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This document, prepared for the U.S. Environmental Protection Agency (U.S. EPA) by ICF Consulting, provides an overview of the formation and concentrations of byproducts produced when SF6 is exposed to various types of electric discharges. The document also discusses the health and safety concerns associated with these byproducts, including their irritating effects and toxicity. intended to serve as a resource for the SF6 Emission Reduction Partnership for Electric Power Systems.
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U.S. Environmental Protection Agency Office of Air and Radiation Global Programs Division 1200 Pennsylvania Avenue, NW Washington, DC 20460
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ICF Consulting 9300 Lee Highway Fairfax, VA 22031
January 2002
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This document provides summary information on sulfur hexafluoride (SF 6 ) byproducts. It was prepared for the U.S. Environmental Protection Agency (U.S. EPA), Global Programs Division by ICF Consulting, Inc., under Contract No. 68-W5-0068, Work Assignment No. 0005AA-83. This document was developed as a service to partners of the SF 6 Emissions Reduction Partnership for Electric Power Systems. The information presented in this document does not replace existing regulations or guidance regarding these compounds. Rather, this document was designed solely as an overview of the most significant byproducts identified to date. If you have suggestions and/or information that would improve this document, please send them to
Jerome Blackman / Program Manager U.S. Environmental Protection Agency MC 6205-J 1200 Pennsylvania Ave, NW Washington, DC 20460
or send an electronic mail to Blackman.Jerome@epa.gov. For more information on the SF 6 Emissions Reduction Partnership for Electric Power Systems , see http://www.epa.gov/highgwp1/sf6/index.html.
January 20 02 – Pa ge ii
1. Introduction and Background
Sulfur hexafluoride (SF 6 ) is a relatively nontoxic gas used in a number of applications for its inert qualities. The dielectric and other physical and chemical properties related to its lack of reactivity have led to the extensive use of SF 6 as an insulating medium in switching equipment (e.g., circuit breakers) by electric utilities. While SF 6 is inert during normal use, when electrical discharges occur within SF 6 -filled equipment, toxic byproducts can be produced that pose a threat to health of workers who come into contact with them. This paper discusses these byproducts and how they are formed, and also summarizes relevant health and safety concerns, as well as handling, detection, and safety procedures and guidelines.
U.S. EPA produced this background paper as a service to its partners in the SF 6 Emission Reduction Partnership for Electric Power Systems. This is a voluntary program in which partner companies agree to reduce SF 6 emissions through technically and economically feasible actions. SF 6 is a potent and persistent greenhouse gas, with a global warming potential approximately 24,000 times greater than carbon dioxide over a 100-year time horizon and a residency in the atmosphere of more than 3,000 years. Although SF 6 is critical to the reliable distribution of electricity, program participants recognize the importance of careful management and responsible use.
2. Formation and Concentrations of SF 6 Byproducts
Formation of SF 6 Byproducts
SF 6 can decompose into byproducts when exposed to four types of electric discharges (CIGRE^1 1997):
Each discharge can result in different mixtures and concentrations of byproducts.
Concentrations of SF 6 Byproducts
Numerous studies have characterized the byproducts of SF 6. Dervos and Vassiliou (2000) have summarized the most important ones (considering toxicity and risk) and the amounts of each formed under conditions similar to those found in gas insulated switchgear (GIS) equipment (see Table 1). These data were obtained by exposing SF 6 to repeated sparking under experimental conditions, and thus the decomposition products and concentrations formed under actual conditions can vary depending on the equipment used and the type of electrical discharge (CIGRE 1997).
(^1) CIGRE (the International Council on Large Electric Systems) is a permanent non-governmental and non
profit-making international association based in France. This group has established a working group (Study Committee 23) that is focused on concerns related to substations, including SF 6 and its bypro ducts. The web site established by Study Committee 23 is located at http://www.cigre-b3.org/.
Table 1. Gaseous SF 6 Decomposition Byproducts and Typical Concentrations During Repeated Sparking
Chemical Formula
Chemical Name Chemical Abstracts Service Registry Number
Experimental Concentration (percent by volume)a HF Hydrogen fluoride 7664-39-3 1. SOF 2 (SF 4 ) b^ Thionyl sulfide (sulfur tetrafluoride)
SOF 4 Sulfur tetrafluoride oxide 13709-54-1 0. SiF 4 Silicon tetrafluoride 7783-61-1 0. S 2 F 10 (SF 5 ) c^ Disulfur decafluoride 5714-22-7 0. SO 2 F 2 Sulfuryl fluoride 2699-79-8 0. SO 2 Sulfur dioxide 7446-09-5 0.
