Document KRmZYRovEzY0Dgqm0kkn0mXmr

Feature Article PLAINTIFFS;# ' '-,;rG-48af Exposure to Asbestos from Asbestos Gaskets Robert T. Cheng and Henry J. McDermott Chevron Corporation. P.O. Box 7924, San Francisco, California 94120 For more than 50 years, asbestos gaskets have been used in piping, valves, pumps, and other equipment to prevent leakage of fluids between solid surfaces. Although exposure data are available for workers in the gasket manufacturing industry, there are no published reports on asbestos exposures for gasket users. This article presents data on asbestos exposures during use and handling of asbestos gaskets in the oil and chemical industries. Users' time-weighted average exposures to asbestos during re placement of after-service gaskets, on-site fabrication (cutting) of sheet gaskets, and handling of new and after-service gaskets inside Gasket Trailers were all within the Occupational Safety and Health Administration (OSHA) Permissible Exposure limit. he practice of dry removal of after-service sheet gaskets, fol lowed by dry polishing of the seating surfaces with a power sander. could create a short-term asbestos exposure level in excess of the OSHA Excursion Limit. This type of potential, short-term, high exposure, however, can be eliminated simpiy by wetting the gaskets and seating surfaces prior to gasket replacement. In July 1989. the U.S. Environmental Protection Agency (EPA) prohibited the manufacture, importation, processing, and dis tribution in commerce of most asbestos gaskets by 1994. EPA's decision to ban asbestos gaskets was based solely on exposure data obtained from the gasket manufacturers. However, asbestos gaskets will continue to be used for many years in the workplace as in-service gaskets are removed and existing supplies are in stalled. Data from this investigation suggest that asbestos gaskets can be safely handled if proper procedures are followed. Cheng, R.T.; McDermott HJ.: Exposure to Asbestos from AsDestos Gaskets. Appl. Occup. Environ. Hyg. 6:588-591; 1991. Introduction .Asbestos gaskets are used extensivelv in piping (flanges), vaives. pumps, and other equipment to prevent leakage of fluids bertveen soiia surfaces. Ics high physical strength, heat and chemical resistance, and reasonable cost make asbestos a good choice where these features are important. In July 1989. the U.S. Environmental Protection Agency EPA) issued a hnai rule banning, in sages, the manufacare. importation, processing, and distribution in com merce of essenually all asbestos products. ' ' EPA placed asbestos gaskets under a Sage 2 ban. The effective dates for the Sage 2 ban are August 25. 1993. tor manufacture, importation, and processing and August 25. 1994. for dis tribution in commerce. EPA's decision to ban asbestos gas kets was based soieiy on exposure daa 'dt the asbestos gasket manufacturing facilities. A search of the literature showed no published studies reporting gasket users' as bestos exposures. Despite the EPA's recent action, asbestos gaskets will continue to be handled for many years in the workplace as in-service gaskets are replaced and inven tories of the remaining asbestos gasket material are used. This article presents daa on asbestos exposures during use and handling of 3sbestos gaskets in tne oil and chem ical industries. Some pumps contain asbestos in the pack ing material used to seal rouung shafts: these are not included in this study. - Types of Asbestos Gaskets The following three types of gaskets are commonly used in the oil and chemical process plants: Sheet gaskets, winch are typically Vit or 14 inch thick compressed asbestos sheets (containing ai least ~0% chrysotile asbestos) with Nitrile or Neoprene binder. Spiral wound gaskets, which consist of asbestos filler material compressed between Type 304 Stainless Steel spiral windings. The windings are held in place be tween an outside carbon steel compression centering ring and a Type 304 Stainless Steel inner ring. Spiral wound gaskets cost much more chan sheet gaskets but provide greater seaiabiliry and better blow-out prevenuon. Meol-iacketed gaskets, which consist of compressed asbestos filler material held within or between meai jackeung. Metal-jacketed gaskets are primarily used in large heat exchangers or vessel manways. Because the asbestos filler material in a meal-jacketed gasket is virtually enclosed by the meal jacket, asbestos exposure is not a problem for users of metal-iacketed gas kets. Therefore, the emphasis of this arucle is on spirai wouna gasKets and sheet gaskets. 