Journal of Toxicology and Environmental Health, Part B, 10:259–286, 2007 Copyright © Taylor & Francis Group, LLC ISSN: 1093-7404 print / 1521-6950 online DOI: 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EXPOSURE TO AIRBORNE ASBESTOS DURING REMOVAL AND INSTALLATION OF GASKETS AND PACKINGS: A REVIEW OF PUBLISHED AND UNPUBLISHED STUDIES Amy K. Madl, Katherine Clark, Dennis J. Paustenbach ChemRisk, Inc., San Francisco, California, USA In recent years, questions have been raised about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 exposed to asbestos-containing gaskets and packing materials used in pipes, valves, and machinery (pumps, autos, etc.). Up until 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 with encapsulated 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 on valves or pipes used in the study). Specific activities evaluated included the removal and installation of gaskets and packings, flange cleaning, and gasket formation. In all but one of the studies relating to the replacement of gaskets and packing using hand-held tools, the short-term average exposures were less than the current 30-min OSHA excursion limit of 1 fiber per cubic centimeter (f/cc) and all of the long-term average exposures were less than the Downloaded By: [LaBoon, John] At: 14:18 17 July 2007 current 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 performed by pipefitters or other tradesmen in nearly all plausible situations would not have produced airborne concentrations in excess of contemporaneous regulatory levels. Gaskets and packing materials are used in every industry that makes use of pipes, pumps, and valves. 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 easily manipulated, 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. The asbestos fibers in gaskets were primarily incorporated with rubber, styrene-butadiene rubber, or neoprene 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 those found 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 packing due 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 throughout industrial and maritime operations, refineries, chemical plants, naval ships, and energy plants (Lindell, 1972; Cheng & McDermott, 1991; Millette et al., 1996; Spence & Rocchi, 1996). Naval specifications 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 the removal and installation of gaskets and packing. Although we initiated this evaluation, financial support for the underlying research was provided by a pump manufacturer involved in asbestos-related litigation regarding gaskets and packing. One or two of the authors has served 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] 259 260 A. K. MADL ET AL. 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 to a 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 and installation 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 assessment of 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 continued into the 1980s. The extensive use of asbestos insulation on pipes and machinery up until the late 1960s and early 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 asbestos gaskets and packing materials. That is, the background airborne concentration of asbestos on ships due to insulation often exceeded the contribution that might have been due to handling gaskets and packing. Later studies tried to limit background asbestos levels by simulating the work activity in controlled environments (e.g., laboratory test facilities). It was not until 1991 that the first study of this 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 be safely handled if appropriate procedures were followed. Since then, a number of studies have eval- Downloaded By: [LaBoon, John] At: 14:18 17 July 2007 uated airborne fiber exposures during these activities, and some of these have raised concern about the 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 the daily (4 to 8 h) airborne fiber concentrations. This review, to the best of our knowledge, is the first to 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 packing materials. 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 standard work practices of handling encapsulated asbestos gaskets and packing materials. Each study was evaluated 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 or packing), (2) the types of tools used to manipulate the asbestos-containing materials, (3) whether work 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 for different 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 or encapsulated in a binding material (Selikoff, 1970; Lindell, 1972). In 1972, the International Agency 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 ASBESTOS-CONTAINING GASKETS AND PACKINGS 261 gasket materials