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Journal of Toxicology and Environmental Health, Part B, 10:259–286, 2007Copyright © Taylor & Francis Group, LLCISSN: 1093-7404 print / 1521-6950 onlineDOI: 10.1080/15287390600974957
EXPOSURE TO AIRBORNE ASBESTOS DURING REMOVAL AND INSTALLATION OF GASKETS AND PACKINGS: A REVIEW OF PUBLISHED AND UNPUBLISHED STUDIES
Amy K. Madl, Katherine Clark, Dennis J. Paustenbach
ChemRisk, Inc., San Francisco, California, USA
In recent years, questions have been raised about the health risks to persons who have been occupationally exposedto asbestos-containing gaskets and packing materials used in pipes, valves, and machinery (pumps, autos, etc.). Upuntil the late 1970s, these materials were widely used throughout industrial and maritime operations, refineries,chemical plants, naval ships, and energy plants. Seven simulation studies and four work-site industrial hygiene stud-ies of industrial and maritime settings involving the collection of more than 300 air samples were evaluated to deter-mine the likely airborne fiber concentrations to which a worker may have been exposed while working withencapsulated asbestos-containing gaskets and packing materials. Each study was evaluated for the representative-ness of work practices, analytical methods, sample size, and potential for asbestos contamination (e.g., insulation onvalves or pipes used in the study). Specific activities evaluated included the removal and installation of gaskets andpackings, flange cleaning, and gasket formation. In all but one of the studies relating to the replacement of gasketsand packing using hand-held tools, the short-term average exposures were less than the current 30-min OSHAexcursion limit of 1 fiber per cubic centimeter (f/cc) and all of the long-term average exposures were less than thecurrent 8-h permissible exposure limit time-weighted average (PEL-TWA) of 0.1 f/cc. The weight of evidence indi-cates that the use of hand tools and hand-operated power tools to remove or install gaskets or packing as performedby pipefitters or other tradesmen in nearly all plausible situations would not have produced airborne concentrationsin excess of contemporaneous regulatory levels.
Gaskets and packing materials are used in every industry that makes use of pipes, pumps, andvalves. The introduction of the steam engine created the first market for commercial asbestos gas-kets (Kelleher & Bartlett, 1983). Several other commercial applications of asbestos soon followed,including insulation, friction products, and packing materials. Asbestos gaskets and packing materi-als became widely used in all types of industrial settings. Asbestos was favored because it was easilymanipulated, inexpensive, flame-retardant, compressible, heat-resistant, and an effective sealant(Kelleher & Bartlett, 1983).
Historically, gaskets and packing were made of encapsulated or bound asbestos materials. Theasbestos fibers in gaskets were primarily incorporated with rubber, styrene-butadiene rubber, orneoprene binders, while asbestos packing materials were saturated with rubber, neoprene, wax, oil,or Teflon. In most cases, chrysotile asbestos was the only asbestos fiber used in these materials,although crocidolite asbestos gaskets were sometimes used in acidic environments, such as thosefound in certain chemical manufacturing processes.
For most of the 20th century, the majority of gaskets and packing materials contained asbestos.It was not until the late 1970s and early 1980s that asbestos was phased out of gaskets and packingdue to questions raised about the health risks to persons occupationally exposed to these products.Until this time, asbestos-containing gaskets and packing materials were widely used throughoutindustrial and maritime operations, refineries, chemical plants, naval ships, and energy plants(Lindell, 1972; Cheng & McDermott, 1991; Millette et al., 1996; Spence & Rocchi, 1996). Navalspecifications required that asbestos-containing gaskets be used for a variety of applications on ships(U.S. Navy, 1924, 1953, 1985).
The authors appreciate the assistance of Carl Mangold for providing invaluable insight into the worker activities associated with theremoval and installation of gaskets and packing. Although we initiated this evaluation, financial support for the underlying research wasprovided by a pump manufacturer involved in asbestos-related litigation regarding gaskets and packing. One or two of the authors hasserved or may serve as an expert witness in related litigation.
Address correspondence to Amy K. Madl, ChemRisk, Inc., 25 Jessie Street at Ecker Square, Suite 1800, San Francisco, CA 94105,USA. E-mail: [email protected]
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Relatively few studies in the 1970s and 1980s evaluated exposures related to working with gas-kets and packing, especially when compared to the many evaluations of asbestos insulation, due toa perception that gasket/packing exposure were negligible or relatively small. The first comprehen-sive study that characterized potential worker exposures to airborne fibers during the removal andinstallation of asbestos-containing gaskets was that conducted by the U.S. Navy by Liukonen et al.(1978). This unpublished work was undertaken as part of an ongoing industrial hygiene assessmentof asbestos exposures to workers in naval settings. The Navy concluded that with simple house-keeping measures, airborne concentrations could be kept well below the contemporaneous per-missible exposure limits (PELs). The Navy’s use of asbestos gaskets and packing materials continuedinto the 1980s.
The extensive use of asbestos insulation on pipes and machinery up until the late 1960s andearly 1970s made it difficult for work-site studies to accurately assess the airborne fiber concentra-tion of asbestos to which a worker was exposed during the removal and replacement of asbestosgaskets and packing materials. That is, the background airborne concentration of asbestos on shipsdue to insulation often exceeded the contribution that might have been due to handling gasketsand packing. Later studies tried to limit background asbestos levels by simulating the work activity incontrolled environments (e.g., laboratory test facilities). It was not until 1991 that the first study ofthis type (involving gaskets) was published in the peer-reviewed literature (Cheng & McDermott,1991). In this work-site study, Cheng and McDermott (1991) found that asbestos gaskets could besafely handled if appropriate procedures were followed. Since then, a number of studies have eval-uated airborne fiber exposures during these activities, and some of these have raised concern aboutthe potential health hazards of these products.
Studies, both published and unpublished, that evaluated airborne fiber exposures due to han-dling gaskets and packing were generally conducted at a work site or simulated in a controlled envi-ronment. Some studies evaluated the peak (short-term, e.g., minutes) concentrations and others thedaily (4 to 8 h) airborne fiber concentrations. This review, to the best of our knowledge, is the firstto bring together all of the published studies (data), as well as selected unpublished studies, on air-borne fiber concentrations associated with the handling of asbestos-containing gaskets and packingmaterials. Seven simulation studies (or series of simulation studies) and four-work site studies of indus-trial and maritime settings, which involved the collection of more than 300 air samples, were analyzed.
The objective was to determine the likely airborne fiber concentrations generated by standardwork practices of handling encapsulated asbestos gaskets and packing materials. Each study wasevaluated for work practices, analytical methods, sample size, and potential for asbestos contamina-tion (e.g., insulation on valves or pipes used in the study). Based on the data from these studies,comparisons were made to determine whether certain factors influenced the magnitude of expo-sure to airborne asbestos. These factors included: (1) the type of material worked on (gaskets orpacking), (2) the types of tools used to manipulate the asbestos-containing materials, (3) whetherwork activities were simulated or performed at the work site, and (4) whether the work was per-formed wet or dry.
The data from these studies were used to develop a range of likely airborne concentrations fordifferent worker activities which then were compared to current and historical occupational expo-sure limits (e.g., OSHA PELs and American Conference of Governmental Industrial Hygienists[ACGIH] threshold limit values [TLVs]). Results of this analysis should provide the scientific and reg-ulatory community with a better understanding about the potential health hazards posed by work-ing with asbestos gaskets and packing materials.
HISTORY OF ASBESTOS GASKETS AND PACKING IN THE CONTEXT OF THE U.S. NAVY
During the 1970s, researchers and agencies noted that encapsulated asbestos products, includ-ing gaskets and packing, posed little health risk due to the belief that asbestos fibers were bound orencapsulated in a binding material (Selikoff, 1970; Lindell, 1972). In 1972, the InternationalAgency for Research on Cancer (IARC) proceedings described packing as a soft and resilient satu-rated asbestos material and indicated that asbestos posed no health risk in the use of asbestos-based
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gasket materials (Lindell, 1972). More recently, the final rule of the National Emission Standards forHazardous Air Pollutants (NESHAP) regulations, promulgated in 1990, categorized asbestos-contain-ing gaskets and packing as Category I nonfriable asbestos-containing material based on the beliefthat these products were unlikely to produce airborne concentrations of asbestos above regulatorylimits during normal use (NESHAP, 1990). The NESHAP regulations state that asbestos gaskets andpacking generally do not release significant amounts of asbestos fibers even when broken or dam-aged; however, the regulations also state that various forces and deterioration can cause nonfriable(e.g., gaskets) materials to release fibers and dust.
In contrast to gasket and packing materials, it was understood beginning in the 1960s thatasbestos insulation could pose a significant health hazard if airborne concentrations were not lim-ited. Several studies from the 1960s and 1970s documented high rates of asbestos-related diseasesamong insulation workers (Marr, 1964; Selikoff, 1970; Selikoff et al., 1979). Many of these studiesinvolved shipyard workers, as naval ships extensively used asbestos insulation on pipes and machinery.Shipyard workers were frequently exposed to high airborne concentrations of asbestos as insulationwas removed and replaced during the maintenance and overhaul of pipes and machinery.
Historically, asbestos insulation made up the overwhelming majority of the total weight ofasbestos used in industrial and shipyard settings. For example, on a World War II-era Navaldestroyer, which contained at least 48 tons of asbestos, gaskets and packing accounted for muchless than 1% of the total asbestos used onboard the vessel while insulating materials accounted forover 95% of the total asbestos used. The insulating materials contained amosite and chrysotileasbestos fibers not encapsulated in any binding material and were friable. In contrast, the gasketsand packing contained chrysotile asbestos fibers encapsulated with binding agents. Although theencapsulated nature of gaskets made them unlikely to release significant levels of asbestos fibers,degradation (due to operating conditions or physical manipulation) of the binding matrix would beexpected to increase the number of fibers released from the gasket during removal.
During the 1960s, the association between mesothelioma and asbestos became well estab-lished in the scientific and medical literature, and increasing concerns about the health hazards ofasbestos prompted the discontinuation of asbestos insulation. During the late 1960s and early1970s, the U.S. Navy introduced substitute materials for asbestos insulation, although asbestos wasstill used in smaller amounts (Beckett, 1976; Kurumatani et al., 1999). In the mid-1970s, the U.S.Navy and various other industries conducted preliminary studies to characterize asbestos exposuresassociated with other asbestos-containing materials, such as gaskets. However, these studies wereunpublished and entailed a relatively small sample size, characterized a limited range of tasks, andprovided limited detail on the workplace procedures used. Furthermore, in some of the field stud-ies, background fiber concentrations attributable to insulation were not characterized and couldhave potentially overwhelmed the contribution due to handling gaskets and packing. Subsequentstudies tried to address these shortcomings and limit the concentration of asbestos in backgroundair by conducting the work in a controlled environment.
BACKGROUND ON GASKET AND PACKING REPLACEMENT
Gaskets are used to prevent fluid leakage by forming a seal between two sides of a pipe joint ormachinery housing (Figure 1). In the past, the asbestos content of gaskets typically ranged from 40to 90%, with binders making up the rest of the material. Gasket replacement generally involvesthree different activities: gasket formation (if precut gaskets are not used), removal of old gasketsfrom the flange surface, and installation of a new gasket. Gaskets can either be cut from rolledsheets or bought preformed. Unless purchased precut, gaskets are either made in the field by theworker replacing the gasket or in a gasket fabrication shop. Several types of manual and poweredtools are used to form gaskets from asbestos sheets, including hand punches, machine punches,scribes, nibblers, circular cutters, machines shears, and pen knives.
Gaskets may be produced in bulk at workshops containing specialized tools for gasket forma-tion. Some of these tools, such as machine and hammer punches, remove the gasket out of thesheet, much like a hole punch, while other machines, such as saws and nibblers, shear the gasket
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material. These machines are generally used in a shop rather than the work site due to their size.Depending on the tool used, gasket formation normally takes between 1 and 10 min. Workshoptools, such as power shears, punches, saws, and nibblers, generate higher airborne fiber exposuresduring the formation of gaskets than when handheld tools are used.
In the field, workers will generally use smaller hand-held tools to cut the gasket to fit a particularflange. Scribes are often used to make an outline of the gasket on the sheet before it is cut. Some ofthe hand tools that are used to form a gasket include ballpeen hammers, knives, and shears. Gasketformation does not take very long in the field, although operation of manual tools for this processgenerally requires more time than workshop tools.