588 I;wT-:ox-9i.i!6C7.'8eiiai : issi a;* OZZ'JP. ZNV1P.0N. fire. Sf?l TABL l. Womens' Asaesrcs exposures Ounng Sheet Gasxet Faoncancn Desemotion of Gasket Fabrication Tedimaues Samoie Duration 'mini Concentration (iServcci Long-Tom ssmoies Cooing wnn oower toear one rammer ounce 330 Cozing wnn oower near ana wreei tuner -03 rrr Curing win knife on a leao sunace taoie -90 rro Coning wnn oower near ana rammer ounce 2~ Curing win power srear ana scissors 170 : :oi Curing win power srear ana rammer ounce 353 * Curing wim wneei cuner ana rammer ounce $5 Shon-Term samples Curing wnn a sacer saw Curing wnn a saoer saw Curing wnn power snear and wneei cutter Curing wnn oower srear ana wneei cutter 55 129 55 r33 30 :a9 30 1.24 Spiral Wound Gaskets Spiral wound gaskets come prefabricated from the man ufacturers. Therefore, there ore no asbestos exposures re lated to the on-site gasket fabrication or alteration. During gasket replacement, an after-service spiral wound gasket can be easily lifted from the seating surfaces. In fact, for a vertically installed spiral wound gasket, the old gasket would fall off by its own weight os soon as the seating surfaces are separated if the gasket was not held in place (.Figure 1.). Before installing the new gaskets, workers may wipe the seaung surfaces clean with a rag or may remove any cor--'S'on with a wire brush. Consequently, asbestos fibers .aining on the seating surfaces are disturbed, resuiting m a brief exposure to airborne asoestos. Two snort-duration air samples were collected during replacement of rt%-o typ ical spiral wound gaskets in a piping system. The moni toring period covered the lining one disposal of the oia gaskets, wire brushing the surfaces of the flanges, and installing the new gaskets. Resuits snow nondetecmble air borne hber levels . detection limit = 0.06 hber. ee;. ind enting no worker exposure prooiem curing the use and handling of spirai wound gaskets. Fabrication of Sheet Gaskets At oil refineries and larger chemical plants, asbestos sheet gasket materials are usually purchased in bulk sneets. These are later fabricated (cut > into gaskets of various sizes and shapes at the faciiicv s machine shop. Various rypes of equipment and tools, including power shears, hammer punch, wheel cutter, knife, and saber saw. may be used in the fabrication process (Figure21 Workers asbestos ex posures during fabrication of sheet gasxets are summa rized in Table I. fever, full-shirt, personal air samples col lected during the davs of sheet gasket fabrication snowed that time-weighted average <TWA) exposure concentra tions ranged from 0.001 to 0.01" fiber.'cc. well within the 0.2 fiber.'cc Permissible Exposure Limit iPEL) set by the Occupational Safety and Heoitn Administration (OSHA).,:' -?l svwffc.v iys. nr, -utr '391 539 TABLE II. Workers' Short-Term Astiestos Exposures Ounng fleoiacsmem of Atter- Service Sheet Gaskets ___________________________________________________ Memod of Removal and Seating Surface Cleaning Sample Duration (mini Concentration (fibers/cci Diy removal: 2 valve gaskets. scncing/cnaning Dry removal: i oumo gasxet soaoing-cmsnng Dry removal: 2 flange gasxeis. saaomg'Drusning Dry removal: 2 pipe liange gaskets, rower sanoer Wet removal: 1 pumo gasket scraotng/cmsnmg Wei removal: 2 aioe liange gasxeis. prusning '9 0.:t 0.19 5 0.23 25 20 < 0.C6 !5 < O.Co Four short-term air sampies colleaed during the peak ac tion period of gasket fabrication showed that short-duration exposures ranged from 0.33 -to 0.-*9 fiber/cc. which were within the 1.0 fiber/cc OSHA Excursion Limit.'2' Although respirator.' protection is not required at these exposure levels by the OSHA .Asbestos Standard, workers are in structed to wear a naif-mask HEPA respirator as a precau tionary measure during fabrication of sheet gaskets. Replacing Sheet Gaskets The job of replacing sheet gaskets is generally a shortduration task, lasting from several minutes for replacing a small pipe flange gasket in the field to slightly under one hour for replacing a large-sized pump gasket in the shop. The sheet gaskets are under tremendous seating stress (e.g., 10.000 psi) during service, and they may be in contact with oxidizing or corrosive fluids. As the sealing surfaces are separated, sometimes the after-service sheet gasket tears, and pieces of the broken gasket material stick ugndy to one or both of the seating surfaces. A flat screw driver, putty knife, or scraper is used to lift the broken gasket off the metal, foilow-ed