Table a dapted fro m Dervo s and Va ssiliou (200 0). a (^) Note that these concentrations represent the measured concentration for the experimental conditions studied. The
conditions were designed to simulate a real sparking occurrence; however, actual air concentrations in the vicinity of GIS will vary from these data. b (^) SF 4 is readily hydrolyzed to SOF 2. c (^) S 2 F 10 is referred to by some authors as sulfur pentafluoride or SF 5.
Additional byproducts that may be formed through arcing or other electrical discharges include SF 2 , SOF 10 , S 2 O 2 F 10 , and H 2 S, as well as a number of metal fluorides (e.g., copper fluoride (CuF 2 ), aluminum fluoride (AlF 3 )) and tungsten compounds (e.g., WF 6 , WO 3 ) (CIGRE 1997; U.S. EPA 2001a).
3. Health and Safety Concerns
Information on SF 6 byproducts has improved substantially in recent years. In its 1991 report, CIGRE identified only three gaseous SF 6 byproducts that pose a significant health threat (taking into account reaction quantities and toxicity): SOF 2 , SO 2 , and HF (Mauthe and Pettersson 1991). More recent research has identified S 2 F 10 as the byproduct of greatest concern due to its relatively high toxicity (James et al. 1993; Dervos and Vassiliou 2000), and occupational safety organizations have examined occupational exposures for several additional gaseous SF 6 byproducts.
Human Health Effects
According to information listed in the Hazardous Substances Databank (HSDB), gaseous SF 6 byproducts such as SF 4 , SiF 4 , SO 2 F 2 , SO 2 , and HF are extremely irritating to the eyes, nose, and throat (NLM 2001). Other human health effects of these gases include pulmonary edema, skin and eye burns, nasal congestion, and bronchitis due to their corrosive characteristics. Solid byproducts such as AlF 3 and CuF 2 dusts are also irritating to exposed skin and eyes, and the nose, throat, and lungs when inhaled (NLM 2001). If copper salts are inhaled in sufficient concentration so that it reaches the gastrointestinal tract (via cough and mucociliary mechanisms), they act as irritants producing salivation, nausea, vomiting, gastric pain, hemorrhagic gastritis, and diarrhea (NLM 2001).
5. Handling, Detection, and Safety Procedures and Guidelines
Numerous guidelines have been published regarding the handling, detection, and safety of SF 6 gas and its byproducts. These guidelines basically specify that employees minimize exposure to SF 6 byproducts by wearing protective equipment when handling and disposing SF 6 byproducts and by meeting specific exposure concentration standards.
Handling Procedures and Guidelines
SF 6 recycling and handling guidelines are described in detail in CIGRE guide number 117 (CIGRE 1997). Procedures specific to individual manufacturers’ equipment types are also reported to be available directly from manufacturers. SF 6 handling procedures as provided by utility partners can be found on U.S. EPA’s SF 6 Emissions Reduction Partnership for Electric Power Systems web page http://www.epa.gov/highgwp1/sf6/ (U.S. EPA 2001a). These guidelines often include procedures for handling hazardous SF 6 byproducts. U.S. EPA has also prepared a catalog that lists guidelines and standards for the handling and management of SF 6 (U.S. EPA 2001b).
Detection Procedures and Guidelines
SF 6 byproducts are difficult to detect chemically under normal working conditions. The presence of various SF 6 electrical discharge decomposition products and impurities (as well as the presence of SF 6 itself) makes measurement of the different byproducts problematic. A recent report in Transmission and Distribution World summarized methods that may allow for on-site and field monitoring of SF 6 byproducts with portable instrumentation (Baumbach et al. 2000). The NIOSH Pocket Guide to Chemical Hazards (NIOSH 1997) presents measurement methods and signs and symptoms of exposure for S 2 F 10 , SF 4 , SO 2 , HF, and SO 2 F 2 , as well as SF 6.
SF 6 byproducts such as SOF 3 and SF 4 have a strong irritating “rotten egg” odor at low concentrations, and, at high concentrations, are irritating to the eyes, nose, throat, and lungs (U.S. EPA 2001; NLM 2001). Solid byproducts (i.e., metal fluoride byproducts) are white, gray, or tan powders that often can be observed when present and are irritating to exposed skin (Edison Technical Center 1997; U.S. EPA 2001a; NLM 2001). However, these gross physical indicators of the presence of byproducts should not be relied upon as safety mechanisms due to the possibility of severe injury, especially given that the most toxic byproduct, S 2 F 10 , is generally odorless in pure form at typical environmental temperature.
