Exposure to Airborne Asbestos During Removal and Installation of Gaskets and Packings: A Review of Published and Unpublished Studies

Abstract

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 studies of industrial and maritime settings involving the collection of more than 300 air samples were evaluated to determine 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 representativeness 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 current 8-h permissible exposure limit time-weighted average (PEL-TWA) of 0.1 f/cc. The weight of evidence indicates 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.

Airborne asbestos exposures associated with gasket and packing replacement: A simulation study of flange and valve repair work and an assessment of exposure variables

“…If conducted properly, simulation studies remove the confounding variables of worksite studies and can more precisely represent exposures associated with a particular task and/or product. In general, the data from the simulation studies are consistent with the worksite studies, demonstrating that workers involved in typical work practices in the fabrication of asbestos sheet gaskets and removal and installation of asbestos gaskets and packing materials would not have been exposed to 8-h time-weighted average (TWA) airborne concentrations of chrysotile asbestos in excess of the contemporaneous occupational exposure limits (Madl et al, 2007).…”

Government and Navy knowledge regarding health hazards of asbestos: A state of the science evaluation (1900 to 1970)

“…Over the course of 20-30 years, from about 1970 to 2000, a number of additional studies of worker exposure to so-called "encapsulated materials" were conducted, and these, too, gave the military and others a fair degree of confidence that if handled in a reasonably prudent manner, asbestos containing materials would not pose a significant increased health hazard. Specifically, studies were conducted on floor tiles (Lange, 2006, Lange et al, 2008, gaskets and packing (Cheng & Mcdermott, 1991, Madl et al, 2007, and brakes (Hickish & Knight, 1970, Paustenbach et al, 2004a). After about 1995, in an attempt to answer questions about exposures that likely occurred in the past, but reflected exposures that no longer occurred in the United States, a number of simulation studies or dose-reconstruction studies were conducted to help inform those conducting epidemiology studies or the courts.…”

Occupational exposure to asbestos in the steel industry (1972–2006)

“…From approximately the 1940s through the early 1980s, gaskets, including rope gaskets, and packing materials for valve stems used in the steelmaking industry, if asbestos-containing, contained exclusively chrysotile [ 55 – 58 ].…”