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SECTION 1. CHEMICAL IDENTIFICATION

CHEMINFO Record Number: 149
CCOHS Chemical Name: Sulfur hexafluoride

Synonyms:
Sulfur fluoride
Sulphur fluoride
Sulphur hexafluoride
Sulfur fluoride (SF6)

Chemical Name French: Hexafluorure de soufre
Chemical Name Spanish: Hexafluoruro de azufre
CAS Registry Number: 2551-62-4
UN/NA Number(s): 1080
RTECS Number(s): WS4900000
Chemical Family: Sulfur and compounds / inorganic sulfur compound / fluoride / hexafluoride
Molecular Formula: F6-S
Structural Formula: S-F4

SECTION 2. DESCRIPTION

Appearance and Odour:
Colourless, odourless gas.(6,8,14)

Odour Threshold:
Odourless gas

Warning Properties:
NONE - Odourless, colourless gas.

Composition/Purity:
Sulfur hexafluoride is available commercially in various grades with a minimum purity of 99.8 mole%.(6) It is made to rigid specifications and the only permissible impurities are traces of air, carbon tetrafluoride at 0.05 weight% maximum and water (9 ppm weight maximum).(8) It is shipped as a liquefied compressed gas in steel cylinders or large containers under its own vapour pressure of 2210 kPa at 21.1 deg C.(14)

Uses and Occurrences:
Sulfur hexafluoride is used mainly in electrical and electronic equipment such as high-voltage circuit breakers and compact switching stations; as an insulating material in high-voltage coaxial lines, nuclear particle accelerators, X-ray equipment, microwave and radar equipment, cables, capacitors and transformers; and as a gaseous dielectric. It is also used as a tracer gas for studying air flow patterns, underground pipe leak detection and dispersion of air pollutants; in the operation of a chemical laser; as a source of fluorine atoms; in the plasma etching of semiconductor surfaces; as a protective atmosphere for casting of magnesium; for removing hydrogen and other gases from aluminum melts; for thermoacoustic insulation of double-pane windows; for increasing the water repellency and wet strength of Kraft paper; as a source of power from the reaction with lithium to produce heat and pressurizing recreation ball packages such as tennis balls to give improved shelf life. It also has some limited usage in a variety of unique applications ranging from medical applications to space research.(6,8,15)


SECTION 3. HAZARDS IDENTIFICATION

EMERGENCY OVERVIEW:
Colourless, odourless gas. Will not burn. COMPRESSED GAS. Can decompose at very high temperatures or when subjected to an electric discharge forming highly toxic decomposition products, including sulfur tetrafluoride and hydrogen fluoride. Simple asphyxiant. Can displace oxygen in air. Confined space hazard. Rapid evaporation of compressed gas may cause frostbite.



POTENTIAL HEALTH EFFECTS

Effects of Short-Term (Acute) Exposure

Inhalation:
Pure sulfur hexafluoride is an asphyxiant when present in high concentrations. Asphyxiants displace oxygen in the air and can cause symptoms of oxygen deprivation (asphyxiation) and suffocation. If sulfur hexafluoride is subjected to electrical discharge it can form highly toxic decomposition products.
The available oxygen should be a minimum of 18% or harmful effects will result. Effects of oxygen deficiency are: 12-16% - breathing and pulse rate are increased, with slight muscular incoordination; 10-14% - emotional upsets, abnormal fatigue from exertion, disturbed respiration; 6-10% - nausea and vomiting, inability to move freely, collapse, possible lack of consciousness; below 6% - convulsive movements, gasping, possible respiratory collapse and death. Since exercise increases the body's need for oxygen, symptoms will occur more quickly during exertion in an oxygen-deficient environment.(2,3) Survivors of oxygen deprivation may show damage to some or all organs including the central nervous system and the brain. These effects may or may not be reversible with time, depending on the degree and duration of the low oxygen and the amount of tissue injury.(3)
If sulfur hexafluoride is subjected to electrical discharge, highly toxic decomposition products are formed which may include sulfur tetrafluoride and other sulfur fluorides, sulfuryl fluoride, thionyl fluorides, sulfur oxides, hydrogen sulfide and/or hydrogen fluoride.(6,7,8) Exposure to these toxic decomposition products cause severe lung injury and pulmonary edema, a potentially fatal accumulation of fluid in the lungs. Symptoms of pulmonary edema include shortness of breath, pain in the chest and difficulty breathing. Symptoms may not develop for up to 24 hours after exposure.
One of two men knocked down in a confined space which contained sulfur hexafluoride and its electric arc decomposition products developed pulmonary edema. Airborne concentrations measured after the men had been rescued were 1500 ppm sulfur hexafluoride and 50 ppm sulfuryl fluoride.(9) In another report, irritation of the eyes and respiratory tract, with chest tightness, shortness of breath, headache, fatigue, nose bleeds, and vomiting, was experienced by 5 employees exposed to an unknown concentration of sulfur hexafluoride and its decomposition products for 6 hours over a 12 hour period. Employees noticed a "burning battery"-like odour and sulfur tetrafluoride was identified in air samples. Four workers continued to experience symptoms (most commonly intermittent nosebleeds) for 1 week to 1 month after the incident. One person showed temporary changes in lung function.(10)