Safety Procedures and Guidelines
Safety precautions for hazardous SF 6 byproducts are often addressed in SF 6 handling procedures for gas-insulated electrical equipment. (See the electric utility partners’ SF 6 handling procedures on U.S. EPA’s web page http://www.epa.gov/highgwp1/sf6/ (^) (U.S. EPA 2001a). Also see the U.S. EPA catalog – available from the same web page – of SF 6 guidelines and standards (U.S. EPA 2001b).) Many SF 6 handling procedures require the worker to wear protective clothing and an approved respirator when the presence of decomposition products are suspected (e.g., when the SF 6 -filled breakers are exposed to a severe arc for an abnormal period of time due to improper operation of the breaker). Industrial hygiene practices can be found in the NIOSH Pocket Guide to Chemical Hazards (NIOSH 1997), including respirator selections, exposure limits, signs and symptoms of exposure, and procedures for emergency treatment for S 2 F 10 , SF 4 , SO 2 , HF, SO 2 F 2 , fluorides, as well as SF 6.
Table 2 compiles the available occupational safety standards for the gaseous byproducts identified in Table 1 of this paper. SF 6 is included for reference. Table 3 lists exposure limits for fluorides, aluminum, and copper compound dusts. The parameters presented in Tables 2 and 3 are defined below.
C Permissible exposure limit - ceiling (PEL-ceiling): Defined by the Occupational Safety and Health Administration (OSHA), the PEL-ceiling is a specified concentration of the chemical in air that must not be exceeded during any part of the working exposure for any amount of time.
C Recommended exposure limit - ceiling (REL-ceiling): The REL - ceiling is concentration of the chemical in air that should not be exceeded, as recommended by the National Institute for Occupational Safety and Health (NIOSH).
C Recommended exposure limit - time-weighted average (REL-TWA): The REL-TWA is the time-weighted average concentration for up to a 10-hour workday during a 40-hour workweek that should not be exceeded, as recommended by NIOSH.
C Permissible exposure limit - time-weighted average (PEL-TWA): Defined by OSHA, the PEL-TWA is the time-weighted average concentration that must not be exceeded during any 8-hour work shift of a 40-hour work-week.
C Short-term exposure limit (STEL): Defined by OSHA, the STEL is the concentration that must not be exceeded over a 15-minute period.
C Recommended short-term exposure limit (RSTEL): The RSTEL is a 15-minute time- weighted average concentration that should not be exceeded at any time during a workday, as recommended by NIOSH.
C Level immediately dangerous to life or health (IDLH): Developed by NIOSH, the IDLH is the maximum concentration from which, in the event of respirator failure, one could escape within 30 minutes without irreversible health effects (designed to aid in the selection of a respirator only).
C Threshold limit value - ceiling (TLV-C): Established by the American Conference of Governmental Industrial Hygienists (ACGIH), the TLV-C is a specified concentration of the chemical in air that should not be exceeded during any part of the working exposure for any amount of time.
C Threshold limit value - time-weighted average (TLV-TWA): Established by ACGIH, the TLV-TWA is a the time-weighted average concentration that should not be exceeded based on a normal 8 hour work day/40 hour work week.
Occupational exposure limits were not located for some of the SF 6 byproducts (including SOF 4 and SiF 4 ). The occupational standards listed in Tables 2 and 3 were developed by occupational health organizations in the United States. CIGRE literature and information in HSDB indicate that international exposure values also exist for some SF 6 byproducts (Mauthe and Pettersson 1991; NLM 2001).
Table 3. Available Inhalation Exposure Limits for Solid Byproducts of SF 6
Substance Parameter Exposure limit value Defining organization Fluorides (measured as fluorine (F))
PEL-TWA 2.5 mg/m 3 OSHA T L V- TW A 2.5 mg/m 3 ACGIH Aluminum soluble salts (measured as aluminum (Al))
P E L- TW A a^ 2 mg/m 3 OSHA REL-TWA 2 mg/m 3 NIOSH Copper dusts (e.g., CuF 2 ) PEL-TWA 1 mg/m 3 OSHA R E L- TW A 1 mg/m 3 NIOSH IDLH 100 mg /m 3 NIOSH T L V- TW A 1 mg/m 3 ACGIH
All values listed in this table were cited in NLM (2001) and NIOSH (1997) a (^) PEL was vacated by the U.S. Circuit Court of Appeals on June 30, 1993; however, OSH A may enforce it under the
“general duty clause” in Section 5(a)(1) of the Occupational Safety and Health Act. Some states enforce vacated PELs.
The Department of Transportation (DOT) provides guidance for emergency response for transportation incidents involving hazardous materials in its 2000 Emergency Response Guidebook. Health warnings, fire mitigation, evacuation procedures, protective clothing prescriptions, and first aid procedures are available for SO 2 F 2 (DOT no. 2191) in Guide 123 and SF 4 (DOT no. 2418) and HF (DOT no. 1052) in Guide 125 (DOT 2000).