by scraping, brushing, polishing, or even sanding to clean the seaung surnces before installing the new gasket (Figure 3). When this cleaning is done in dry conditions, asbestos fibers can become airborne to create a potential inhalation hazard. To guard against ex- ceeding the OSHA PEL or Excursion Limit, or simply as a precautionary measure, workers should be required to wear a half-face HEPA respirator during dry removal of after-service sheet gaskets. Workers' short-term asbestos exposures were moni tored at four different refineries and chemical plants dur ing removal of after-semce sheet gaskets. Table II sum marizes the monitoring results under two methods of gasket removal and seating surface cleaning, i.e,, the old method of dry removal and dry surface cleaning and a new method of wet removal and wet surface cleaning. Short-term ex posures during the old wav of dry removal varied between 0.11 and 0.33 fiber/cc when surface cleaning was done with a scraper andor with a wire brush. One 3ir sample, colleaed during dry polishing of pipe flanges with a power sander. showed 1.4 fibers/cc for a task that lasted for 25 minutes. Although that particular air sample was colleaed in 1986 and was in compliance with the then applicable OSHA PEL of 0.2 fiber/cc (8-hour TWA), it would no longer meet the current 1.0 fiber/cc OSHA Excursion Limit A wet-work method was later established for the removal of after-service sheet gaskets. Typically, the wet-work pro cedure calls for the spraying of a solvent-based wetting agent (e.g., Chesterton ~23 Sprasolvo Penetrating Oil) to wet the gasket and the seating surfaces before removing and cleaning (Figure 4). Monitoring results indicate that, when the wet method is employed, workers' short-term asbestos exposures were all below detection (detection limit = 0.06 fiber/cc). Because very little time and labor are involved, and a spray can of wetting agent is all the material that is required the wet-work method for gasket replacement is well received by workers and by plant management. RGUHE 3. Srasnmg me gasket seanng surfaces. Gasket Trailer Worker Exposure At some of the larger petroleum refineries and chemical plants, gaskets of all types are kept in a special storage facility called the Gasket Trailer. The mailer is staffed bv an attendant whose duues are to maintain an inventory of gaskets, to coilea and dispose of used gaskets, and :o distribute new gaskets to other workers. During unit shut down and turnaround time, die attendant can be very busv as gaskets in many pieces of equipment are replaced. Six personal air sampies were colleaed from Gasket Trailer attendants during two maior shutdowns at an oil refiner*-' 590 :::ip -much hyg. -m practice oi ury remo^-n --a.-ua. lowed by dry polishing of the seating surfaces with a power sander. could create a short-term exposure in excess of the OSHA Excursion Limit. This potential exposure, how ever. can be controlled by wetting the gasket and tne seat ing surfaces prior to gasket replacement. FIGURE 4. Spraying a wetting agent Results show the trailer attendants' 8-hour TWA exposures ranged from.0.037 to 0.058 fiber/cc. well within the OSHA PEL . Conclusions Exposures to asbestos during on-site fabrication, han dling, and replacement of gaskets can be maintained well beiow the OSHA PEL with good work practices. The past Recommendations Asbestos gasketing matenals play an important role where their special features are needed. Their use remains ac ceptable as long as they are still commercially available. Replacing after-service sheet gaskets and cleaning the seat ing surfaces under wet conditions minimizes fiber release. In addition, regardless of the exposure level, a half-free HEPA respirator should be provided as a precautionary measure when the seating surface cleaning involves brush ing, polishing, or sanding, or when handling friable asbestoscontaining waste gasket matenals. References 1. ILS. Environmental Protection Agency: 40 CFR Part 763. .Asbestos: Man ufacture. Importation, Processing, and Distribution m Commerce Pro hibitions: Final Ruie. Fed. Reg. VoL 34. No. 132 (July 12.1989). 1 U.S. Department of Labor. Occupational Safety and Health Adminis tration: 29 CFR Pan 1926.58: Asoestos. Tremolite. Antnophylue. and Actinolite. Fed. Reg. VoL 51. No. 119 (June 20. 1988): amended in Fed. Reg. VoL 53. No. 178 (September 14.1988). - Received 6/28/SO: review aeasion mi'90: revision 9/10/90: secerned 10/10/90 ;ov: V; 7* 7 1P9L CCZ'JP ENVIRON. HYG. zi7) . _uly '991 591