The most time-consuming step in gasket installation is often the first step, which involves reposi-tioning the pipes so that the flange faces can be accessed. This may require setting up chainfalls andpulleys to support the pipes or to pull them apart. Once the flange faces are open, the gasket can beremoved. Workers performing gasket replacement must remove the old gasket material, whichmight be adhered to the flange face surface, before a new gasket can be installed. If the adheredgasket material is not removed entirely, the new gasket will not form an adequate seal. Hand scrap-ers and hand-held wire brushes are the most common tools used to remove adhered gasket mate-rial, although power wire brushes may also be used for gaskets that are particularly difficult toremove or if the flange face is rusted. The hand scraper is generally a sharp blade that, when held ata low angle and forced against the face of the flange, peels off the old gasket (Figure 2). The wirebrush has sharp wires that are effective in removing small pieces of gasket and rust. The time spentcleaning a flange during the removal of a gasket can range anywhere from a few minutes to 10 min-utes, depending on the size of the flange and how tightly the old gasket is adhered. The new gasketis placed on the flange face and the fitting is reassembled accordingly. The process of gasket instal-lation takes a variable amount of time, depending on the size and accessibility of the flanges.
Packing consists of rings cut from a slick fibrous rope, which are wrapped around the shafts ofvalves, compressors, and pumps to prevent the contents from leaking out at the shaft (Figure 3 and 4).The rings of packing are usually removed using a device that resembles a corkscrew (Figure 5). Dur-ing the installation process, new packing rings that are either precut or cut from a rope of packing areplaced around the shaft in such a way that the gaps in the rings are staggered around the shaft.
FIGURE 1. A new gasket against a pipe flange. The gasket forms a seal once the opposing flange and bolts are put in place, preventingthe contents of the pipe from leaking out.
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GENERAL DESCRIPTION OF THE STUDIES
The literature on gasket and packing operations includes both work-site and simulation studies.The simulation studies involve characterizing exposures associated with specific products or workertasks by reenacting work activities in a contaminant-free environment. These types of studies oftenprovide useful insight as to the extent a particular work activity might contribute to a worker’s over-all exposure and are preferred over collecting samples at work sites when other worksite sourcescould confound measurements (Madl & Paustenbach, 2002a, 2002b; Paustenbach et al., 2004).
At times, some researchers have chosen to use Tyndall lighting as an adjunct to their exposureassessment of gaskets and other asbestos-containing material (Longo et al. 2002). This techniquecan be useful as a teaching tool to encourage workers to wear respiratory protection because it canidentify particles smaller than that recognized by the naked eye. However, it is not informative withrespect to characterizing human health hazards, because Tyndall lighting is unable to differentiatebetween types of airborne particles (e.g., asbestos versus nuisance dust). Furthermore, Tyndall light-ing is not able to distinguish respirable (<10 mm in diameter) versus nonrespirable particles orthose particles which are responsible for disease (i.e., pneumoconiosis) or other related effects. Atbest, Tyndall lighting can aid in assessing the magnitude of an emitted dust from certain activities inconnection with evaluating the efficiency of exhaust hoods or engineering controls.
Both duration and magnitude of exposure are important in assessing occupational exposure toasbestos and for estimating 8-h time-weighted average (TWA) concentrations. Unfortunately, fewstudies on gaskets and packings report the average duration of an activity and/or the typical numberof activities a worker performed in a day. Due to different sampling times (i.e., full shift versus activ-ity only), the data presented in this collection of studies cannot always be directly compared. Somestudies, such as the Navy Bremerton study, report an activity average only. Other studies sampleover the course of an entire workday, but do not separately measure the activity average concentra-tion or report the number of times that a particular activity was conducted.
Several simulation studies evaluated a worker’s daily exposure by collecting breathing-zonesamples while the worker repeatedly performed specific tasks over the course of an 8-h workday.Not all of these studies reported the number of repetitions of the task; however, many of the studiesreported that the worker performed eight repetitions of the activity of interest over the course of theday (Spencer, 1998a, 1998b; Boelter et al., 2002; Mangold et al., 2006). In general, for an indus-trial or maritime setting, gasket and packing replacement is usually conducted on an intermittentbasis (Liukonen et al., 1978; Spence & Rocchi, 1996). In addition, workers removing and replacing
FIGURE 2. A gasket is scraped off the casing of a centrifugal pump using a scraper tool. Workers indicate that scraping is the most com-mon method of removing residual gasket material.
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gaskets and packing must spend time traveling to each work site, installing support systems for thepipes and machinery, removing bolts, and setting up tools. Because a typical pipefitter installs andfabricates pipes and performs many different activities, it would be typical for him to replace nomore than one or two gaskets a day. However, for the sake of conservatism, eight installations orremovals per day of a gasket or packing could be considered an upper bound estimate of whatwould have plausibly occurred in the daily life of a pipefitter or millwright. It is worth noting thatgasket work being performed in a workshop can be conducted at a higher rate than in the field.
This analysis of industrial hygiene data of gasket and packing removal and installation werelimited to industrial and maritime settings (e.g., refinery, chemical, and ship/shipyard). Studies ofgasket removal for passenger automobiles (e.g., engines and exhausts) have been recently publishedor performed (Boelter & Spencer, 2003; Liukonen & Weir, 2005; Paustenbach et al., 2006; Blakeet al., 2006). These studies were not included in the pooled exposure estimates of gasket replace-ment activities because gasket work of a maintenance worker or pipefitter at an industrial plantcould be considered substantially different from that of an automobile mechanic in a repair shop.
FIGURE 3. New rings of packing. Multiple rings of packing are wrapped around a valve stem or machine shaft to prevent fluid from leakingout around the shaft/valve stem. Packing is usually a braided rope-like material impregnated with a slick substance such as graphite or oil.
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For example, automobile gaskets are often available preformed, thus not requiring gasket formationat the work site, and the size of gasket and time and work required for access to an automobile gas-ket is usually much less than for gaskets for industrial applications (e.g., pumps, valves). However,with these differences in mind, qualitative comparisons were made between airborne fiber expo-sures for gasket work in industrial and automobile repair settings when specific work activities(i.e., cleaning of flange surface) appeared to be similar.
Eight published studies involving removal and installation of industrial or maritime gaskets andpacking materials were identified in the literature. All eight published studies were included in thisevaluation, as well as two unpublished studies or series of studies. The unpublished studiesincluded in this analysis are those of the Navy Regional Medical Center and John Spencer(Liukonen et al., 1978; Spencer, 1998a, 1998b). One additional published study of an automobilegasket processing workshop was included in the analysis (Yeung et al., 1999). The Navy Bremertonstudy was included because of its historical significance and those of Spencer were includedbecause their methodologies were similar and comparable in quality to many of the published
FIGURE 4. Rings of packing on the shaft of a centrifugal pump. The upper casing of this pump has been removed to show the location ofthe rings of packing along the pump shaft. The rings of packing prevent the pumped fluid from leaking out.
FIGURE 5. A worker using a hooked tool to remove packing from the shaft of a centrifugal pump.
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simulation studies on gaskets and packing. Although other unpublished studies exist involving thecollection of airborne fibers during gasket and packing activities, they were not included in thisevaluation because of small sample size, lack of information about sampling and analytical meth-ods, poor descriptions of work activities, or potential interference from asbestos and nonasbestosfiber contamination. The published and unpublished studies located and reviewed by the authorsare listed in Table 1 (see reference list for titles) (NRF Prototype Engineering, 1984; Rossnagel &Associates, 1984; McCrone Environmental, 1988; CONSAD Research Corporation, 1990;Liukonen, 1990–1991; Occupational and Environmental Health Consultants, 1991; RJ Lee Group,1992; Orr Safety Corporation, 1992–1994; Matteson, 1998; Spencer, 2001).
The authors are also aware of test results of gasket cutters collected by OSHA and described ina personal letter to the corporation of interest (Baty, 1980). In this testing, airborne fibers weremeasured during gasket cutting operations for four workers (n=8). No airborne fibers weredetected in air samples (n=2) collected for 15 min for two workers and a TWA of 0.11 fibers percubic centimeter (f/cc) and 0.2 f/cc were reported for samples collected over a full workday for theother two workers (n=6) performing gasket cutting operations (Baty, 1980). During the time ofsample collection, the OSHA PEL was 2 f/cc. Similar to the reasons that the already mentionedstudies were excluded, the 1980 data collected by OSHA were not included in the analysisdescribed herein because of a lack of information regarding (1) how gasket cutting was performed,(2) type of facility and other potential asbestos-containing gasket products manufactured at thesite, (3) potential operations adjacent to the gasket cutting that may interfere with asbestos analy-sis, (4) specific activities performed by the workers, and (5) methods used for sample collectionand analysis. In addition, the sample size was limited as airborne fibers were only detected for twoworkers.
Of the studies on gaskets and packing materials evaluated for this assessment, all reportedphase-contrast microscopy (PCM) data, while only a few conducted both PCM and transmissionelectron microscopy (TEM) analyses. Most studies that performed the TEM analysis applied theresults as a stand-alone method, when, for the purpose of evaluating occupational exposure, itshould be used in conjunction with the PCM NIOSH method 7400 as described in NIOSH method7402 for TEM analysis (NIOSH, 1994a, 1994b). This method of TEM analysis applies the fraction ofasbestos fibers of the total fiber count, as measured by TEM analysis, to the PCM data.
It is worth noting that the NIOSH methods 7400 and 7402 for airborne asbestos specify onlycounting those fibers that are greater than 5 μm in length and 0.25 μm in width and with at least a3:1 aspect ratio, in part because PCM does not have the power to visualize smaller fibers. TheOSHA PEL was based on counts of fibers that can be visualized by PCM analysis, and thereforeOSHA specifies PCM analysis (with or without the TEM analysis described in method 7402) for theevaluation of occupational exposures to airborne asbestos. While the NIOSH methods 7400 and7402 are still used today to determine workplace compliance to the OSHA PEL for asbestos, thesemethods are limited in their ability to characterize all respirable fibers. Both fiber size and type mustbe characterized to understand the hazard posed by fibers, with an emphasis on those which arethought to pose the greatest risk. In their draft risk assessment, the U.S. Environmental ProtectionAgency (EPA) concluded that respirable fibers (less than 0.4 μm in diameter) greater than 10 μmlength pose the greatest risk of asbestos-related disease (Berman & Crump, 2003). While not widelyused, the recent ISO Standard method allows one to characterize both fiber size and type, as wellas determine the fiber size distribution of airborne asbestos and differentiate free fibers from fibersassociated with a nonrespirable matrix (ISO, 1995). Data derived from the ISO method would beideal for applying workplace exposures to dose-response and risk assessment models. All studiesevaluated in this assessment utilized the NIOSH methods for comparisons to the OSHA PEL, which,as defined by OSHA, is a measurable and comparable value that cannot be exceeded withoutfurther action by the employer to reduce exposures (OSHA, 1994b).
For the purpose of comparing exposure data across different gasket and packing studies, as wellas for comparison to the OSHA PEL for asbestos, this analysis emphasized the PCM data fromworker breathing zone samples. However, when reported by the study authors, TEM data arereported alongside the PCM data. Since the TEM data were reported in different manners, (i.e.,
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TABLE 1. Published and Unpublished Studies Reviewed and Considered by Authors for Inclusion in This Analysis (See References forStudy Titles)
Author(s) Year Included? Reasons included or excluded from this analysis
Navy Bremerton Study 1978 yes Unpublished worksite study; first and most well-known study on gasket activities; samples analyzed by PCM (analytical protocol included in study)
Baty 1980 no Unpublished work-site sampling; small sample size; limited information regarding the work site, operations, worker tasks, and collection and analytical methods
Mangold 1982–1991 (published in 2006)
yes Series of published simulation studies; 8-h samples collected over several days; wide variety of work methods performed; characterized background levels of asbestos contamination; emulated Navy study; samples analyzed by PCM (NIOSH P&CAM 239 and NIOSH 7400) and, in some cases, TEM (NIOSH 7402)
NRF Prototype Engineering 1984 no Work-site unpublished study; high background; small sample sizeRossnagel & Associates 1984 no Unpublished simulation study; spiral wound gaskets only; small
sample sizeMcCrone
Environmental1988 no Unpublished worksite study; limited description of worker activities
CONSAD 1990 no Final unpublished report includes sampling data; basis for data not explained; no details on sampling method
Liukonen 1990–1991 no Unpublished work-site studies; limited description of sampling methods and worker activities
Cheng and McDermott 1991 yes Published work-site study; collected long-term and short-term samples during gasket removal and formation activities; samples analyzed by PCM
Occupational and Environmental Health Consultants/ORR Safety Corporation
1991–1994 no Unpublished work-site study; limited descriptions of worker activities
RJ Lee Group 1992 no Unpublished work-site study; samples collected during the disassembly of one pump; small sample size
McKinnery and Moore 1992 yes Published simulation study; short-term samples of valve packing removal and replacement; several samples collected; samples analyzed by PCM
Millette and Mount 1993 yes Published simulation study; collected short-term samples during packing removal; samples analyzed by PCM (NIOSH 7400) and TEM (NIOSH 7402)
Spence and Rocchi 1996 yes Published worksite study; collected samples during wet gasket removal; samples analyzed by PCM (NVN 2939) and TEM (NIOSH 7402)
Matteson, Georgia Institute of Technology
1998 no Unpublished simulation studies; PCM and/or direct TEM not always conducted; gaskets did not always contain asbestos; not representative of worker conditions; methods unclear
Spencer 1998 yes Two separate unpublished simulation studies: 8-h samples collected over 11 d; variety of work methods specific to gaskets and packing performed; samples analyzed by PCM (NIOSH 7400)
Yeung et al. 1999 yes Published Australian worksite study; collected samples during fabrication of automobile gaskets using powered tools; samples analyzed by PCM and TEM.
