Retrospective exposure assessment of airborne asbestos related to skilled craftsmen at a petroleum refinery in Beaumont, Texas (1940-2006)

Our plain-English summary of Retrospective exposure assessment of airborne asbestos related to skilled craftsmen at a petroleum refinery in Beaumont, Texas (1940-2006), by P. Williams, D. Paustenbach, J.L. Balzer, et al (Journal of Toxicology and Environmental Health. Part a, 2007).

The study

• Authors: P. Williams, D. Paustenbach, J.L. Balzer, C. Mangold
• Journal: Journal of Toxicology and Environmental Health. Part a
• Published: 2007;70(13):1076-107
• Type of article: Historical article
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Despite efforts over the past 50 or more years to estimate airborne dust or fiber concentrations for specific job tasks within different industries, there have been no known attempts to reconstruct historical asbestos exposures for the many types of trades employed in various nonmanufacturing settings. In this paper, 8-h time-weighted average (TWA) asbestos exposures were estimated for 12 different crafts from the 1940s to the present day at a large petroleum refinery in Beaumont, TX. The crafts evaluated were insulators, pipefitters, boilermakers, masons, welders, sheet-metal workers, millwrights, electricians, carpenters, painters, laborers, and maintenance workers. This analysis quantitatively accounts for (1) the historical use of asbestos-containing materials at the refinery, (2) the typical workday of the different crafts and specific opportunities for exposure to asbestos, (3) industrial hygiene asbestos air monitoring data collected at this refinery and similar facilities since the early 1970s, (4) published and unpublished data sets on task-specific dust or fiber concentrations encountered in various industrial settings since the late 1930s, and (5) the evolution of respirator use and other workplace practices that occurred as the hazards of asbestos became better understood over time. Due to limited air monitoring data for most crafts, 8-h TWA fiber concentrations were calculated only for insulators, while all other crafts were estimated to have experienced 8-h TWA fiber concentrations at some fraction of that experienced by insulators. A probabilistic (Monte Carlo) model was used to account for potential variability in the various data sets and the uncertainty in our knowledge of selected input parameters used to estimate exposure. Significant reliance was also placed on our collective professional experiences working in the fields of industrial hygiene, exposure assessment, and process engineering over the last 40 yr. Insulators at this refinery were estimated to have experienced 50th (and 95th) percentile 8-h TWA asbestos exposures (which incorporated 8-h TWA fiber concentrations, respirator use and effectiveness, and time spent working with asbestos-containing materials) of 9 (16) fibers/cc (cubic centimeter) from 1940 to 1950, 8 (13) fibers/cc from 1951 to 1965, 2 (5) fibers/cc from 1966 to 1971, 0.3 (0.5) fibers/cc from 1972 to 1975, and 0.005 (0.02) fibers/cc from 1976 to 1985 (estimated exposures were <0.001 fibers/cc after 1985). Estimated 8-h TWA exposures for all other crafts were at least 50- to 100-fold less than that of insulators, with the exception of laborers, whose estimated 8-h TWA exposures were approximately one-fifth to one-tenth of those of insulators. In spite of the data gaps, the available evidence indicates that our estimates of 8-h TWA asbestos exposures reasonably characterize the typical range of values for these categories of workers over time.