Skin Contact:
Sulfur hexafluoride gas does not cause harmful skin effects. Direct contact with liquefied gas escaping from a high pressure cylinder may cause frostbite. Symptoms of mild frostbite include numbness, prickling and itching in the affected area. Symptoms of more severe frostbite include a burning sensation and stiffness of the affected area. The skin may become waxy white or yellow. Blistering and tissue death may also develop in severe cases.

Eye Contact:
Sulfur hexafluoride gas is not expected to cause harmful effects on the eyes. There is one report of temporary harmful effects following exposure to a very high airborne concentration (400000 ppm) for an unspecified duration.(11) Direct contact with liquefied sulfur hexafluoride gas escaping from a high pressure cylinder may freeze of the eye. Permanent eye damage or blindness could result.

Ingestion:
Ingestion is not an applicable route of exposure for gases

Effects of Long-Term (Chronic) Exposure

No human or animal information was located. Pure sulfur hexafluoride is considered an inert gas and is not expected to cause health effects following long-term exposure.

Carcinogenicity:

No human or animal information was located.

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 human or animal information was located.

Reproductive Toxicity:
No human or animal information was located.

Mutagenicity:
No human or animal information was located. Negative results were obtained in one unconfirmed test using cultured mammalian cells.

Toxicologically Synergistic Materials:
No information was located.

Potential for Accumulation:
Sulfur hexafluoride is not expected to accumulate in the body.


SECTION 4. FIRST AID MEASURES

Inhalation:
If the victim is unconscious or does not respond, 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 is difficult, trained personnel should administer emergency oxygen. If breathing has stopped, trained personnel should begin artificial respiration (AR) or, if the heart has stopped, cardiopulmonary resuscitation (CPR) or automated external defibrillation (AED) immediately. Quickly transport victim to an emergency care facility.

Skin Contact:
GAS: No health effects expected. LIQUEFIED GAS: Quickly remove victim from source of contamination and briefly flush with lukewarm, gently flowing water until the chemical is removed. DO NOT attempt to rewarm the affected area on site. DO NOT rub area or apply dry heat. Gently remove clothing or jewelry that may restrict circulation. Carefully cut around clothing that sticks to the skin and remove the rest of the garment. Loosely cover the affected area with a sterile dressing. DO NOT allow victim to drink alcohol or smoke. Quickly transport victim to an emergency care facility.

Eye Contact:
GAS: No effects expected. LIQUEFIED GAS: Quickly remove victim from source of contamination. Immediately and briefly flush with lukewarm, gently flowing water. If a contact lens is present, DO NOT delay irrigation or attempt to remove the lens until flushing is done. Cover both eyes with a sterile dressing. DO NOT allow victim to drink alcohol or smoke. Quickly transport victim to an emergency care facility.

Ingestion:
Ingestion is not an applicable route of exposure for gases.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).
Consult a doctor or Poison Control Centre for all exposures except minor instances of inhalation or skin contact.
Some first aid procedures recommended above require advanced first aid training. Protocols for undertaking advanced procedures must be developed in consultation with a doctor and routinely reviewed.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its conditions of use in the workplace.