Fowler 2000 yes Published simulation study; collected samples during sawing of sheet gasket material; samples analyzed by PCM and TEM
Spencer 2001 no Unpublished simulation study; small sample size; gasket and packing activities not always clearly separated from other pump and compressor activities
Longo, Egeland, Hatfield, and Newton
2002 yes Published simulation study; collected several short term samples during variety of gasket removal activities; samples analyzed by PCM (NIOSH 7400) and TEM (modified EPA Level II—indirect)
Boelter, Crawford, and Podraza
2002 yes Published simulation study; collected several 8-h samples; gasket and packing activities studied; samples analyzed by PCM (OSHA ID-160)
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both fibers greater than 5 μm and fibers of all sizes), no comparisons between TEM data wereattempted. Several of the studies analyzed bulk samples for the asbestos content of the gasket andpacking materials that were removed from the valve or flange. Nearly every simulation study identi-fied in our assessment analyzed bulk samples of packing and gaskets and all of these studiesreported finding chrysotile, but not amphibole fibers.
In evaluating the data from these studies, it was often necessary to calculate means and stan-dard deviations from reported data. These calculations were performed using one-half the limit ofdetection for all samples that reported nondetectable quantities, unless otherwise noted. All calcu-lations performed by the authors are noted in the text and in the data tables.
EVALUATION OF WORKSITE AND SIMULATION STUDIES
U.S. Navy Study, Regional Medical Center, Bremerton, WAIn 1978, the U.S. Navy released the first large-scale study evaluating occupational exposures
during all types of asbestos gasket work (Liukonen et al., 1978). Due to the size, scope, and histori-cal significance of this study, a separate discussion of this study is warranted. The study was con-ducted by the Navy Regional Medical Center at Bremerton and reported by L. R. Liukonen andR. R. Beckett. Previous studies performed by the Navy had only studied a few workers or did notreport details of the study methods. The 1978 study was designed to produce enough data to drawconclusions regarding the potential exposures associated with gasket work, including the handlingand storage of gasket materials, the formation of gaskets from asbestos sheets, and the removal andinstallation of gaskets. The study also evaluated whether use of housekeeping procedures and/orlocal exhaust ventilation significantly reduced airborne fiber concentrations. Housekeeping wasdefined as the use of HEPA filter-equipped vacuum cleaners (Portovacs) to clean areas, placementof waste material in sealed containers, maintaining clean work areas that were free of debris accu-mulation, and storage of material in sealed, impermeable polyethylene bags. The study also evalu-ated exposures associated with specific tasks, including hand, mechanical, and machine gasketpunching, hand shaping, machine shearing and nibbling, gasket installation, hand scraping, andwire brushing. All of the samples were collected in the breathing zone of workers performing thegasket-related tasks. The data showed that the housekeeping measures significantly lowered air-borne fiber exposures, to levels less than the contemporaneous OSHA PEL for asbestos. Althoughthis study was not published in the peer-reviewed literature, it was the first study of its kind and isoften referred to during discussions of asbestos exposures associated with gasket work (Liukonenet al., 1978; Kelleher & Bartlett, 1983; Millette et al., 1996).
While the 1978 Navy study provided the first thorough collection of data on airborne fiber expo-sure associated with gasket operations in a shipyard setting, it is uncertain how background airborneconcentrations of asbestos and nonasbestos fibers (i.e., contamination of the worksite due to asbestosinsulation) may have influenced the results because background samples of the workplace were notcollected. Further, the analytical method utilized by the Navy did not distinguish between asbestosfibers and other nonasbestos fibers or particles of similar morphology. Because of these issues, it islikely that the results of the Navy study significantly overestimated exposure to airborne asbestos fibersdue to gasket activities.
Measurements associated with different gasket formation techniques in the Navy study resultedin a wide range of measured airborne fiber concentrations, from below the limit of detection to 0.3f/cc for several manual techniques (range of averages 0.07–0.13 f/cc, Table 2) and from below thelimit of detection to 1.3 f/cc for workshop techniques (range of averages <0.05–0.9 f/cc, Table 3). TheNavy reported one measurement of 5 f/cc associated with the use of a machine punch and 3 f/cc dur-ing use of a hand punch. These samples appear to be outliers. Even so, the average of all samplescollected during gasket formation (including the 3 f/cc and 5 f/cc measurements), was 0.29 f/cc,well below the contemporaneous exposure limits.
Gasket removal and installation produced lower and less variable measurements of airbornefibers, ranging from below the limit of detection to 0.39 f/cc (Tables 4 and 5). The average of all
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TABL
E 2.
Repo
rted
Tim
e-W
eigh
ted
Ave
rage
(TW
A) A
irbor
ne F
iber
Con
cent
ratio
ns E
ncou
nter
ed b
y W
orke
rs: G
aske
t For
mat
ion
from
Asb
esto
s G
aske
t She
ets
Usin
g H
and-
Hel
d To
ols
Brea
thin
g zo
ne c
once
ntra
tion
of fi
ber
(f/cc
)
PCM
Stud
yG
aske
ts
form
ed (n
)G
aske
t for
mat
ion
met
hod
Asbe
stos
co
nten
t (%
)aA
vera
geb
Rang
eSD
nBa
ckgr
ound
con
c.(P
CM
) (f/c
c)A
ppro
x. s
ampl
edu
ratio
n (m
in)
Shor
t-te
rm p
erso
nal s
ampl
es (a
ctiv
ity o
nly)
Nav
yc,d
NR
Han
d sh
apin
g w
/ kni
ves,
scr
ibes
, sci
ssor
se,f
NR
0.13
<0.
03–0
.30.
1010
—7–
30N
avyc,
dN
RH
and
punc
he,g
NR
0.07
<0.
05–0
.15
0.04
6—
30Sp
ence
r9
Ball
peen
ham
mer
, han
d sh
ears
& s
crib
e50
–60
<0.
045
——
2<
0.00
230
Ove
rall
Ave
rage
0.10
Long
-ter
m p
erso
nal s
ampl
es (8
-h)
Man
gold
et a
l.8
Circ
ular
cut
ter
−80
0.00
5—
—1
<0.
002
480
Man
gold
et a
l.8
Han
d sh
ears
700.
005
——
1<
0.00
248
0M
ango
ld e
t al.
8Ba
ll pe
en h
amm
er70
0.00
5—
—1
<0.
002
480
Man
gold
et a
l.16
Scrib
e70
0.00
5—
—1
<0.
002
480
Che
ng a
nd M
cDer
mot
tN
RKn
ife o
n le
ad ta
ble
NR
0.01
2—
—1
<0.
002
490
Spen
cer
8H
and
shea
rs50
–60
0.00
6N
RN
R2
<0.
002
480
Spen
cer
8Po
cket
kni
fe50
–60
0.00
4N
RN
R2
<0.
002
480
Spen
cer
8Ba
ll pe
en h
amm
er50
–60
0.00
5N
RN
R2
<0.
002
480
Spen
cer
8Sc
ribe/
circ
ular
cut
ter
50–6
00.
008
NR
NR
2<
0.00
248
0Sp
ence
r9
Ballp
een
ham
mer
, han
d sh
ears
, and
scr
ibe
50–6
0<
0.00
8N
RN
R2
<0.
002
480
Boel
ter e
t al.c,
h8
Mar
itim
e—ba
llpee
n ha
mm
er60
–80
0.02
60.
022–
0.02
90.
005
2<
7048
0Bo
elte
r et a
l.c,h
8In
dust
rial—
ballp
een
ham
mer
60–8
00.
045
0.03
8–0.
052
0.01
02
<70
480
Ove
rall
Ave
rage
0.01
2
Not
e. n
, Num
ber o
f sam
ples
; PC
M, p
hase
-con
trast
mic
rosc
opy;
TEM
, tra
nsm
issio
n el
ectro
n m
icro
scop
y; N
R, n
ot r
epor
ted;
SD
, sta
ndar
d de
viat
ion;
f/cc
, fib
ers
per
cubi
c ce
ntim
eter
; TW
A,tim
e-w
eigh
ted
aver
age;
—, n
ot a
pplic
able
. In
stud
ies t
hat d
id n
ot re
port
mea
n co
ncen
trat
ion
or st
anda
rd d
evia
tion,
thes
e va
lues
wer
e ca
lcul
ated
from
ava
ilabl
e da
ta u
sing
one
half
the
limit
ofde
tect
ion
for c
alcu
latio
ns in
volv
ing
sam
ples
bel
ow th
e lim
it of
det
ectio
n. A
ny v
alue
s th
at a
re n
ot re
port
ed a
s ar
ithm
etic
mea
ns o
r sta
ndar
d de
viat
ions
are
not
ed a
ppro
pria
tely
.a A
ll as
best
os-c
onta
inin
g ga
sket
s co
ntai
ned
chry
sotil
e as
best
os o
nly.
b Aver
age
conc
entra
tion
repr
esen
ts th
e ac
tivity
TW
A fo
r the
per
form
ed ta
sk in
the
activ
ity s
tudi
es a
nd th
e 8-
h TW
A fo
r the
per
form
ed ta
sk in
the
8-h
stud
ies.
c Ave
rage
s an
d/or
sta
ndar
d de
viat
ion
valu
es a
re c
alcu
late
d fro
m a
vaila
ble
data
repo
rted
by s
tudy
aut
hors
.d A
vera
ges
repo
rted
by s
tudy
incl
uded
non
dete
ctab
le v
alue
s at
lim
it of
det
ectio
n; s
tand
ard
devi
atio
ns w
ere
calc
ulat
ed fr
om re
port
ed d
ata,
incl
udin
g no
ndet
ecta
ble
mea
sure
men
ts a
t lim
it of
dete
ctio
n.e H
ouse
keep
ing
defin
ed a
s th
e us
e of
vac
uum
s (P
orto
vacs
), pu
tting
was
te m
ater
ial i
n se
aled
con
tain
ers,
kee
ping
are
a cl
ean
of d
ebris
.f A
ctiv
ity c
ondu
cted
with
out h
ouse
keep
ing
proc
edur
es.
g Activ
ity c
ondu
cted
with
hou
seke
epin
g pr
oced
ures
.h Ba
ckgr
ound
dat
a pr
esen
ted
as s
/mm
2 .
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uly
2007
270
TABL
E 3.
Repo
rted
Tim
e-W
eigh
ted
Aver
age
(TW
A) A
irbor
ne F
iber
Con
cent
ratio
ns E
ncou
nter
ed b
y W
orke
rs:
Gas
ket
Form
atio
n fro
m R
olle
d As
best
os G
aske
t Sh
eets
Usin
g W
orks
hop
Tool
sAl
one
or in
Con
junc
tion
With
Han
d-H
eld
Tool
s
Brea
thin
g zo
ne fi
ber c
once
ntra
tion
(f/
cc)
PCM
Stud
yG
aske
ts fo
rmed
(n)
Gas
ket f
orm
atio
n m
etho
dAs
best
osC
onte
nt (%
)aA
vera
geb
Rang
eSD
nBa
ckgr
ound
con
c.(P
CM
) (f/c
c)Ap
prox
. sam
ple
dura
tion
(min
)
Shor
t-te
rm p
erso
nal s
ampl
es (a
ctiv
ity o
nly)
Nav
ycN
RH
and
oper
ated
mec
hani
cal p
unch
eN
R<
0.05
<0.
