10% oxygen content can cause nausea, vomiting, collapse or loss of consciousness; oxygen content below 6% can cause convulsive movements, possible respiratory collapse and death.(11,12)
Acetylene produces varying degrees of temporary narcosis when administered with oxygen at concentrations of 100,000 ppm (10%) or greater. In an experiment, in which volunteers were exposed to high concentrations of acetylene in an atmosphere where oxygen content was artificially maintained, central nervous system (CNS) effects were observed.(6)
Phosphine and arsine, two very toxic gases, are sometimes present in acetylene at low concentrations. There are case reports of injury and death attributed to the impurities in acetylene.(9) For more information on phosphine, see CHEMINFO record 716E.

Skin Contact:
Gas is not irritating. Some sources report that the liquid could cause frostbite. However, this is not possible because acetylene cylinders contain acetylene gas dissolved in acetone. Any skin contact with liquid would be with acetone since the acetylene would be rapidly released. Acetone is a slight skin irritant.

Eye Contact:
Gas is not irritating. Some sources report that the liquid could cause frostbite. However, this is not possible because acetylene cylinders contain acetylene gas dissolved in acetone. Any eye contact with liquid would be with small amounts of acetone, since the acetylene would be rapidly released. Acetone is a moderate eye irritant.

Not applicable. Acetylene is a gas.

Effects of Long-Term (Chronic) Exposure

None reported


No information available

The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.

The American Conference of Governmental Industrial Hygienists (ACGIH) has not assigned a carcinogenicity designation to this chemical.

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
No information available

Reproductive Toxicity:
No information available

No information available

Toxicologically Synergistic Materials:
No information available

Potential for Accumulation:
Does not accumulate


This product is flammable. Take proper precautions (e.g. remove any sources of ignition). Also, take proper precautions to ensure your own safety before attempting rescue, (e.g. wear appropriate protective equipment, use the "buddy" system). Remove source of contamination or move victim to fresh air. If breathing has stopped, properly trained personnel should begin artificial respiration or cardiopulmonary resuscitation (CPR) immediately. Oxygen may be beneficial if administered by a person trained in its use, preferably on a doctor's advice. Obtain medical attention immediately.

Skin Contact:
Not applicable for gas. If skin contact occurs with liquid from cylinders of acetylene dissolved in acetone, immediately flush with lukewarm, gently flowing water for at least 5 minutes, or until the chemical is removed. Remove contaminated clothing, shoes and leather goods (e.g. watchbands, belts). If irritation persists, repeat flushing. Obtain medical advice immediately. Completely decontaminate clothing, shoes and leather goods before reuse or discard.

Eye Contact:
Not applicable for gas. If eye contact occurs with liquid from cylinders of acetylene dissolved in acetone, immediately flush the contaminated eye(s) with lukewarm, gently flowing water for 10 minutes, or until the chemical is removed, while holding the eyelids open. Obtain medical advice immediately.

Not applicable to gas.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest). Consult a doctor and/or the nearest Poison Control Centre for all exposures except minor instances of inhalation or skin contact.
Some recommendations in the above sections may be considered medical acts in some jurisdictions. These recommendations should be reviewed with a doctor and appropriate delegation obtained, as required. All first aid procedures should be periodically reviewed by a doctor familiar with the material and its condition of use in the workplace.


Flash Point:
Flammable gas. Can be ignited at all normal temperatures. A closed cup flash point of -18 deg C (0 deg F) has been reported.(10)

Lower Flammable (Explosive) Limit (LFL/LEL):
2.5% (7)

Upper Flammable (Explosive) Limit (UFL/UEL):
81% (2); 100% if there is a substantial energy ignition source, and under certain conditions of pressure, container size and shape.(5)

Autoignition (Ignition) Temperature:
305 deg C (581 deg F) (7); 406-440 deg C (763-824 deg F) (2)

Sensitivity to Mechanical Impact:
Information not available

Sensitivity to Static Charge:
Acetylene gas is extremely flammable and can be readily ignited by static discharge if concentration exceeds lower explosive limit. Minimum ignition energy: 0.019 millijoules.(14)

Fire Hazard Summary:
Flammable gas. Can readily form explosive mixtures with air over a very wide range. Low ignition energy. Explosion hazard in confined spaces. Pure acetylene can explode under certain conditions of elevated pressure and temperature and container size.(5) Reacts with active metals to form explosive acetylide compounds.