5. References
American Conference of Government Industrial Hygienists (ACGIH). 1989. Threshold Limit Values and Biological Exposure Indices for 1989-1990. Cincinnati, Ohio.
Baumbach, J.I., Pilzecker, P., Trindade, E., and J. Meinders. 2000. Diagnosing the health of SF 6 switchgear. Transmission and Distribution World Vol. 52 (1), Jan 1, 2000, 3 pp.
International Council on Large Electric Systems (CIGRE). 1997. SF 6 Recycling Guide. Publication number 117; Task Force 23.10.01. August 1997.
Department of Transportation (DOT). 2000. 2000 Emergency Response Guidebook. A Guidebook for First Responders During the Initial Phase of a Dangerous Materials Incident. Internet site at http://hazmat.dot.gov/gydebook.htm.
Dervos, C.T., and P. Vassiliou. 2000. Sulfur hexafluoride (SF 6 ): Global environmental effects and toxic byproduct formation. J. Air and Waste Manage. Assoc. 50:137-141.
Edison Technical Center. 1997. Insulating Materials for Distribution Switchgear in Today’s Environment. Internet site located at http://169.207.59.145/Library/TheLine/pdf/97-04/04-97-etc 01.html. Site dated April 1997; accessed September 2000.
Greenberg, L.A., and D. Lester. 1950. The toxicity of sulfur pentafluoride. Arch. Indust. Hygiene and Occupat. Med. 2:350-353. [cited in James et al. 1993]
James, D.R., I. Sauers, G.D. Griffin, R.J Van Brunt, J.K. Olthoff, K.L. Stricklett, F.Y. Chu, J.R. Robins, and H.D. Morrison. 1993. Investigation of S 2 F 10 production and mitigation in compressed SF 6 -insulated power systems. IEEE Electrical Insulation Magazine 9(3):29-51.
Kraut, A. and R. Lilis. 1990. Pulmonary effects of acute exposure to degradation products of sulphur hexafluoride during electrical cable repair work. British Journal of Industrial Medicine 47:829-832.
Mauthe,G., and K. Pettersson. 1991. Handling of SF 6 and its decomposition products in gas insulated switchgear (GIS). Electra , no. 136:69-89 (Part 1) and no 137:81-105 (Part 2). June 1991. (Publication of Working Group 23, International Council on Large Electric Systems (CIGRE)).
National Institute for Occupational Safety and Health (NIOSH). 1997. NIOSH Pocket Guide to Chemical Hazards. U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, Washington, D.C. NIOSH Publication no. 97-140; NTIS no. PB-
National Library of Medicine (NLM). 2001. Hazardous Substances Databank (HSDB). Internet site located at http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB.
Occupational Safety and Health Administration (OSHA). 2000. Chemical Sampling Information. January 19. http://www.osha-slc.gov/dts/chemicalsampling/toc/toc_chemsamp.html
Renshaw, B., and M. Gates. 1946. “Di-sulfur decafluoride,” in Chemical Warfare Agents and Related Chemical Problems Parts I-II , Office of Scientific Research and Development, National Defense Research Committee, Washington, D.C. NTIS no. PB-158508, Chapter 4, pp. 24-29. [cited in James et al. 1993]
Sauers, I., G.D. Griffen, D.R. James, R.J. Van Brunt, J.K. Olthoff, K.L. Stricklett, H.D. Morrison, M. Frechette, et al. 1995. Investigation of S 2 F 10 production and mitigation in compressed SF 6 -insulated power systems. Final report. Volume 1: Executive Summary. Prepared under Cooperative Research and Development Agreement No. ORNL 90-0002. October 1995. ORNL/M-4314.
Sauers, I. 1998. Plasma Chem. Plasma Process. 8: 247-262. [cited in Sauers et al. 1995]
U.S. Environmental Protection Agency (U.S. EPA). 2001a. SF 6 Emissions Reduction Partnership for Electric Power Systems: SF 6 Handling Procedures. Internet web site at http://www.epa.gov/highgwp1/sf6/partner_resources/index.html..
U.S. Environmental Protection Agency (U.S. EPA). 2001b. Catalog of Guidelines and Standards for the Handling and Management of Sulfur Hexafluoride (SF 6 ). Prepared for the U.S. EPA, Office of Air and Radiation, Global Programs Division. Prepared by ICF Consulting, Fairfax, VA, under Contract No. 68 W5-0068. July. http://www.epa.gov/highwp1/sf6/pdf/sf6utility7.pdf..
Van Brunt, R.J., and J.T. Herron. 1990. IEEE Trans. Electr. Insul. E1-25: 75-94. [cited in Sauers et al. 1995]