050.
008
—30
Nav
ycN
RM
achi
ne s
hear
sd,e
NR
0.9
0.5–
1.3
2.62
2—
6N
avyc
NR
Mac
hine
she
arsd,
fN
R0.
070.
05–0
.15
0.04
6—
35N
avyc,
gN
RM
achi
ne n
ibbl
erd,
eN
R0.
26<
0.08
–0.4
60.
272
—8
Nav
ycN
RM
achi
ne n
ibbl
erd,
fN
R0.
420.
08–0
.80.
268
—30
Nav
yc,g
NR
Mac
hine
pun
chd,
fN
R0.
19<
0.03
–0.7
10.
2112
—30
Nav
yc,g
NR
Mac
hine
pun
chd,
fN
R<
0.05
<0.
05–0
.06
0.00
8—
30C
heng
and
McD
erm
ottc
NR
Sabe
r saw
NR
0.36
0.33
–0.3
90.
042
—55
Che
ng a
nd M
cDer
mot
tcN
RPo
wer
she
ar a
nd w
heel
cut
ter
NR
0.42
0.34
–0.4
90.
112
—30
Fow
lerc
NR
Band
saw
802.
652.
2–3.
10.
642
—30
Fow
lerc
NR
Band
saw
804.
003.
1–4.
91.
272
—7–
8Ye
ung
et a
l.N
RH
and-
held
saw
and
sta
mpi
ng
mac
hine
NR
<0.
05<
0.05
—2
—10
0
Ove
rall
Ave
rage
0.42
Long
-ter
m p
erso
nal s
ampl
es (8
-h)
Che
ng a
nd M
cDer
mot
tN
RW
heel
cut
ter a
nd h
amm
er p
unch
NR
0.00
3—
—1
—46
5C
heng
and
McD
erm
ott
NR
Pow
er s
hear
and
whe
el c
utte
rN
R0.
017
——
1—
408
Che
ng a
nd M
cDer
mot
tN
RPo
wer
she
ar a
nd s
ciss
ors
NR
0.00
1—
—1
—47
0C
heng
and
McD
erm
ott
NR
Pow
er s
hear
and
ham
mer
pun
chN
R0.
015
——
1—
330
Che
ng a
nd M
cDer
mot
tN
RPo
wer
she
ar a
nd h
amm
er p
unch
NR
0.00
9—
—1
—34
4C
heng
and
McD
erm
ott
NR
Pow
er s
hear
and
ham
mer
pun
chN
R0.
005
——
1—
359
Ove
rall
Ave
rage
0.00
8
Not
e. N
, Num
ber o
f sam
ples
; PC
M, p
hase
-con
trast
mic
rosc
opy;
TEM
, tra
nsm
issio
n el
ectro
n m
icro
scop
y; N
R, n
ot re
port
ed; S
D, s
tand
ard
devi
atio
n; f/
cc, f
iber
s pe
r cub
ic c
entim
eter
; TW
A,tim
e-w
eigh
ted
aver
age;
—, n
ot a
pplic
able
. In
stud
ies t
hat d
id n
ot re
port
mea
n co
ncen
trat
ion
or s
tand
ard
devi
atio
n, th
ese
valu
es w
ere
calc
ulat
ed fr
om a
vaila
ble
data
usin
g on
e ha
lf th
e lim
it of
dete
ctio
n fo
r cal
cula
tions
invo
lvin
g sa
mpl
es b
elow
the
limit
of d
etec
tion.
Any
val
ues
that
are
not
repo
rted
as
arith
met
ic m
eans
or s
tand
ard
devi
atio
ns a
re n
oted
app
ropr
iate
ly.
a All
asbe
stos
-con
tain
ing
gask
ets
cont
aine
d ch
ryso
tile
asbe
stos
onl
y.b Av
erag
e co
ncen
tratio
n re
pres
ents
the
activ
ity T
WA
for t
he p
erfo
rmed
task
in th
e ac
tivity
stu
dies
and
the
8-h
TWA
for t
he p
erfo
rmed
task
in th
e 8-
h st
udie
s.c A
vera
ge a
nd/o
r sta
ndar
d de
viat
ion
valu
es a
re c
alcu
late
d fro
m a
vaila
ble
data
repo
rted
by s
tudy
aut
hors
.d H
ouse
keep
ing
defin
ed a
s th
e us
e of
vac
uum
s (P
orto
vacs
), pu
tting
was
te m
ater
ial i
n se
aled
con
tain
ers,
kee
ping
are
a cl
ean
of d
ebris
.e Ac
tivity
con
duct
ed w
ithou
t hou
seke
epin
g pr
oced
ures
.f A
ctiv
ity c
ondu
cted
with
hou
seke
epin
g pr
oced
ures
.g Av
erag
es r
epor
ted
by s
tudy
incl
uded
non
dete
ctab
le v
alue
s at
lim
it of
det
ectio
n; s
tand
ard
devi
atio
ns w
ere
calc
ulat
ed fr
om re
port
ed d
ata
incl
udin
g no
ndet
ecta
ble
mea
sure
men
ts a
t lim
it of
dete
ctio
n.
Dow
nloa
ded
By:
[LaB
oon,
Joh
n] A
t: 14
:18
17 J
uly
2007
271
TABL
E 4.
Repo
rted
Tim
e-W
eigh
ted
Aver
age
(TW
A)
Airb
orne
Fib
er C
once
ntra
tions
Enc
ount
ered
by
Wor
kers
: Re
mov
al o
f D
ry G
aske
ts a
nd F
lang
e Fa
ce C
lean
ing
Usin
g H
and
Scra
pers
and
Wire
Bru
shes
Brea
thin
g zo
ne fi
ber c
once
ntra
tion
(f/
cc)
PCM
Stud
yG
aske
tsre
mov
ed (n
)G
aske
t rem
oval
and
flan
ge
clea
ning
met
hod
Asb
esto
s co
nten
t (%
)aA
vera
geb
Rang
eSD
nBa
ckgr
ound
co
nc. (
f/cc)
Appr
ox. s
ampl
edu
ratio
n (m
in)
Shor
t-te
rm p
erso
nal s
ampl
es (a
ctiv
ity o
nly)
Nav
yc,d
NR
Rem
oval
and
wire
bru
shin
gN
R0.
11<
0.03
–0.1
80.
078
—25
–33
Nav
yc,d
NR
Rem
oval
and
han
d sc
rapi
nge
NR
0.13
<0.
03–0
.39
0.11
14—
15–3
0N
avyc
NR
Han
d sc
rapi
ng o
nly
(no
rem
oval
)N
R<
0.05
<0.
050.
004
—33
–36
Che
ng a
nd M
cDer
mot
t2
Scra
ping
and
bru
shin
g va
lve
gask
etN
R0.
11—
—1
—19
Che
ng a
nd M
cDer
mot
t1
Scra
ping
and
bru
shin
g pu
mp
gask
etN
R0.
19—
—1
—46
Che
ng a
nd M
cDer
mot
t 2
Scra
ping
and
bru
shin
g fla
nge
gask
etN
R0.
33—
—1
—55
McK
inne
ry a
nd M
oore
fN
RN
R50
–60
0.16
0.05
–0.4
41.
9123
—32
Long
o et
al.
10Sc
rapi
ng a
nd b
rush
ing
smal
l gas
kets
65
–85
3.7
1.5
– 10
.1N
R14
0.0
10–1
5Lo
ngo
et a
l.4
Scra
ping
and
bru
shin
g la
rge
gask
ets
65–8
515
.39.
3 –
24.0
NR
100.
010
–15
Ove
rall
Ave
rage
(with
Lon
go)
2.79
Ove
rall
Ave
rage
(with
out L
ongo
)0.
14Lo
ng-t
erm
per
sona
l sam
ples
(8-h
)M
ango
ld e
t al.c
4G
aske
t rem
oval
and
scr
apin
gN
R0.
030.
01–0
.08
0.02
120
0.00
2–0.
005
480
Man
gold
et a
l.c6
Gas
ket r
emov
al a
nd s
crap
ing
NR
0.02
30.
01–0
.05
0.01
310
0.00
2–0.
004
480
Man
gold
et a
l.8
Han
d sc
rapi
ng w
ith p
utty
kni
fe60
–80
<0.
005
——
1<
.002
480
Man
gold
et a
l.8
Han
d-w
ire b
rush
ing
60–8
00.
007
——
1<
.002
480
Boel
ter e
t al.c,
g8
Indu
stria
l—Fl
at b
lade
scr
apin
g40
–80
0.03
10.
028–
0.03
50.
0049
2<
7048
0Bo
elte
r et a
l.c,g
8M
ariti
me—
Flat
bla
de s
crap
ing
40–8
00.
017
0.01
4–0.
019
0.00
352
<70
480
Boel
ter e
t al.c,
g8
Indu
stria
l—H
and
wire
bru
shin
g40
–80
0.00
60.
005–
0.00
70.
0014
2<
7048
0Bo
elte
r et a
l.c,g
8M
ariti
me—
Han
d w
ire b
rush
ing
40–8
00.
002
0.00
0–0.
004
0.00
282
<70
480
Ove
rall
Ave
rage
0.02
4
Not
e. N
, Num
ber o
f sam
ples
; PC
M, p
hase
-con
trast
mic
rosc
opy;
TEM
, tra
nsm
issio
n el
ectro
n m
icro
scop
y; N
R, n
ot re
port
ed; S
D, s
tand
ard
devi
atio
n; f/
cc, f
iber
s pe
r cub
ic c
entim
eter
; TW
A,tim
e w
eigh
ted
aver
age;
— n
ot a
pplic
able
. In
stud
ies
that
did
not
repo
rt m
ean
conc
entra
tion
or s
tand
ard
devi
atio
n, th
ese
valu
es w
ere
calc
ulat
ed fr
om a
vaila
ble
data
usin
g on
e ha
lf th
e lim
it of
dete
ctio
n fo
r cal
cula
tions
invo
lvin
g sa
mpl
es b
elow
the
limit
of d
etec
tion.
Any
val
ues
that
are
not
repo
rted
as
arith
met
ic m
eans
or s
tand
ard
devi
atio
ns a
re n
oted
app
ropr
iate
ly.
a All
asbe
stos
-con
tain
ing
gask
ets
cont
aine
d ch
ryso
tile
asbe
stos
onl
y.b Av
erag
e co
ncen
tratio
n re
pres
ents
the
activ
ity T
WA
for t
he p
erfo
rmed
task
in th
e ac
tivity
stu
dies
and
the
8-h
TWA
for t
he p
erfo
rmed
task
in th
e 8-
h st
udie
s.c A
vera
ge a
nd/o
r sta
ndar
d de
viat
ion
valu
es a
re c
alcu
late
d fro
m a
vaila
ble
data
repo
rted
by s
tudy
aut
hors
.d Av
erag
es re
port
ed b
y st
udy
incl
uded
non
dete
ctab
le v
alue
s at
lim
it of
det
ectio
n; s
tand
ard
devi
atio
ns w
ere
calc
ulat
ed fr
om re
porte
d da
ta in
clud
ing
nond
etec
tabl
e m
easu
rem
ents
at l
imit
ofde
tect
ion.
e Perfo
rmed
with
out h
ouse
keep
ing;
Hou
seke
epin
g de
fined
as
the
use
of v
acuu
ms
(Por
tova
cs),
putti
ng w
aste
mat
eria
l in
seal
ed c
onta
iner
s, k
eepi
ng a
rea
clea
n of
deb
ris.
f Ave
rage
val
ue re
pres
ents
the
geom
etric
mea
n; s
tand
ard
devi
atio
n va
lue
repr
esen
ts th
e ge
omet
ric s
tand
ard
devi
atio
n.g Ba
ckgr
ound
dat
a pr
esen
ted
as s
/mm
2 .
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272
TABL
E 5.
Repo
rted
Tim
e-W
eigh
ted
Aver
age
(TW
A) A
irbor
ne F
iber
Con
cent
ratio
ns E
ncou
nter
ed b
y W
orke
rs: G
aske
t Rem
oval
(Wet
and
Dry
) and
Inst
alla
tion
and
Flan
ge F
ace
Cle
anin
g U
sing
Pow
er T
ools
Brea
thin
g zo
ne fi
ber c
once
ntra
tion
(f/cc
)
PCM
Stud
yG
aske
ts
rem
oved
(N)
Gas
ket r
emov
al a
nd fl
ange
cl
eani
ng m
etho
dA
sbes
tos
cont
ent (
%)a
Ave
rage
bRa
nge
SDn
Back
grou
nd c
onc.
