A risk assessment for exposure to glass wool

Our plain-English summary of A risk assessment for exposure to glass wool, by R. Wilson, A.M. Langer, R.P. Nolan (Regulatory Toxicology and Pharmacology, 1999).

The study

• Authors: R. Wilson, A.M. Langer, R.P. Nolan
• Journal: Regulatory Toxicology and Pharmacology
• Published: 1999;30(2 Pt 1):96-109
• Type of article: Review
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Synthetic vitreous fibers (SVFs) have been widely used as insulation material in places where asbestos was used many years ago and therefore the hazards have been compared. Since the three principal types of asbestos fibers types have caused lung cancer at high exposures, there is a widely held belief that all fibers are carcinogenic if inhaled in large enough doses. Hence, on a morphological basis, SVFs have been studied for their carcinogenic potential. However, there is considerable evidence that differences exist among fibers in their potency to produce a carcinogenic response. In this attempt to carry out a numerical risk assessment for the installers of blown glass wool (fiber) insulation, we start with a characterization of the material; then we review the exposures both in manufacturing and installation. Neither the epidemiological studies of human exposure nor the animal studies have shown a marked hazardous effect from glass wool and we can therefore be sure that any effect that might exist is small. But in this case, as in many other situations where there is a potential hazard, society desires further reassurance and therefore we have made a mechanistic calculation. There are good estimates of the risk associated with exposure to chrysotile asbestos at high exposures and doses. We have therefore taken these numbers and discussed how much less risky an exposure to glass wool fibers might be. We conclude that for a given fiber count, glass wool is five to ten times less risky (and of course the risk might be zero). The risk for a nonsmoking installer of glass wool fiber insulation who wears a respirator is about 6 in a million (and might be zero) per year. This means that out of a million installers there might be six lung cancers from this cause every year or out of 10,000 installers there might be one in 16 years. The low risk of 6 in a million per year of a worker blowing glass wool is consistent with the fact that no one has found any of cancer attributable to the manufacture or installation of glass wool fibers in spite of diligent searches. This is compared with several other occupational risks. Nonetheless common prudence suggests that any installer of blown glass wool fiber insulation wear a respirator.

Copyright 1999 Academic Press.

In plain English

This article was a numerical lung cancer risk assessment for installers of blown glass wool insulation. The authors reviewed published exposure data, human studies and rat inhalation experiments, then scaled chrysotile asbestos lung cancer estimates. They concluded that human studies had not demonstrated an association with respiratory cancer. At those studies' exposure levels, they said, any effect raised normal lung cancer risk by no more than 20%. Some rat groups inhaling synthetic vitreous fibers showed a slight increase in lung cancer, without a pattern. The authors assumed glass wool is five times less potent per fiber than chrysotile. For installers without respirators they assumed an exposure of 1 fiber per cubic centimeter, based on measurements for wool without binder. On that basis they estimated yearly risks of 0.00024 for smokers and 0.000028 for nonsmokers. For nonsmokers using wool without binder and wearing a respirator, the estimate was about 6 in a million per year, possibly zero. The authors said their potency factor cannot be proved or disproved by epidemiology or animal tests. They concluded that regulation was probably inappropriate but that respirators should be a normal precaution.

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: Quantitative (mechanistic) risk assessment that reviewed published exposure data, epidemiological studies and rat inhalation studies, then scaled chrysotile asbestos lung cancer risk estimates to glass wool
• Who was studied: Workers installing blown (loose-fill) glass wool insulation, typically two-person crews blowing insulation into attics. Exposure estimates were drawn from published U.S. measurement studies (Esmen et al. 1982; Lees et al. 1993). No new group of workers was studied.
• Exposure: Airborne glass wool (synthetic vitreous) fibers during installation of blown insulation, with and without binder. For installers without respirators the authors assumed an exposure of 1 fiber/cm3, derived from measurements for blowers of blown glass insulation without binder, adjusted because crews alternate tasks. Chrysotile asbestos was used as the comparison fiber.
• Main results:
  • From their review of human epidemiological studies, the authors concluded that no association between glass fiber exposure and respiratory cancers had been demonstrated.
  • The authors stated that, at the exposure levels of those studies, any effect of glass fiber exposure did not increase normal lung cancer risk by more than 20%.
  • In rat inhalation studies of synthetic vitreous fibers, a slight increase in lung cancer was seen in some exposed rats, without a pattern of increased incidence.
  • From the animal experiments, the authors concluded only that synthetic vitreous fibers are not appreciably worse, fiber for fiber, than chrysotile.
  • Estimated yearly lung cancer risk for installers (blowers) of blown glass wool without binder and without respirators: 0.00024 (2.4 x 10^-4) for smokers and 0.000028 (2.8 x 10^-5) for nonsmokers.
  • For installers of blown wool insulation with binder, the authors estimated that the average exposure, and therefore the risk, would be 14-fold lower.
  • The authors estimated that a respirator reduces risk by a factor of 5 to 10.
  • With a respirator, the estimated yearly risk for a nonsmoking installer of blown glass wool without binder was about 6 in a million (0.000006 in Table 7), and the authors noted it might be zero. Table 7 gives a lower figure for wool with binder.
  • The authors judged that the estimated annual risk for installers, even without special precautions, was not larger than the risks of other occupations.
• The authors' conclusion: The authors concluded that regulation was probably inappropriate, but that good work practices such as wearing an approved respirator should be a normal precaution.
• Limitations the authors state:
  • Exposures to the fibers of concern were not characterized as well as desirable.
  • The assumed factor-of-5 lower potency of glass wool compared with chrysotile cannot be proved or disproved by epidemiology or animal tests.
  • By assuming a linear dose-response relationship, the calculation may produce a risk where in fact there is none.
  • How to compare inhaled doses in rats with doses in glass insulation workers has never been fully resolved.
  • Most of the epidemiological studies reviewed did not separate the effect of cigarette smoking.

Topics

Medical terms in this study, explained in our Lexicon: Vitreous, Lung Cancer, Carcinogenic, Chrysotile, Respirator.

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