Extinguishing Media:
Dry chemical powder, carbon dioxide, foam, water spray or fog. Stop flow of gas.(7)

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or from a location protected from the effects of an explosion. Approach fire from upwind to avoid hazardous vapours and toxic decomposition products.
For fires involving flammable gases, the best procedure is to stop the flow of gas when escaping gas is burning. It may be dangerous to extinguish the flame and allow the gas to flow, as an explosive mixture may be formed with air and if ignited may cause far greater damage than if the fire had been allowed to burn. It may be desirable to extinguish the fire with carbon dioxide or dry chemical powder where necessary, to allow immediate access to valves to shut off the supply. If the leak cannot be stopped, and if there is no risk to the surrounding area, let the fire burn itself out.
If a leak has not ignited, use water spray in large quantities to disperse the gas and to protect personnel attempting to stop a leak.
Containers may rupture in the heat of the fire. Isolate materials not yet involved in the fire and protect personnel. Move containers from fire area if this can be done without risk. Otherwise, fire-exposed cylinders or tanks should be cooled by application of hose streams and this should begin as soon as possible (within the first several minutes) and should concentrate on any unwetted portions of the container. If this is not possible, use unmanned monitor nozzles and immediately evacuate the area. Caution must be used in approaching the fire and applying water.
For a massive fire in a large area, use unmanned hose holder or monitor nozzles; if this is not possible withdraw from fire area and allow fire to burn. Stay away from ends of tanks. Withdraw immediately in case of rising sound from venting safety device or any discolouration of tank due to fire.
Acetylene, itself, is only slightly hazardous to health. However, it can displace oxygen in the air, reducing the amount available for breathing. Firefighters may enter the area if positive pressure self-contained breathing apparatus (MSHA/NIOSH approved or equivalent) and full Bunker Gear is worn.


NFPA - Health: 0 - Exposure, under fire conditions, would be no more hazardous than an ordinary combustible material.
NFPA - Flammability: 4 - Will rapidly or completely vaporize at atmospheric pressure and normal ambient temperature, or readily disperse in air and burn readily.
NFPA - Instability: 3 - Capable of detonation or explosive decomposition or explosive reaction, but requires a strong initiating source or must be heated under confinement before initiation, or reacts explosively with water.


Molecular Weight: 26.04

Conversion Factor:
1 ppm = 1.065 mg/m3; 1 mg/m3 = 0.94 ppm at 25 deg C (calc.)

Physical State: Gas
Melting Point: -82.2 deg C (-116 deg F) at 69 kPa gage (10 psi gage) (5)
Boiling Point: -75 deg C (-103 deg F) at 170 kPa abs (24.7 psi abs) or 69 kPa gage (10 psi gage).(2,5)
Relative Density (Specific Gravity): Not applicable (gas)
Solubility in Water: 1.7 vol/vol at 0 deg C (32 deg F) and 1 atmosphere (101.kPa).(5)
Solubility in Other Liquids: Soluble in many organic solvents (e.g. acetone, benzene, ethanol); slightly soluble in carbon disulphide.
Coefficient of Oil/Water Distribution (Partition Coefficient): Not available
pH Value: Not applicable
Vapour Density: 0.908 (air = 1) (2,5)
Vapour Pressure: 4479 kPa (44.2 atm) at 21.1 deg C (2); 4378 kPa (43.2 atm) (5)
Vapour Pressure at 50 deg C: Greater than 7000 kPa (69 atm) (estimated from graph) (2b)
Saturation Vapour Concentration: Not applicable
Evaporation Rate: Not applicable
Critical Temperature: 36.0 deg C (97 deg F) (2,5)
Critical Pressure: 6250 kPa (61.7 atm) (5)

Other Physical Properties:
TRIPLE POINT: -82.2 deg C (-116 deg F) at 122 kPa abs.(5)
SUBLIMINATION POINT: -83.3 deg C (-118 deg F) at 101.33 kPa.(5)


Stable at standard temperature and pressure. Gaseous acetylene may decompose explosively to hydrogen and carbon at elevated temperatures and pressures. The higher the pressure, the easier it is for an explosion to occur. Pressures below 207 kPa abs. (30 psi abs.) or 103 kPa gage (15 psi gage) are regarded as safe.(5,7)

Hazardous Polymerization:
Can occur when heated or compressed

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.