(PC
M) (
f/cc)
App
rox.
sam
ple
dura
tion
(min
)
Dry
gas
ket r
emov
alW
ith fl
ange
cle
anin
g us
ing
pow
er m
achi
nery
Shor
t-te
rm p
erso
nal s
ampl
es (a
ctiv
ity o
nly)
Che
ng a
nd M
cDer
mot
t2
Pow
er s
ande
r on
flang
e ga
sket
sN
R1.
4—
—1
—25
Long
o et
al.
1Po
wer
wire
bru
shin
g fla
nges
65–8
521
.814
.9–3
1.0
NR
70.
1142
Ove
rall
Aver
age
(with
Lon
go)
19.3
Ove
rall
Aver
age
(with
out L
ongo
)1.
4
Long
-ter
m p
erso
nal s
ampl
es (8
-h)
Man
gold
et a
l.8
Pow
er w
ire b
rush
ing
flang
es60
–80
0.00
9—
—1
<0.
002
480
Boel
ter e
t al.c
8In
dust
rial—
Pow
er w
ire b
rush
ing
40–8
00.
022
0.02
1–0.
023
0.00
142
<70
480
Boel
ter e
t al.c
8M
ariti
me—
Pow
er w
ire b
rush
ing
40–8
00.
009
0.00
8–0.
010
0.00
142
<70
480
Ove
rall
Ave
rage
0.01
4W
ith in
stal
l and
no
flang
e cl
eani
ngSh
ort-
term
per
sona
l sam
ples
(act
ivity
onl
y)N
avyc
NR
(with
hou
seke
epin
g)d
NR
0.09
0.02
–0.3
0.06
429
—20
–95
Spen
cer
8—
50–6
0<
0.04
5—
—1
<0.
002
30O
vera
ll A
vera
ge0.
088
Long
-ter
m p
erso
nal s
ampl
es (8
-h)
Man
gold
et a
l.c,e
NR
—N
R0.
005
<0.
004–
0.00
50.
04
—24
0Sp
ence
r8
—50
–60
0.01
5N
RN
R2
<0.
002
480
Ove
rall
Ave
rage
0.00
8
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273
With
inst
all a
nd fl
ange
cle
anin
gLo
ng-t
erm
per
sona
l sam
ples
(8-h
)Sp
ence
r4
Scra
pe, h
and
wire
bru
sh50
–55
0.00
5N
RN
R2
<0.
002
480
Spen
cer
4Sc
rape
, pow
er w
ire b
rush
50–5
50.
005
NR
NR
2<
0.00
248
0O
vera
ll A
vera
ge0.
005
Dry
gas
ket i
nsta
ll on
ly (n
o fla
nge
clea
ning
)Sh
ort-
term
per
sona
l sam
ples
(act
ivity
onl
y)N
avyc
NR
—N
R<
0.03
<0.
030.
04
—30
McK
inne
ry a
nd M
oore
f,gN
R—
50–6
00.
200.
13–0
.29
1.28
12—
31O
vera
ll A
vera
ge0.
154
Wet
gas
ket r
emov
al—
activ
ity a
nd 8
-h d
aySh
ort-
term
per
sona
l sam
ples
(act
ivity
onl
y)C
heng
and
McD
erm
ott
1Sc
rapi
ng/b
rush
ing
pum
p ga
sket
NR
<0.
06—
—1
—30
Che
ng a
nd M
cDer
mot
t2
Brus
hing
pip
e fla
nge
gask
etN
R<
0.06
——
1—
15Sp
ence
and
Roc
chig
51Sc
rapi
ng ti
ghtly
adh
ered
gas
kets
NR
—N
D–0
.025
—10
—69
–156
Ove
rall
Ave
rage
0.03
Long
-ter
m p
erso
nal s
ampl
es (8
-h)
Spen
ce a
nd R
occh
ic,g
50Sc
rapi
ng e
asily
rem
oved
gas
kets
NR
0.08
50.
042–
0.24
20.
060
11—
400–
435
Ove
rall
Ave
rage
0.08
5
Not
e. n
, Num
ber o
f sam
ples
; PC
M, p
hase
-con
trast
mic
rosc
opy;
TEM
, tra
nsm
issio
n el
ectro
n m
icro
scop
y; N
R, n
ot re
porte
d; S
D, s
tand
ard
devi
atio
n; f/
cc, f
iber
s per
cub
ic c
entim
eter
; ND
, non
-de
tect
; TW
A, ti
me-
wei
ghte
d av
erag
e; —
, not
app
licab
le. I
n st
udie
s tha
t did
not
repo
rt m
ean
conc
entra
tion
or st
anda
rd d
evia
tion,
thes
e va
lues
wer
e ca
lcul
ated
from
ava
ilabl
e da
ta u
sing
one
half
the
limit
of d
etec
tion
for c
alcu
latio
ns in
volv
ing
sam
ples
bel
ow th
e lim
it of
det
ectio
n. A
ny v
alue
s tha
t are
not
repo
rted
as a
rithm
etic
mea
ns o
r sta
ndar
d de
viat
ions
are
not
ed a
ppro
pria
tely
.a A
ll as
best
os-c
onta
inin
g ga
sket
s co
ntai
ned
chry
sotil
e as
best
os o
nly.
b Aver
age
conc
entra
tion
repr
esen
ts th
e ac
tivity
TW
A fo
r the
per
form
ed ta
sk in
the
activ
ity s
tudi
es a
nd th
e 8-
h TW
A fo
r the
per
form
ed ta
sk in
the
8-h
stud
ies.
c Ave
rage
and
/or s
tand
ard
devi
atio
n va
lues
are
cal
cula
ted
from
ava
ilabl
e da
ta re
porte
d by
stu
dy a
utho
rs.
d Hou
seke
epin
g de
fined
as
the
use
of v
acuu
ms
(Por
tova
cs),
putti
ng w
aste
mat
eria
l in
seal
ed c
onta
iner
s, k
eepi
ng a
rea
clea
n of
deb
ris.
e Activ
ities
repe
ated
with
a fr
eque
ncy
repo
rted
equi
vale
nt to
an
8-h
wor
kday
.f A
vera
ge v
alue
repr
esen
ts th
e ge
omet
ric m
ean;
sta
ndar
d de
viat
ion
valu
e re
pres
ents
the
geom
etric
sta
ndar
d de
viat
ion.
g All g
aske
ts c
onta
ined
asb
esto
s, b
ut th
e pe
rcen
tage
s w
ere
not r
epor
ted.
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274 A. K. MADL ET AL.
samples collected during all gasket removal and installation activities was 0.09 f/cc (n=58; averagecalculated by authors). Wire brushes and hand scrapers were the tools used to remove adhered gas-kets, but the authors of the Navy study did not specify whether it was hand or power wire brushing.Because hand wire brushes were more commonly used than power brushes, it was assumed for thepurpose of our analysis that, unless specified, hand wire brushes were used. Most of the samples inthis study were collected for approximately 30 min.
The Navy study reported a broader range of concentrations during gasket removal than thosereported in the simulation studies. The samples collected without the use of general housekeepingoften resulted in concentrations that were orders of magnitude higher than results for comparabletasks conducted when housekeeping measures were used. The housekeeping techniques were rel-atively basic; they involved routine cleanup of asbestos-containing materials in the work area, butdid not include local exhaust ventilation, which is the most effective method of reducing airbornefiber concentrations. Therefore, based on the data presented in the Navy study, it appears that sim-ple precautionary procedures could significantly reduce the magnitude of exposure to airbornefibers. Without any data on background concentrations (samples collected prior to gasket work), itis impossible to evaluate how much of the exposure was attributable to actual gasket activities orthe degree to which housekeeping reduced contamination prior to the onset of any work.
The data from the Navy study, although groundbreaking at the time, characterizes the airbornefiber exposures experienced in a shipyard or onboard a ship and is not specifically related to thepossible exposures created by specific products. As a result, it can be assumed that the data repre-sent worst case scenarios attributable to gaskets and packings.
Work-Site StudiesFour work-site studies are addressed in this analysis: the U.S. Navy study (Liukonen et al., 1978)
and the studies by Cheng and McDermott (1991), Spence and Rocchi (1996), and Yeung et al.(1999). The Cheng and McDermott study was performed at a chemical plant and, similar to theU.S. Navy study, background samples were not collected at the worksite prior to the onset of thestudy. Airborne fiber exposures associated with gasket formation were characterized from 7 long-term (>300 min) and 4 short-term (<60 min) samples. Airborne fiber concentrations associatedwith gasket removal and flange surface cleaning were based on the collection of six short-termsamples (<60 min). Two of the short-term samples were collected during gasket removal and sur-face cleaning using wet gasket removal techniques. The average of the long-term exposures duringgasket formation was 0.008 f/cc, with data ranging from 0.001 to 0.017 f/cc (average calculated byauthors; Table 3). The short-term concentrations collected during dry gasket removal and formationranged from 0.11 to 1.4 f/cc (Tables 3–5), the onset of the study both of the samples taken duringwet gasket removal were below the limit of detection. The authors concluded that potential expo-sures can be controlled by wetting the gasket and the seating surfaces prior to gasket replacement(Cheng & McDermott, 1991). They recommended that a half-face HEPA respirator be providedto workers as a precautionary measure (Cheng & McDermott, 1991). The primary shortcomings ofthis study were that the analytical methods were not described, background samples were not col-lected, and results from any bulk sample analyses to determine whether the gaskets actually con-tained asbestos were not reported.
The work-site study by Spence and Rocchi (1996) was conducted at a chemical plant in theNetherlands. Unlike the other work-site studies, it focused exclusively on wet gasket removal. Theauthors divided the gaskets into two categories, those that came off easily without breaking andthose that needed additional effort to remove. Eleven long-term samples (≥400 min) were collectedin the study while workers removed gaskets that were easily removed, and ten short-term samples(<160 min) were taken while workers removed more adhered gaskets. While no background sam-ples were collected, the authors did perform bulk sample analysis of the removed gaskets. As indi-cated by PCM analysis, the average of long-term airborne concentrations was 0.085 f/cc, with dataranging from 0.042 to 0.242 f/cc (average calculated by authors; Table 5). The TEM data rangedfrom nondetectable to 0.0014 f/cc. Nearly half of the short-term samples were below the limit ofdetection by PCM analysis, with concentrations ranging from nondetectable to 0.025 f/cc (Table 5).
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ASBESTOS-CONTAINING GASKETS AND PACKINGS 275
Only one of the three short-term samples analyzed by TEM analysis had detectable asbestos fibers(0.0037 f/cc). Spence and Rocchi (1996) concluded that using a suitable wetting agent providesadequate protection of the employee and that PCM analysis may not be applicable where mixedfibers are present, which may have resulted in an overestimation of the asbestos fiber concentrationin this study. Their data also showed that the PCM analysis detected fibers when the gasket beingremoved did not contain asbestos.
The study by Yeung and colleagues (1999) measured airborne chrysotile exposures to workersin the automotive service industry, which included industrial hygiene assessments of nine servicefacilities and workshops. One workshop assessed in this study was a gasket processing workshopwhere asbestos gaskets were formed from compressed asbestos fiber sheets by hand-held electricsaws and were cut with a powered stamping machine. Air samples during cutting and stampingoperations showed airborne fiber concentrations below 0.05 f/cc (Yeung et al. 1999).
Simulation StudiesEighteen individual simulation studies were identified for this analysis, 11 of which were per-
formed by Carl Mangold and two of which were performed by John Spencer (Spencer, 1998a,1998b; Mangold et al., 2006). The others were performed by McKinnery and Moore (1992), Mil-lette and Mount (1993), Fowler (2000), Longo et al. (2003), and Boelter et al. (2002). The benefit ofsimulation studies is that the confounding variables of workplace studies are not present; thus, ifconducted properly, they should be better descriptors of the exposure for a particular task than tra-ditional industrial hygiene studies.