SECTION 5. FIRE FIGHTING MEASURES

Flash Point:
Non-flammable gas

Lower Flammable (Explosive) Limit (LFL/LEL):
Not applicable

Upper Flammable (Explosive) Limit (UFL/UEL):
Not applicable

Autoignition (Ignition) Temperature:
Not applicable

Sensitivity to Mechanical Impact:
Stable gas. Not sensitive.

Sensitivity to Static Charge:
Sulfur hexafluoride has a very high dielectric constant and is a very good electrical insulating agent.(8,15) It is a non-flammable gas and is not sensitive to a static discharge.

Electrical Conductivity:
Not available

Minimum Ignition Energy:
Not applicable

Combustion and Thermal Decomposition Products:
Sulfuryl fluoride, thionyl fluorides, sulfur tetrafluoride and other sulfur fluorides (sulfur pentafluoride and disulfur decafluoride), sulfur oxides, hydrogen sulfide and hydrogen fluoride.(4,7,8)

Fire Hazard Summary:
Sulfur hexafluoride is not combustible and does not support combustion. However, it decomposes at very high temperatures (1000 deg C) and some of the decomposition products may be combustible. Cylinders may rupture or explode in the heat of a fire. Sulfur hexafluoride can displace air to the point where there is not enough oxygen to breathe.

Extinguishing Media:
Sulfur hexafluoride does not burn. Use extinguishing media appropriate for surrounding fire.

Fire Fighting Instructions:
Although sulfur hexafluoride does not burn, its thermal decomposition products may be combustible. Evacuate area and fight fire from a safe distance or a protected location. Approach fire from upwind to avoid toxic decomposition products.
If a fire occurs in an area where sulfur hexafluoride cylinders are used or stored, move cylinder or container from fire area if it can be done without risk. Use extreme caution since heat may rupture containers, which may rocket. Otherwise, fire-exposed containers 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. No part of a cylinder should be subjected to a temperature higher than 52 deg C (approximately 125 deg F). Most cylinders or containers are provided with a pressure relief valve designed to vent contents when they are exposed to elevated temperatures. Stay away from ends of tanks, but be aware that flying material from ruptured tanks may travel in any direction. Personnel should withdraw immediately in case of rising sounds from venting safety device or any discolouration of tanks due to fire.

Protection of Fire Fighters:
Sulfur hexafluoride is an asphyxiant and some of its decomposition products are toxic. Firefighters may enter the area if positive pressure self-contained breathing apparatus (NIOSH approved or equivalent) and full Bunker Gear is worn.



NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) HAZARD IDENTIFICATION

NFPA - Comments:
NFPA has no listing for this chemical in Codes 49 or 325.


SECTION 9. PHYSICAL AND CHEMICAL PROPERTIES

Molecular Weight: 146.05

Conversion Factor:
1 ppm = 5.96 mg/m3; 1 mg/m3 = 0.168 ppm at 25 deg C (calculated)

Physical State: Gas
Melting Point: -50.8 deg C (-59.4 deg F) at 224 kPa (14)*
Boiling Point: SUBLIMATION POINT: -63.7 deg C (-82.7 deg F) at 101.3 kPa (6,14)*
Relative Density (Specific Gravity): Not applicable (gas)
Solubility in Water: Practically insoluble (0.1-0.54 mL/100 mL water at 25 deg C).(6,14)
Solubility in Other Liquids: Soluble in ethanol and diethyl ether.(19)
Coefficient of Oil/Water Distribution (Partition Coefficient): Not available
pH Value: Not applicable
Viscosity-Dynamic: Not applicable
Vapour Density: 5.11 at 20 deg C and 101.3 kPa (air = 1) (6,14)
Vapour Pressure: Liquefied gas: 2156 kPa absolute (21.28 atm) at 21.1 deg C (6); 2308 kPa (22.77 atm) at 21.1 deg C (14); 3200 kPa (31.58 atm) at 37.8 deg C (14)
Vapour Pressure at 50 deg C: 4200 kPa (41 atm) (estimated from graph) (14)
Saturation Vapour Concentration: Not applicable; gas at normal temperatures.
Evaporation Rate: Not applicable; gas at normal temperatures. Liquefied gas will rapidly return to the gaseous state.
Henry's Law Constant: 4.58 x 10(+5) Pa.m3/mol (cited as 4.52 atm.m3/mol) (experimental) (13)
Critical Temperature: 45.55 deg C (114.0 deg F) (6,8)
Critical Pressure: 3759 kPa (37.1 atm) (8,14)