In plain English

This study estimated, rather than measured, past airborne asbestos exposures for 12 crafts at a Beaumont, Texas, petroleum refinery from 1940 to 2006. Using a probabilistic (Monte Carlo) model, the authors combined dust and fiber measurements from published and unpublished studies and from ExxonMobil air sampling with estimated task durations, respirator use and effectiveness, and time spent with asbestos-containing materials. Fiber levels were calculated directly only for insulators. Other crafts were set as fractions of insulator levels using the authors' professional judgment. Insulators' 50th-percentile estimates of 8-hour average exposure fell from 9 fibers/cc (95th percentile 16) in 1940 to 1950 to 0.005 (95th percentile 0.02) in 1976 to 1985, and below 0.001 after 1985. Their 95th-percentile estimate was 0.002 fibers/cc in 1986 to 1993. Laborers' estimates were about one-fifth to one-tenth of insulators'. Masons, maintenance workers, pipefitters, boilermakers, millwrights and carpenters were estimated at least 50 to 100 times lower than insulators. Welders, sheet-metal workers, electricians and painters were at or below 0.01 fibers/cc at the 50th percentile. The authors concluded their estimates reasonably approximate typical exposures. They noted sparse measurement data and uncertainty about which asbestos types were used at the refinery.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective exposure assessment (exposure reconstruction) using a probabilistic Monte Carlo model; no workers' health outcomes were studied
• Who was studied: 12 crafts at a petroleum refinery in Beaumont, Texas, in 7 time periods from 1940 to 2006: insulators, pipefitters, boilermakers, masons, welders, sheet-metal workers, millwrights, electricians, carpenters, painters, laborers and maintenance workers. The estimates apply to crafts and time periods, not to individual workers.
• Exposure: Airborne asbestos as 8-hour time-weighted average fibers/cc. The main source was asbestos-containing calcium silicate and magnesium carbonate insulation that typically contained about 5 to 20% chrysotile, amosite or a blend of the two. Gaskets, packing, blankets and other materials were also considered.
• Main results:
  • Insulators, estimated 8-h TWA asbestos exposure, 50th (95th) percentile: 9 (16) fibers/cc in 1940 to 1950; 8 (13) in 1951 to 1965; 2 (5) in 1966 to 1971; 0.3 (0.5) in 1972 to 1975; 0.005 (0.02) in 1976 to 1985. The 50th percentile was below 0.001 fibers/cc after 1985.
  • Insulators' 95th-percentile estimated 8-h TWA asbestos exposure was 0.002 fibers/cc in 1986 to 1993, and below 0.001 in 1994 to 2006 (Table 11)
  • The estimated decline in insulators' exposures over the 60-year period was more than 1,000-fold
  • Before respirator use and time spent with asbestos materials were accounted for, insulators' estimated 8-h TWA fiber concentration in 1940 to 1950 was 18 fibers/cc. Their estimated exposure for the same period was 9 fibers/cc.
  • Laborers had the second-highest estimates, approximately one-fifth to one-tenth those of insulators
  • Laborers, 50th (95th) percentile, as stated in the text: 1.1 (2) fibers/cc in 1940 to 1950; 0.95 (1.7) in 1951 to 1965; 0.3 (0.7) in 1966 to 1971; 0.05 (0.09) in 1972 to 1975; 0.001 (0.004) in 1976 to 1985; below 0.001 after 1985
  • Masons, maintenance workers, pipefitters, boilermakers, millwrights and carpenters had estimates at least 50 to 100 times less than insulators and about 10 times less than laborers. Their 50th (95th) percentile estimates ranged from 0.02 to 0.14 (0.04 to 0.3) fibers/cc in 1940 to 1950, and were below 0.001 fibers/cc after 1976.
  • Welders, sheet-metal workers, electricians and painters had estimates at or below 0.01 fibers/cc at the 50th percentile and 0.04 fibers/cc at the 95th percentile for all time periods
  • The authors reported that estimates did not exceed the occupational exposure limits in force at the time. Insulators' estimates were about 2 to 6 times below those limits before 1972, assuming a 1:6 conversion factor before 1966. After 1972 they were about 10 to 100 times below.
  • In the sensitivity analysis, the factor used to convert dust counts to fibers accounted for about 70% of the variance in insulators' estimates for 1940 to 1965
  • Using uniform or triangular instead of lognormal distributions changed insulators' estimates by less than two-fold
  • Of 212 insulation bulk samples collected at the refinery in the late 1980s and early 1990s, 96 contained asbestos. Of these, 73 contained chrysotile (76%), 19 amosite (20%) and 4 both.
• The authors' conclusion: The authors concluded that, despite data gaps, their estimates provide a reasonable approximation of the typical range of 8-h TWA asbestos exposures for these categories of workers over time
• Limitations the authors state:
  • Relatively little measured airborne fiber data were available for specific job tasks and time periods, and most of it came from insulators
  • Many insulator data sets came from shipyards, which were of limited value for an outdoor refinery, or were total dust rather than fiber measurements
  • Few task-specific or 8-h TWA samples were collected for the crafts before OSHA was enacted in the early 1970s
  • The authors stated that the historical dust measurements, often taken with imprecise instruments and in shipyards, overestimate the exposures likely at this refinery
  • The asbestos fiber type used over time at the refinery was not known, which limits the ability to predict disease
  • Estimates for crafts other than insulators were less certain

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Time-Weighted Average (TWA), Insulator, Pipefitter, Asbestos-Containing Material (ACM), Industrial Hygiene, Air Sampling, Respirator.

Related studies

• An updated mortality study of workers at a petroleum refinery in Beaumont, Texas — G.K. Raabe, K.W. Collingwood, et al. (1998)
• A review of historical exposures to asbestos among skilled craftsmen (1940-2006) — P.R. Williams, A.D. Phelka, et al. (2007)
• Asbestos-related cancers in refinery workers in the Australian petroleum industry — R. Gun, N.L. Pratt, et al. (2006)
• Long-term follow-up mortality study of petroleum refinery and chemical plant employees — S.P. Tsai, E.L. Gilstrap, et al. (1996)
• Asbestos exposure and cancer mortality among petroleum refinery workers: a Poisson regression analysis of updated data — F. Montanaro, M. Ceppi, et al. (2004)
• Kidney cancer and hydrocarbon exposures among petroleum refinery workers — C. Poole, N.A. Dreyer, et al. (1993)

Browse more research in Journal of Toxicology and Environmental Health. Part a, or return to medical research.