McKinnery and Moore (1992) performed a simulation study on airborne fiber exposures associ-ated with the removal and installation of asbestos packing and gaskets. This study was conducted inan isolated room on valves that were obtained from industrial facilities. The work was performed bya licensed asbestos worker under the supervision of a union pipefitter. The report provided limitedinformation on background fiber concentrations, number of valves worked on, whether the valveswere cleaned prior to the study, sampling times, and methods of analysis. Several samples were col-lected to characterize airborne fiber exposures during the removal and installation of gaskets. Thegeometric means of the breathing zone PCM data during packing removal and installation were0.29 f/cc and 0.10 f/cc, respectively (Table 6). During gasket removal and installation, the geometricmeans of the PCM data were 0.16 f/cc and 0.20 f/cc, respectively (Tables 4 and 5). The TEM datawere reported for structures of all sizes, which is not consistent with the NIOSH classification ofasbestos fibers (greater than 5 μm in length). The TEM data indicated breathing zone concentrationsranging from 0.07 to 19.57 s/cc during packing activities and 0.40 to 74.32 s/cc during gasket activities.
Millette and Mount performed a study in 1993 characterizing exposures associated with theremoval of packing materials (Millette & Mount, 1993). This study took place in a contaminant-freeisolation chamber, in which packing materials were removed from pre-cleaned valves obtainedfrom a power plant. The authors analyzed air samples by NIOSH methods 7400 and 7402. Whilethree packing removal activities were characterized in this study, it is not clear whether the packingmaterials were removed from two or three valves. Two breathing zone samples were collected dur-ing each packing removal activity, all of which were analyzed by PCM. The average concentrationof the 5 samples analyzed by PCM was 0.72 f/cc, with individual measurements ranging from 0.2 f/ccto 1.3 f/cc (calculated by authors; Table 6). TEM analysis was performed on the samples from thelast 2 packing removal activities, and the reported breathing zone concentrations ranged from 1.2to 2.6 f/cc with an average of 1.7 f/cc (calculated by authors).
Spencer (1998a, 1998b) performed two unpublished work-site simulation studies on the forma-tion of gaskets and the removal and installation of gaskets and packing materials. In these studies,airborne concentrations associated with gasket formation techniques were characterized for fiveworkdays, gasket installation on one day, the combined removal and installation of gaskets for threedays, and removal and installation of packing materials for two days. All of the work was conductedby a skilled tradesman and took place in isolation chambers that were cleaned prior to each activ-ity. Eight area, two worker, two assistant, and two outdoor background samples for airborne fiberswere collected over the course of the day rather than taken separately for each occurrence of the
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TABL
E 6.
Repo
rted
Tim
e-W
eigh
ted
Ave
rage
(TW
A) A
irbor
ne F
iber
Con
cent
ratio
ns E
ncou
nter
ed b
y W
orke
rs: R
emov
al a
nd In
stal
latio
n of
Asb
esto
s Pa
ckin
g
Brea
thin
g zo
ne fi
ber c
once
ntra
tion
(f/cc
)
PCM
Stud
yPa
ckin
gRe
mov
ed (n
)Si
te o
f pa
ckin
gA
sbes
tos
cont
ent (
%)a
Aver
ageb
Rang
eSD
nBa
ckgr
ound
conc
. (f/c
c)A
ppro
x. sa
mpl
e du
ratio
n (m
in)
Pack
ing
rem
oval
onl
ySh
ort-
term
per
sona
l sam
ples
(act
ivity
onl
y)M
cKin
nery
and
Moo
rec
NR
Valv
es30
–50
0.29
0.05
–1.0
12.
2821
—46
Mill
ette
and
Mou
ntd
3Va
lves
850.
720.
2–1.
30.
445
0.00
6–0.
009
25–3
3O
vera
ll A
vera
ge0.
37Pa
ckin
g re
mov
al a
nd in
stal
latio
nLo
ng-t
erm
per
sona
l sam
ples
(8-h
)M
ango
ld8
Val
ves
70<
0.01
1—
—1
0.00
225
5Sp
ence
rd4
Valv
esRe
mov
ed: 6
0–90
In
stal
led:
75
0.01
5—
—2
0.00
448
0
Spen
cerd
4Va
lves
Rem
oved
: 60–
90
Inst
alle
d: 7
0–90
0.01
0—
—2
0.00
248
0
Boel
ter e
t al.d,
e8
Valv
esRe
mov
ed: 4
0–80
In
stal
led:
80
0.02
60.
024–
0.02
70.
0021
2<
7048
0
Boel
ter e
t al.d,
e8
Valv
esRe
mov
ed: 4
0–80
In
stal
led:
80
0.00
90.
008–
0.01
00.
0014
2<
7048
0
Ove
rall
Ave
rage
0.01
4Pa
ckin
g in
stal
latio
n on
lySh
ort-
term
per
sona
l sam
ples
(act
ivity
onl
y)M
cKin
nery
and
Moo
rec
NR
Valv
es30
–50
0.10
0.04
–0.5
22.
2118
—26
Ove
rall
Ave
rage
0.10
Not
es. N
, Num
ber o
f sam
ples
; PC
M, p
hase
-con
trast
mic
rosc
opy;
TEM
, tra
nsm
issio
n el
ectro
n m
icro
scop
y; N
R, n
ot re
port
ed; S
D, s
tand
ard
devi
atio
n; f/
cc, f
iber
s per
cub
ic c
entim
eter
; TW
A,tim
e-w
eigh
ted
aver
age;
—no
t app
licab
le. I
n st
udie
s th
at d
id n
ot re
port
mea
n co
ncen
tratio
n or
sta
ndar
d de
viat
ion,
thes
e va
lues
wer
e ca
lcul
ated
from
ava
ilabl
e da
ta u
sing
one
half
the
limit
ofde
tect
ion
for c
alcu
latio
ns in
volv
ing
sam
ples
bel
ow th
e lim
it of
det
ectio
n. A
ny v
alue
s th
at a
re n
ot re
port
ed a
s ar
ithm
etic
mea
ns o
r sta
ndar
d de
viat
ions
are
not
ed a
ppro
pria
tely
.a A
ll as
best
os-c
onta
inin
g pa
ckin
g co
ntai
ned
chry
sotil
e as
best
os o
nly.
b Aver
age
conc
entra
tion
repr
esen
ts th
e ac
tivity
TW
A fo
r the
per
form
ed ta
sk in
the
activ
ity s
tudi
es a
nd th
e 8-
h TW
A fo
r the
per
form
ed ta
sk in
the
8-h
stud
ies.
c Aver
age
valu
e re
pres
ents
the
geom
etric
mea
n; S
tand
ard
devi
atio
n va
lue
repr
esen
ts th
e ge
omet
ric s
tand
ard
devi
atio
n.d A
vera
ge a
nd/o
r sta
ndar
d de
viat
ion
valu
es a
re c
alcu
late
d fro
m a
vaila
ble
data
repo
rted
by
stud
y au
thor
s.e Ba
ckgr
ound
dat
a pr
esen
ted
as s
/mm
2 .
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ASBESTOS-CONTAINING GASKETS AND PACKINGS 277
activity. Work activities were usually performed four to eight times over the course of the workday.Although individual sample data were not reported, the average personal 8-h TWAs were pre-sented. Short-term (30-min samples) were collected on the worker and helper during some of thegasket formation activities for comparison to the OSHA excursion limit for asbestos. Spencer’sreports do not specify the source of the valves being worked on or whether they were cleaned priorto the study. The author concluded that all of the activities created exposures less than the OSHA 8-hTWA of 0.1 f/cc, with the 8-h TWAs for each activity ranging from 0.004 f/cc (during gasket forma-tion with pocket knife) to 0.015 f/cc (during packing and gasket removal and installation; Tables 2,5 and 6). All of the short-term samples were <0.045 f/cc, well below the current OSHA excursionlimits of 1 f/cc during 30 min (Tables 2 and 5).
Fowler (2000) performed a study that characterized the airborne fiber concentrations associ-ated with the unique scenario of band-sawing compressed asbestos gasket material. Gaskets werenot actually formed, but the author used a band saw to cut rolled gasket sheets into small rectanglesthat could then be used to form gaskets (Fowler, 2000). It has been noted that gasket material israrely, if ever, cut with a band saw. Four personal samples and four area samples were collectedinside an isolation chamber during the band-sawing of the gasket material. No background sampleswere collected. All air samples were analyzed by PCM and some by TEM, although the report didnot indicate which specific analytical methods were utilized. The author concluded that the use ofbandsaws and similar machinery on asbestos sheet gasket materials could create significant airbornefiber exposures. The four short-term breathing zone samples ranged from 2.2 to 4.9 f/cc with anaverage of 3.33 f/cc (by PCM analysis; average calculated by authors; Table 3). TEM analysis of thesame samples indicated an average airborne concentration of 11.3 f/cc, with samples ranging from8.2 to 17.6 f/cc (>5 μm in length; average calculated by authors).
Boelter et al. (2002) conducted perhaps the most comprehensive simulation study published todate in the peer-reviewed literature on gasket and packing activities. The study was conducted overten days, with each day dedicated to a different type of gasket or packing activity. Five days werespent working with industrial precleaned fittings from a decommissioned powerhouse and the otherfive days with maritime precleaned fittings from decommissioned U.S. Navy destroyers. The studytook place in an isolation chamber, which was sampled prior to conducting the study to confirm theabsence of asbestos contamination. Work activities studied included packing replacement, gasketformation using a ballpeen hammer, and gasket removal using hand wire brushes, power wirebrushes, and flat blade scraping. Personal samples were collected over an 8-h workday consisting ofeight repetitions of each task. The authors did not report the actual task duration or make any state-ments regarding standard work practices. The authors analyzed the air samples by PCM accordingto NIOSH method 7400 and chose not to analyze the samples by TEM. Because of the controlledenvironment in which the study was conducted, it was assumed that all fibers detected were asbes-tos. The average data from the 8-h personal samples ranged from 0.002 f/cc (during handwirebrushing of flanges) to 0.045 f/cc (during the formation of gaskets using a ballpeen hammer; aver-ages calculated by authors; Tables 2, 4–6). The authors concluded that the rates of fiber release forold and new elastomeric asbestos-containing gaskets and impregnated asbestos packing materialsare insignificant even when the materials are manipulated dry.
Between 1982 and 1991, Carl Mangold performed a series of studies on gasket and packingactivities, including the formation of gaskets using various tools, the removal of gaskets and thecleaning of flange faces, and the replacement of valve packing. One of the studies in this series, per-formed in 1982, was excluded from this analysis because of the high and variable background con-centrations in the areas where the study took place (Mangold et al., 2006). This particular study wasconducted in work areas that were not cleaned prior to the study, and statistical analyses indicatedthat the background concentrations measured before the study took place were not significantlydifferent from the breathing zone concentrations measured during the activities (95% confidenceinterval). Therefore, the contribution to the airborne asbestos concentration from the work activitywas so low as not to be measurable.
Most of the activities in the Mangold series of studies were performed on valves and flangestaken from decommissioned naval ships. The studies duplicated many of the operations performed
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278 A. K. MADL ET AL.
in the Navy Bremerton study, but in an environment in which the background concentrations ofasbestos contamination were characterized (Mangold et al., 2006). Mangold used PCM analysis forall samples, using either NIOSH method 7400 or its predecessor, the NIOSH P&CAM 239 method.The average breathing-zone fiber concentrations during these activities ranged from <0.005 f/cc(during flange scraping with a putty knife) to 0.03 f/cc (during gasket removal with scraping; Tables2, 4–6). In each study, the 8-h TWA exposures to airborne fibers attributable to gaskets or packingwere a fraction of the contemporaneous 8-h TWA PEL.
In the study titled “Fiber Release During the Removal of Asbestos-Containing Gaskets: A WorkPractice Simulation,” Longo and colleagues (2002) reported average airborne fiber concentrationsassociated with the scraping and wire brushing of flanges. Personal samples were collected duringgasket removal by scraping and brushing small and large gaskets retrieved from a paper mill power-house. Longo et al. (2002) reported average breathing zone concentrations of 3.7 (n=14) and 15.3f/cc (n=10) for scraping and brushing small and large gaskets as measured by PCM, respectively(Table 4). TEM results for these activities ranged from 29.9 to 842.7 f/cc (n=14 for each scenario).Personal samples collected during power wire brushing flanges showed an average airborne fiberconcentration of 21.8 f/cc (n= 7, range 14.9–31 f/cc) as measured by PCM (Table 5). TEM resultsranged from 877.1 to 1636.1 f/cc (n=7) (Longo et al., 2002).