Other Physical Properties:
TRIPLE POINT: -50.52 deg C (-58.94 deg F or 222.63 deg K) at 225.31 kPa (8)
DIELECTRIC CONSTANT: 1.002 at 25 deg C and 101.3 kPa (8,14)
*NOTE: At atmospheric pressure, sulfur hexafluoride sublimes directly from solid to gas phase and does not have a stable liquid phase unless under a pressure of more than 221 kPa absolute (32 psia).(6)


SECTION 10. STABILITY AND REACTIVITY

Stability:
Stable at normal temperatures. It slowly decomposes at very high temperatures (1000 deg C), in the presence of an electric arc or when subjected to an electric discharge.(6,8,15)

Hazardous Polymerization:
Does not occur.

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.


With few exceptions, sulfur hexafluoride is chemically inert at normal temperatures and pressure and is completely stable in the presence of most materials to temperatures of about 204 deg C.(6,8)
DISILANE - explodes violently on contact.(16)

Hazardous Decomposition Products:
None

Conditions to Avoid:
Exposure to elevated temperatures, continuous electrical discharge, electric arcs, welding and cutting torches.

Corrosivity to Metals:
Sulfur hexafluoride is non-corrosive to all metals at normal temperatures.(6)

Corrosivity to Non-Metals:
Sulfur hexafluoride attacks elastomers, like styrene butadiene (SBR), polyacrylate, isoprene, natural rubber, and Viton (FKM).(21) Sulfur hexafluoride does not attack plastics, like Teflon and other fluorocarbons, like ethylene tetrafluoroethylene (Tefzel), polyvinyl chloride (PVC), nylon, polyurethane (riged), and high-density polyethylene; and elastomers, like ethylene-propylene, chloroprene, neoprene, polyurethane, butyl rubber (isobutylene isoprene), silicone and low-density polyethylene.(6,20,21)

Stability and Reactivity Comments:
Sulfur hexafluoride decomposes very slightly in the presence of silicon and carbon steels, mild steel and copper above 200 deg C and in quartz at 500 deg C. Decomposition does not occur with aluminum and silver at elevated temperatures.(6,8)


SECTION 11. TOXICOLOGICAL INFORMATION

No standard animal toxicity values were located.

Effects of Short-Term (Acute) Exposure:

Inhalation:
No effects were observed in 6 rats exposed to 17% sulfur hexafluoride for 18 hours or in 3 rats exposed to 80% for 2 hours. Exposure of about 50 rats to 80% sulfur hexafluoride and 20% oxygen for 16-24 hours was also without any effect.(17) Similarly, no effects were observed in 17 rats exposed to sulfur hexafluoride with 28% oxygen or in 8 rats exposed to sulfur hexafluoride with 22% oxygen for 6 hours. Autopsy conducted in 6 rats from the first group at 77 days following exposure and in 5 rats from the second group 135 days following exposure showed no harmful effects.(12) In another study, which is not available in English, effects on the central nervous system (CNS) and behaviour were observed in rats exposed to a very high airborne concentration (300000 mg/m3 or 50000 ppm) for a short (unspecified) period of time.(13, unconfirmed) There are insufficient details available to evaluate this study.

Mutagenicity:
No in vivo studies were located. Negative results are reported for one unconfirmed study using cultured mammalian cells.
Negative results (gene mutation) were obtained in cultured mammalian cells, with and without metabolic activation.(18, unconfirmed)