BRASS - in the presence of wet acetylene and ammonia, brass with more than 60% copper can react readily to produce explosive acetylides.(7)
CALCIUM HYPOCHLORITE - can react to produce explosive chloroacetylenes.(10)
COPPER, MERCURY AND SILVER SALTS - produce acetylides from ammoniacal solutions. The dried acetylides are extremely sensitive and can explode violently.(7)
HALOGENS (e.g. bromine, chlorine, iodine, fluorine) - can react explosively.(7,10)
HEAVY METALS (e.g. copper, mercury, silver): react to produce explosive acetylides.(7,10)
HYDRIDES (e.g. sodium hydride, cesium hydride, rubidium hydride) - react vigorously if moisture is present.(7)
LIQUID NITROGEN - can react explosively.(10)
NITRIC ACID - contact with acetylene in the presence of mercury salts can produce explosive trinitromethane.(10)
OXYGEN - produces explosive mixtures (10)
OZONE - reacts explosively (10)
PERCHLORIC ACID - explosions have occurred in atomic absorption spectrometers using acetylene-nitrous oxide flames when sample solutions containing perchloric acid were used.(10)
POTASSIUM - molten potassium ignites, then explodes in acetylene.(10)

Hazardous Decomposition Products:

Conditions to Avoid:
Static discharge, sparks, open flames, heat and other sources of ignition.

Corrosivity to Metals:
Not corrosive


Effects of Short-Term (Acute) Exposure:

Animals have shown tolerance at 10 per cent acetylene. In studies with dogs, cats and rabbits, acetylene acts as an anesthetic (causes drowsiness and unconsciousness) at concentrations about 20 per cent (200,000 ppm). Recovery may occur if oxygen content of atmosphere is maintained. In an oxygen-deficient atmosphere (50 per cent acetylene) in air, death may occur after 5-10 minutes.(1,13) Rodents exposed to 25, 50 and 80 percent acetylene in oxygen for 1-2 hours daily up to 93 hours, showed no organ weight changes or cellular injuries. 80% acetylene/20% oxygen mixture caused a rise in blood pressure in the cat.(3)


Selected Bibliography:
(1) National Institute for Occupational Safety and Health. Criteria for a recommended standard. Occupational exposure to acetylene. Washington, DC : U.S. Department of Health, Education, and Welfare; Public Health Service; Center for Disease Control; National Institute for Occupational Safety and Health, 1976
(2a) Braker, W.; et al Acetylene. In: Matheson gas data book. 6th edition. Lyndhurst, NJ, 1980. p. 1-8
(2b) Yaws, C.L. Matheson gas data book. 7th ed. McGraw-Hill, 2001. p. 5
(3) Cavender, F. Aliphatic hydrocarbons. In: Patty's industrial hygiene and toxicology. 4th ed. Vol. II. Toxicology. Part B. Edited by G.D. Clayton et al. John Wiley and Sons, Inc., 1994. p. 1254-1255
(4) Verschueren K. Handbook of environmental data on organic chemicals. 3rd ed. Van Nostrand Reinhold Company, 1996. p. 122-123
(5) Compressed Gas Association. Handbook of compressed gases. 3rd ed. Van Nostrand Reinhold Company, 1990. p. 213-222
(6) Davidson, B.M. Studies of intoxication II : the action of acetylene. Journal of Pharmacology and Experimental Therapeutics. Vol. 25, no. 2 (1925). p. 119-135
(7) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 325; NFPA 49; NFPA 491
Ruth, J.A. Odor thresholds and irritation levels of several chemical substances : a review. American Industrial Hygiene Association. Vol. 47 (Mar. 1985). p. A-142 to A-143
(9) Jones, A.T. Fatal gassing in an acetylene manufacturing plant. Archives of Environmental Health. Vol. 1 (1960). p. 417-421
(10) Urben, P.G., ed. Breatherick's handbook of reactive chemical hazards. 5th ed. Vol. 1. Butterworth-Heinemann Ltd, 1995. p. 262-266, 1843
(11) Lipsett, M., et al. Inorganic compounds of carbon, nitrogen, and oxygen: oxygene, O2. In: Patty's industrial hygiene and toxicology. 3rd ed. Vol. II. Toxicology. Part F. Edited by G.D. Clayton et al. John Wiley and Sons, 1994. p. 4597-4600
(12) Wilkenfeld, M. Simple asphyxiants. In: Environmental and Occupational Medicine. Edited by W.N. Rom. 2nd edition. Little, Brown and Company, 1992. p. 535-538
(13) Acetylene. In: Documentation of the threshold limit values and biological exposure indices. 6th ed. American Conference of Governmental Industrial Hygieneists, 1991. p. 15-17
(14) Chemical safety sheets: working safety with hazardous chemicals. Kluwer Academic Publishers, 1991. p. 16
(15) European Economic Community. Commission Directive 93/72/EEC. September 1, 1993

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.

Review/Preparation Date: 1997-03-24

Revision Indicators:
US transport 1998-02-01
TDG 2002-05-27
Chemical name 2002-06-05
US transport 2002-12-04
Extinguishing media 2003-04-14
WHMIS disclosure list 2003-06-16
Bibliography 2006-01-18
Vapour pressure at 50 deg C 2006-01-18

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