Several of the methods used in the Longo et al. (2002) study were not consistent with otheroccupational exposure evaluations of gasket work, making it difficult to compare these data tooccupational exposure limits or the data from the other exposure studies presented in this analysis.First, the sample filters were overloaded with dust and/or other debris, which interferes with boththe PCM and TEM analysis. Second, the environment in which the study was conducted was notcleaned prior to characterizing potential exposures during power wire brushing. This is a seriousshortcoming in the study given that the average background concentration in the chamber (0.11 f/cc)exceeded the current OSHA 8-h TWA PEL before the work started. Third, due to the overloading ofthe filters, the authors used an indirect preparation method for TEM analysis, which is known tooverestimate the fiber counts and is not approved by U.S. EPA AHERA or NIOSH methods (Boelteret al., 2003).
Longo and colleagues (2005) recently conducted a similar study on the removal of asbestos-containing gaskets from air conditioning compressors. The results from this study have not beenpublished and appear to be an outlier compared to the results reported by other researchers overthe last 30 years. As with his earlier study, Longo et al. (2003) used a hand scraper and pneumaticpower rotor abrasive pad for grinding to remove asbestos-containing gaskets from air conditioningcompressors flange surfaces. Personal samples collected during these activities showed airbornefiber concentrations ranging from 20.7 to 167.2 f/cc as measured by PCM. It should be noted thatthe highest concentrations represent testing where the gasket was not removed by the scraperprior to grinding. Although Longo et al. (2003) indicate that the air samples were measured bydirect methods and were not overloaded, it is unclear how much of the gasket was removed withthe scraper in each of the testing and how these activities compare to a realistic occupational set-ting. Other gasket studies which measure worker exposures during the use of power grinding toolsreport airborne fiber concentrations at least an order of magnitude lower than those noted in theLongo studies (Cheng & McDermott, 1991, Boelter et al. 2002, Spencer 1998b, Mangold et al.,2006).
Evaluation of Exposures Categorized by Activity
Gasket Formation Tables 2 and 3 present the data collected from worker breathing zonesduring gasket formation activities, including the use of punches, knives, shears, ballpeen hammers,circular cutters, and nibblers. Each activity is subdivided into categories for the use of handheld orworkshop tools, and short- or long-term sampling times. Relevant information such as backgroundconcentrations, number of gaskets formed throughout the sampling events, and asbestos content ofthe gasket stock are included.
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ASBESTOS-CONTAINING GASKETS AND PACKINGS 279
Formation of gaskets from rolled asbestos sheets using hand-held tools Seven studies (or seriesof studies in the case of Mangold and Spencer) evaluated the formation of gaskets from rolledasbestos sheets. The Navy (Liukonen et al., 1978) and Spencer (1998a) collected measurements ofthe short-term activity exposures associated with the use of handheld tools during gasket formation.Spencer took one peak activity sample during his 8-hr study of the use of a ball peen hammer,scribe and hand shears to form gaskets (Table 2) (Spencer, 1998a). The Navy collected several mea-surements of exposures during the use of ballpeen hammers (termed hand punching) with andwithout housekeeping procedures and during the combined use of knives, scissors, and scribes(termed hand shaping). The reported short-term data ranged from <0.03 to 0.15 f/cc (Table 2).Accounting for the average airborne concentration and the number of samples collected for eachstudy, the overall average short-term result associated with the use of handheld tools was estimatedto be 0.10 f/cc for sample durations of approximately 30 min (Table 2).
Several studies, both simulation and work site, measured the 8-h TWA associated with the useof hand-held tools during gasket formation activities. These studies included those of Mangold(2006) (n=4), Spencer (1998a) (n=10), Boelter et al. (2002) (n=4), and Cheng and McDermott(1991) (n=1), and included the use of hand punches, circular cutters, scribes, knives, ballpeenhammers, and shears. These studies reported average 8-h TWA fiber concentrations in the range of0.004 to 0.045 f/cc (Table 2). The studies of Boelter and Spencer and 3 of the studies by Mangold(2006) reported forming 8 gaskets over the course of the 8-h sampling period (Spencer, 1998a,1998b; Boelter et al., 2002; Mangold et al., 2006). The other studies did not report the frequencywith which the task was repeated. The average weighted 8-h exposure associated with the use ofhandheld tools was estimated to be 0.012 f/cc (Table 2).
Cutting of gaskets from rolled asbestos sheets using workshop tools Two work-site studies, thoseby the Navy (Liukonen et al., 1978) and Cheng and McDermott (1991), evaluated exposures asso-ciated with forming gaskets using workshop tools, such as power shears, punches, and nibblers.These work-site studies reported average short-term airborne fiber concentrations during the use ofthese workshop tools ranging from <0.05 to 4.0 f/cc (Table 3). The Cheng and McDermott (1991)samples (n=4) were collected for less than 60 min, and the Navy (n=47) samples were taken for35 min or less (Table 3). The Fowler study (2000), in which stock asbestos gasket sheets were cutinto squares using a band saw, reported airborne concentrations ranging from 2.2 to 4.9 f/cc duringthe use of a band saw (n=4; Table 3). The average weighted short-term concentration of airbornefibers during the use of workshop tools for gasket formation (including the use of a band saw) frommeasurements reported by these studies was estimated to be 0.44 f/cc.
Cheng and McDermott (1991) performed the only study that reported an 8-h TWA for theformation of asbestos gaskets using workshop tools. The authors reported average concentrationsranging from 0.001 to 0.017 f/cc for samples (n=6) collected over 330 to 470 min (Table 3). Chengand McDermott (1991) did not report the number of gaskets formed over the course of the day.The average 8-h concentration of airborne fibers from measurements reported by the authors was0.008 f/cc.
The data from the use of workshop tools are not as consistent as the data from the use of hand-held tools. The Fowler study (2000) clearly showed that using a bandsaw to cut gasket material is atask that can produce excessive airborne concentrations if proper engineering controls are notused; however, this is not a standard or efficient method of cutting gasket materials. None of thestudies described the background concentrations or reported the number of gaskets formed.Despite the uncertainties in the level of activity of the workers, the 8-h TWA measurements of air-borne fibers from the Cheng and McDermott (1991) indicate that these activities do not create high8-h TWA exposures when performed intermittently throughout the day. However, short-term expo-sures (depending on the duration of the sampling) may be relatively high compared to the currentOSHA excursion limit (1 f/cc), and a worker who spends a full shift creating asbestos gaskets in aworkshop without respiratory protection or proper engineering controls might well be exposed toairborne asbestos in excess of the current 8-h PEL. The concentration of asbestos in the gasketmaterial and the vigorousness of the mechanical interaction with the gasket will dictate the airbornefiber concentrations.
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280 A. K. MADL ET AL.
The implications from the available information is that historically, the airborne concentrationsassociated with the use of workshop tools in the formation of gaskets were not in excess of contem-poraneous OSHA standards. Exposure data reported in the studies discussed earlier, excludingthose involving band saw or machine punching without use of basic controls, did not exceed thefirst OSHA PEL (1971) of 12 f/cc, or the PEL of 5 f/cc promulgated in 1972, or the 2 f/cc PEL estab-lished in 1976 (OSHA, 1994a). After 1986, when the 8-h TWA PEL was lowered to 0.2 f/cc, the air-borne concentrations associated with these activities could in some workplaces have been in excessof the PEL if proper controls were not used and if the gasket material was primarily asbestos. Simi-larly, the data indicate that airborne concentrations should not have been in excess of the 15-min10 f/cc ceiling limit until it was lowered to the 30-min 1 f/cc excursion limit in 1988. However, bythe mid-1980s, most industries were using substitute materials for asbestos gaskets or had imple-mented controls to protect workers.
Gasket Removal and Installation Tables 4 and 5 present data from studies on the installationand removal of gaskets, including studies of flange face cleaning using scrapers, wire brushes, andpower wire brushes. The data are categorized by activity and duration of sampling time.
Gasket removal using hand scrapers and wire brushes Six studies evaluated exposures associ-ated with the removal of residual gasket material using manual techniques, specifically hand scrap-ers and wire brushes. The Navy study (Liukonen et al., 1978) characterized airborne fiberconcentrations associated with manual gasket removal and flange cleaning techniques and reportedan average concentration of 0.12 f/cc (n=22) for samples collected for 15 to 35 min (calculated byauthors; Table 4). The Navy also characterized airborne fiber concentrations during hand scrapingafter the gasket had already been removed (n=4), and reported that all of the concentrations wereless than the detection limit of 0.05 f/cc (30 min; Table 4). The worksite study by Cheng andMcDermott (1991) observed higher results for similar gasket removal activities (n=3), with an aver-age airborne fiber concentration of 0.21 f/cc, and data ranging from 0.11 to 0.33 f/cc (less than 1 h;average calculated by authors; Table 4). McKinnery and Moore (1992) reported a geometric meanof 0.16 f/cc (32 min) for manual gasket removal activities (n=23; Table 4) involving tools of thetrade and other tools normally available to maintenance personnel, which likely included thestandard use of scrapers and wire brushes (McKinnery & Moore, 1992). Unfortunately, none ofthese studies on short-term exposures associated with gasket removal activities measured back-ground concentrations prior to the work taking place. Based on the average airborne fiber concen-trations and the number of samples collected in each study, the average weighted short-term fiberconcentration during gasket removal using hand scrapers or wire brushes was likely no greater than0.14 f/cc.
Short-term sampling results during the removal of adhered gaskets from industrial flanges usingmanual techniques were higher than results observed in three work-site studies involving gasketremoval from automobile engine and exhaust parts (Table 7). In the Liukonen and Weir (2005)study, various gasket removal and cleaning methods were used, including hand scraping with achisel and razor and power-wire brushing and puffing. During these activities, 13 of 14 personalsamples (11–60 min) showed results that were ranging from less than the limit of detection, with thelimit of detection (LOD) for these activities ranging from <0.023 to <0.12 f/cc (Liukonen & Weir,2005). Also, removal of automobile exhaust gaskets with minimal flange cleaning (including timerequired for exhaust pipe disassembly) showed average airborne asbestos concentrations of 0.022 f/cc(Paustenbach et al., 2006). In this study, residual gasket was removed by hand or scraped off with ascrewdriver and generally took less than 1 min (Paustenbach et al., 2005). In a third study of auto-mobile engine repair and gasket replacement, gaskets were removed from engine manifolds fromthree vehicles using a putty knife and then a power wire brush after solvent application (Blake et al.2006). Replacement of asbestos-containing gaskets resulted in worker exposures to airborne fiberconcentrations (as measured by PCM) ranging from 0.0032 to 0.027 t/cc (n = 10, 60–156 min)(Blake et al. 2006). Although slightly higher than the airborne fiber concentrations reported forautomobile gasket work, Boelter and Spencer (2003) measured airborne asbestos during theremoval and installation of asbestos-containing gaskets on various engine parts of a Caterpillardozer, grader and loader. Using a variety of tools (i.e., die grinder, chisel, scraper, knife, ball peen
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281
TABL
E 7.
Repo
rted
Sho
rt-Te
rm T
ime-
Wei
ghte
d A
vera
ge (
TWA
) A
irbor
ne F
iber
Con
cent
ratio
ns E
ncou
nter
ed b
y W
orke
rs d
urin
g th
e Re
plac
emen
t of
Asb
esto
s-C
onta
inin
g A
utom
obile
and
Hea
vy E
quip
men
t Gas
kets
Brea
thin
g zo
ne fi
ber c
once
ntra
tion
(f/cc
)
PCM
Stud
yG
aske
ts
Rem
oved
(N)
Site
of G
aske
ts/M
etho
dA
sbes
tos
cont
ent (
%)a
Aver
ageb
Rang
eSD
NBa
ckgr
ound
co
nc. (
f/cc)
App
rox.
sam
ple
dura
tion
(min
)
Gas
ket F
orm
atio
nYe
ung
et a
l.N
RW
orks
hop/
Han
d-he
ld s
aw
and
stam
ping
mac
hine
NR
<0.
05<
0.05
—2
—10
0
Gas
ket R
emov
alPa
uste
nbac
h et
al.
27A
utom
obile
exh
aust
sys
tem
/ Sc
rew
driv
er9.
5–67
0.02
20.
006–
0.06
6—
230.
008
9–65
Blak
e et
al.c
6A
utom
obile
eng
ine/
Put
ty
knife
, pow
er w
ire b
rush
w
ith s
olve
nt
14–7
00.
013
<0.
01–0
.027
—6
0.00
05–0
.001
560
–141
Liuk
onen
& W
eir
48A
utom
obile
eng
ine
and
exha
ust m
anifo
ldN
D-7
0<
0.03
50.
017–
<0.
120
—14
NR
35–1
03
Ove
rall
Ave
rage
0.02
0G
aske
t Ins
talla
tion
Blak
e et
al.c
NR
Aut
omob
ile e
ngin
e/(p
resu
mab
ly p
refo
rmed
) ga
sket
s gl
ued
to fl
ange
su
rface
and
reas
sem
bled
NR
0.00
40.