SECTION 16. OTHER INFORMATION

Selected Bibliography:
(1) Compressed Gas Association. Safety considerations for compressed gases and cryogenic liquids. In: Handbook of compressed gases. 4th ed. Kluwer Academic Publishers, 1999. p. 29-30
(2) Leikauf, G.D., et al. Inorganic compounds of carbon, nitrogen and oxygen. In: Patty's Industrial Hygiene and Toxicology. Edited by G.D. Clayton, et al. 5th ed. John Wiley & Sons, 2001
(3) Wilkenfeld, M. Simple asphyxiants. In: Environmental and Occupational Medicine. 3rd ed. Edited by W.N. Rom. Lippincott-Raven Publishers, 1998. p. 651-655
(4) Teitelbaum, D.T. Sulfur fluorides. In: Patty's industrial hygiene and toxicology. 5th ed. Vol. 3. Edited by E. Bingham et al. John Wiley and Sons, 2001. p. 752-757, 816-825
(5) American Conference of Governmental Industrial Hygienists (ACGIH). Sulfur hexafluoride. In: Documentation of the threshold limit values and biological exposure indices. 7th ed. ACGIH, 2001
(6) Compressed Gas Association. Sulfur hexafluoride. In: Handbook of compressed gases. 4th ed. Kluwer Academic Publishers, 1999. p. 607-610
(7) Morrison, H.D., et al. Decomposition of SF6 and production of S2F10 in power arcs. Government Reports Announcements & Index. Issue 03 (1996)
(8) Evans, F.E., et al. Fluorine compounds, inorganic, sulfur: sulfur hexafluoride. In: Kirk-Othmer encyclopedia of chemical technology. John Wiley and Sons, 2005. Available at: <www.mrw.interscience.wiley.com/kirk/kirk_search_fs.html> {Subscription required}
(9) Pilling, K.J. et al. Inhalation of degraded sulphur hexafluoride resulting in pulmonary oedema. Journal of the Society of Occupational Medicine. Vol. 38, no. 3 (1988). p. 82-84
(10) Kraut, A., et al. Pulmonary effects of acute exposure to degradation products of sulphur hexafluoride during electrical cable repair work. British Journal of Industrial Medicine. Vol. 47, no. 12 (Dec. 1990). p. 829-832
(11) Grant, W.M. et al. Toxicology of the eye. 4th ed. Charles C Thomas, 1993. p. 1350-1351
(12) Specht, H., et al. Inhalation of sulfur hexafluoride. Science. Vol. 14 (Dec. 21, 1951). p. 662-663
(13) US National Library of Medicine. Sulfur hexafluoride. Last revision date: 2002-11-08. In: Hazardous Substances Data Bank (HSDB). CHEMpendium. [CD-ROM]. Canadian Centre for Occupational Health and Safety (CCOHS). Also available at: <ccinfoweb.ccohs.ca/chempendium/search.html> {Subscription required}
(14) Yaws, C.L. Sulfur hexafluoride. In: Matheson gas data book. 7th ed. McGraw-Hill, 2001. p. 761-765
(15) Devilliers, D. et al. Fluorine compounds, inorganic: other inorganic fluorine compounds: sulfur hexafluoride. In: Ullmann's encyclopedia of industrial chemistry. 7th ed. John Wiley and Sons, 2005. Available at: <www.mrw.interscience.wiley.com/ueic/ueic_search_fs.html> {Subscription required}
(16) Fire protection guide to hazardous materials. 13th ed. Edited by A.B. Spencer, et al. National Fire Protection Association, 2002. NFPA 491
(17) Lester, D., et al. The toxicity of sulfur hexafluoride. Archives of Industrial Hygiene and Occupational Medicine. Vol. 2 (1950). p. 348-349
(18) Sulphur hexafluoride. IUCLID dataset. European Commission, European Chemicals Bureau, Feb. 2000. Available at: <ecb.jrc.it/IUCLID-Data-Sheet/2551624.pdf
(19) Sulfur hexafluoride. Hawley's condensed chemical dictionary. [CD-ROM]. 14th ed. Edited by R.J. Lewis, Sr. John Wiley and Sons, Inc., 2002
(20) Pruett, K.M. Chemical resistance guide for plastics: a guide to chemical resistance of engineering thermoplastics, fluoroplastics, fibers and thermoset resins. Compass Publications, 2000. p. 530-541
(21) Pruett, K.M. Chemical resistance guide for elastomers II: a guide to chemical resistance of rubber and elastomeric compounds. Compass Publications, 1994. p. C-350 to C-355
(22) National Institute for Occupational Safety and Health (NIOSH). Sulfur hexafluoride. In: NIOSH Manual of Analytical Methods (NMAM(R)). 4th ed. Edited by M.E. Cassinelli, et al. DHHS (NIOSH) Publication 94-113. Aug. 1994. Available at: <www.cdc.gov/niosh/nmam/nmammenu.html>

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: 2006-02-10

Revision Indicators:
Relative density 2006-09-28



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