0032
–0.0
058
—4
0.00
05–0
.001
515
1–15
6
Gas
ket r
emov
al a
nd
inst
alla
tion
Boel
ter &
Spe
ncer
d22
Hea
vy c
onst
ruct
ion
equi
pmen
t (D
ozer
, Gra
der,
Load
er)/D
ie g
rinde
r, ch
isel,
scra
per,
knife
, bal
l pee
n ha
mm
er
3–85
0.09
0.04
4–0.
46—
420.
017
30
Not
es. N
, num
ber o
f sam
ples
; PC
M, p
hase
con
trast
mic
rosc
opy;
TEM
, tra
nsm
issio
n el
ectro
n m
icro
scop
y; N
O, n
ot d
etec
ted;
NR,
not
repo
rted
; SD
, sta
ndar
d de
viat
ion;
f/cc
, fib
ers
per c
ubic
cent
imet
er; T
WA
, Tim
e W
eigh
ted
Aver
age;
—, n
ot a
pplic
able
. In
stud
ies
that
did
not
repo
rt m
ean
conc
entr
atio
n or
sta
ndar
d de
viat
ion,
thes
e va
lues
wer
e ca
lcul
ated
from
ava
ilabl
e da
ta u
sing
one
half
the
limit
of d
etec
tion
for
calc
ulat
ions
invo
lvin
g sa
mpl
es b
elow
the
limit
of d
etec
tion.
Any
val
ues
that
are
not
rep
orte
d as
arit
hmet
ic m
eans
or
stan
dard
dev
iatio
ns a
re n
oted
app
ropr
i-at
ely.
a All
asbe
stos
-con
tain
ing
gask
ets
cont
aine
d ch
ryso
tile
asbe
stos
onl
y.b Av
erag
e co
ncen
tratio
n re
pres
ents
the
activ
ity T
WA
for t
he p
erfo
rmed
task
.c Ba
ckgr
ound
con
cent
ratio
n re
porte
d as
a 8
-hr T
WA
.d Ba
ckgr
ound
sam
ples
ana
lyze
d by
TEM
indi
cate
no
dete
ctio
n of
asb
esto
s fib
ers.
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282 A. K. MADL ET AL.
hammer; to remove and install the gaskets, an average airborne fiber concentration of 0.09 f/cc wasobserved with individual measurements ranging from 0.044–0.46 f/cc.
Studies reporting 8-h TWAs for airborne fiber associated with manual removal of industrial gas-kets yielded consistent results. Both Mangold et al. (2006) and Boelter et al. (2002) studied theremoval of 4 to 8 gaskets over the 8-h workday. Boelter et al. (2002) reported an average 8-h TWAof 0.014 f/cc, with data ranging from 0.000 to 0.035 f/cc, for scraping and wire brush activitiesinvolved with the removal of gaskets (n=8; Table 4). Mangold et al. (2006) reported a similar averageconcentration of 0.026 f/cc, with data ranging from <0.005 to 0.07 f/cc for the same activities(n=32; average calculated by authors; Table 4) (Mangold et al., 2006).
Gasket removal using power wire brushes Power wire brushing is much like manual wirebrushing, except that the wire brush is mounted on the end of a power drill or an air-operated tool.The power wire brush is effective at removing those portions of a gasket that remain on the flangeafter the majority has been removed by a knife or scraper, but it is not the preferred method forflange face cleaning. For example, the heat produced by the action of the wire brush can melt thenonasbestos binding material within the gasket, making the face more difficult to clean. In somecases, the power wire brush can score or gouge the flange face. Power wire brushing has not beenstudied as extensively as other gasket removal techniques, in part because it was practiced less fre-quently than the other approaches.
In their work-site study, Cheng and McDermott (1991) reported a value of 1.4 f/cc for one sam-ple collected over 25 min during use of a power wire brush (Table 5) (Cheng & McDermott, 1991).Both Mangold et al. (2006) (n=1) and Boelter et al. (2002) (n=4) performed day-long studies inwhich eight flanges were power wire brushed. Both studies reported results within the range of0.008 to 0.023 f/cc (Table 5). The average weighted 8-h concentration of airborne fiber duringpower wire brushing over a typical workday was estimated to be 0.014 f/cc from these studies(by the authors).
It is intuitive that the mechanical and circular action of the power wire brush would createhigher concentrations of airborne fibers than those observed with manual wire brushing of asbestosgaskets. Based on the time needed to open up a flange, and the preference for scrapers and manualwire brushes during flange face cleaning, it is unlikely that the power wire brush would be usedmore than eight times in one day or for more than a few minutes at any time. Based on our experi-ence, power brushing rarely occurred. Even so, the studies mentioned indicate that the 8-h expo-sures during power wire brushing should have been well below the current OSHA 8-h TWA PEL.However, the data reported by Cheng and McDermott (1991) for short-term exposures indicatethat this activity could have produced airborne concentrations for a few minutes that are in excessof the current OSHA 30-min excursion limit.
Wet gasket removal Two studies, both conducted at work sites, characterized exposures dur-ing the removal of wet gaskets (Cheng & McDermott, 1991; Spence & Rocchi, 1996). The purposeof wetting gaskets is to keep fibers from becoming airborne. The gaskets are wet with water or someother type of solvent that may assist in loosening the gasket. Cheng and McDermott (1991) reportedthat both air samples (n=2) associated with this activity were below the limit of detection (0.06 f/cc;Table 5) (Cheng & McDermott, 1991). Spence and Rocchi (1996) reported samples (n=21) rangingfrom below the limit of detection to 0.242 f/cc by PCM analysis (Table 5), although the TEM analy-sis of the same samples indicated that fiber concentrations were equal to or less than 0.0037 f/cc.This led Spence and Rocchi (1996) to conclude that PCM analysis was mostly counting the fiber-glass insulation that was removed from the pipes. Overall, the data presented in the two work-sitestudies show an average concentration of 0.03 f/cc for short-term samples collected over the dura-tion of the activity and 0.085 f/cc for an 8-h exposure, and demonstrate that exposures to airbornefibers during wet gasket removal are minimal.
Installation of gaskets Four studies, those by Mangold et al. (2006), Spencer (1998b), the Navy(Liukonen et al., 1978), and McKinnery and Moore (1992), evaluated exposures associated with theinstallation of gaskets. The Navy collected four samples for 30 min during gasket installation (with-out housekeeping procedures or ventilation), all of which were below the limit of detection of 0.03f/cc (Table 5) (Liukonen et al., 1978). The Navy also collected 28 samples during the removal and
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installation of gaskets with housekeeping (and without any flange face cleaning), and reported anaverage concentration of 0.09 f/cc for samples ranging from 0.02 to 0.3 f/cc taken over 20 to 95min (Table 5). Spencer collected one 30-min sample during his simulation study on the installationand removal of gaskets (no flange face cleaning) and reported that the concentration was less than0.045 f/cc (Table 5) (Spencer, 1998a).
McKinnery and Moore (1992) reported results with a geometric mean of 0.2 f/cc for gasketinstallation activities lasting an average of 31 min (n=12; Table 5). Based on the results presentedin these studies, gasket installation including and excluding gasket removal and flange face cleaningdid not exceed an average concentration of 0.20 f/cc for short-term (activity only) samples and0.008 f/cc for long-term (8-h) samples. In addition, the average weighted short-term concentrationof airborne fibers during gasket installation only (without gasket removal or flange cleaning) was esti-mated to be 0.154 f/cc.
Simulation studies conducted by Mangold et al. (n=4) and Spencer (n=2) reported similarresults for workday exposures during installation of gaskets, with the 8-h breathing zone measure-ments being at or below 0.015 f/cc (Table 5) (Spencer, 1998b; Mangold et al., 2006).
Packing Removal and Installation Table 6 presents data from studies on packing removaland installation. Some of the studies performed these tasks separately, while others sampled duringthe combined activities. The data are categorized by activity sampled and duration of sampling.
Packing removal and installation studies Two simulation studies, one by McKinnery andMoore (1992) and the other by Millette and Mount (1993), measured average short-term exposuresassociated with dry valve packing removal and/or replacement activities. The McKinnery andMoore (1992) study reported a geometric mean concentration of 0.29 f/cc for samples (n=21) col-lected from the worker’s breathing zone during packing removal activities (lasting approximately 46min) and 0.10 f/cc for samples (n=18) collected during packing installation activities (lastingapproximately 26 min; Table 6). The study by Millette and Mount (1993) reported an average fiberconcentration of 0.72 f/cc (n=5) for packing removal activities conducted over 30 min (calculatedby authors). Exposures associated with the installation of valve packing were not evaluated in thisstudy. Combining the results from these studies, the overall weighted-average short-term concentra-tion was estimated to be 0.37 f/cc for packing removal and 0.10 f/cc for installation activities.
Three simulation studies, by Spencer (1998b), Mangold et al. (2006), and Boelter et al. (2002),examined airborne fiber exposures associated with the removal and installation of valve packing on4 to 8 valves over the course of an 8-h day. The overall 8-h average airborne fiber concentration forthese studies was estimated to be 0.014 f/cc with measurements ranging from 0.008 to 0.027 f/cc(n=9; Table 6), concentrations well below the current OSHA 8-h TWA PEL of 0.1 f/cc and all pre-vious exposure limits (Spencer, 1998a; Boelter et al., 2002; Mangold et al., 2006).
CONCLUSIONS
The differences among the studies presented in this analysis, such as sampling times, samplingand analytical methods, and activities characterized, made it difficult, at times, to directly comparethe results of each study. It would have been helpful if the original researchers had presented adetailed account of the methods they used so that proper inferences from the data could be made.The studies that did not characterize background concentrations could be considered a worst-casescenario at best, and if more studies on this topic had been available, these poorly documentedstudies would probably not have been considered in this review. In addition, many of these studiesdid not report the time taken to perform an activity or the number of times an activity wasrepeated, making it difficult to estimate a typical 8-h TWA for persons who routinely replaced gas-kets. Acknowledging the problems and limitations of these studies, it is possible to gain insight intothe likely short- and long-term airborne fiber concentrations associated with installing and removingasbestos gaskets and packing.
Our assessment of the published and unpublished literature on airborne fiber concentrationsduring gasket and packing replacement shows that (1) gasket formation resulted in average short-termand 8-h TWA concentrations of 0.44 and 0.008 f/cc, respectively, when workshop tools were used,
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(2) gasket formation using hand-held manual tools produced short-term concentrations near 0.1 f/ccwhile the 8-h TWA concentrations were about 0.01 f/cc, (3) gasket removal and flange face cleaningwith hand tools averaged 0.14 f/cc for peak concentrations and 0.024 f/cc during the 8-h workday,(4) gasket installation (no removal or cleaning) averaged about 0.15 f/cc for short-term concentra-tions, and (5) packing removal and installation showed an average airborne concentration of about0.40 f/cc or less during peak exposures but averaged about 0.01 f/cc over the 8-h workday.
The purpose of this analysis was to assemble all the available information so that one can esti-mate, with some level of confidence, the concentration of airborne fibers attributable to workingwith asbestos packing and gaskets that occurred during the years when asbestos was used in thesematerials. The data used were collected by PCM analysis, which measures the fibers regulated byOSHA, but does not count all respirable asbestos fibers. However, even if such data were available,they would not be directly comparable to the OSHA exposure limits or to the majority of the datacollected over the past several decades that were used in setting the regulatory levels. Althoughasbestos was a major component in gaskets and packing materials for well over 50 yr in the UnitedStates, the weight of evidence from the various studies discussed here indicates that installing andremoving these materials should not have posed a significant health hazard. The only activity that inmany cases may have generated airborne concentrations in the breathing zone of workers in thevicinity of or above the current OSHA excursion limit of 1 f/cc is the removal of residual gasketmaterial from flanges using a powered wire brush. Because mechanical removal has been reportedto occur infrequently and because the activity took usually less than 1–2 min when it did occur, the8-h TWA airborne concentrations for most persons performing this task would have been beloweven the current PEL of 0.1 f/cc.
The data presented in this analysis indicate that workers who were routinely involved in makingasbestos sheet gaskets in the field, or those who installed and removed asbestos packing and gasketmaterials, for the period 1940–1985, should not have been exposed to 8-h TWA airborne concen-trations of chrysotile asbestos in excess of the OSHA PELs promulgated prior to 1986.
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