Exposure and risks from wearing asbestos mitts

Our plain-English summary of Exposure and risks from wearing asbestos mitts, by J.W. Cherrie, M. Tindall, H. Cowie (Particle and Fibre Toxicology, 2005).

The study

• Authors: J.W. Cherrie, M. Tindall, H. Cowie
• Journal: Particle and Fibre Toxicology
• Published: 2005;2:5
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Very high fibre inhalation exposure has been measured while people were wearing personal protective equipment manufactured from chrysotile asbestos. However, there is little data that relates specifically to wearing asbestos gloves or mitts, particularly when used in hot environments such as those found in glass manufacturing. The aim of this study was to assess the likely personal exposure to asbestos fibres when asbestos mitts were used.

Results: Three types of work activity were simulated in a small test room with unused mitts and artificially aged mitts. Neither pair of mitts were treated to suppress the dust emission. The measured respirable fibre exposure levels ranged from <0.06 to 0.55 fibres/ml, with no significant difference in fibre exposure between aged and unused mitts. The use of high localised ventilation to simulate convective airflows from a furnace reduced exposure levels by about a factor of five. Differences between tasks were statistically significant, with simulated "rowing" of molten glass lowest and replacement of side seals on the furnace highest. Estimated lifetime cancer risk from 20 years exposure at the upper end of the exposure range measured during the study is less than 22 per 100,000.

Conclusion: People who wore asbestos mitts were likely to have been exposed to relatively low levels of airborne chrysotile asbestos fibres, certainly much lower than the standards that were accepted in the 1960's and 70's. The cancer risks from this type of use are likely to be very low.

In plain English

In this simulation study, the authors measured airborne fibres in the breathing zone of someone wearing chrysotile asbestos mitts. A test subject spent 30 minutes on each of three glass float-bath tasks in a small enclosure: "rowing" molten glass, replacing a window, and replacing a side seal. One pair of 1970s mitts was unused, one artificially aged. Tests ran with and without strong upward ventilation mimicking furnace air currents. Average levels per test condition ranged from 0.03 to 0.48 fibres/ml (33 personal samples). Ventilation significantly lowered levels, and tasks differed significantly. Aged and unused mitts did not differ significantly. The authors modelled risk for one hypothetical glass worker first employed at age 20, using mitts for 20 years, exposed 10 minutes per task daily at the estimated 90th-percentile level (annual average 0.012 fibres/ml). Best-estimate lifetime risks were around 3 per 100,000 for mesothelioma and under 1 per 100,000 for lung cancer. The "highest arguable" estimates were 16 and 6 per 100,000. The authors concluded the cancer risk was low. They said continuous task repetition probably raised measured levels and the small room may have.

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: Laboratory simulation of past work tasks in a test enclosure with fibre measurement, plus a modelled cancer risk estimate using the Hodgson and Darnton method
• Who was studied: A single test subject wearing a respirator, working in an asbestos test enclosure of about 45 cubic metres. Two pairs of chrysotile asbestos gloves made in the 1970s were supplied by a glass company. There were twelve tests, five of them repeated, giving 33 personal samples. The article does not state where or when the tests took place.
• Exposure: Chrysotile asbestos mitts. One pair was unused. The other was artificially aged by heating for 20 hours at 100°C and then hammering. Each mitt was worn for 30 minutes on each of three glass float-bath tasks (rowing molten glass with a steel pole, removing and replacing a window, removing and replacing a side seal). Tasks were done with no ventilation and with high localised upward ventilation of about 3 to 4 m/s.
• Main results:
  • Mean personal fibre concentrations per test condition were 0.03 to 0.35 fibres/ml for rowing, 0.05 to 0.48 fibres/ml for glass window repair, and 0.09 to 0.47 fibres/ml for side seal replacement (33 personal samples in total).
  • High localised ventilation lowered exposure levels, and the decrease was highly statistically significant. The authors estimated that exposures next to a glass float bath were about a fifth of what they would otherwise have been.
  • Differences between the three tasks were highly significant (p less than 0.01). Rowing gave lower concentrations than window repair and side seal replacement.
  • Fibre concentrations did not differ significantly between aged and unused mitts.
  • With high ventilation, results for window repair and rowing were below the analytical detection limit. Side seal replacement gave 0.09 to 0.14 fibres/ml.
  • The risk model assumed a glass worker first employed at age 20 (in 1955) who used chrysotile mitts for 20 years. He was assumed to be exposed for 10 minutes at the estimated 90th percentile level for each task each day, giving an annual average exposure of 0.012 fibres/ml.
  • For this hypothetical worker, the best estimate of lifetime mesothelioma risk was around 3 in 100,000, and lung cancer risk was less than one per 100,000.
  • Under the 'highest arguable' risk assumptions for the same hypothetical worker, the estimates were 16 per 100,000 for mesothelioma and 6 per 100,000 for lung cancer.
• The authors' conclusion: The authors concluded that wearing asbestos mitts would have given relatively low cumulative exposures to chrysotile asbestos. Allowing for uncertainties, they concluded that the risk of death from cancer must be low, which they believed to be trivially low.
• Limitations the authors state:
  • Each task was repeated continuously (about 100 times in 30 minutes), unlike intermittent real work. The authors said this probably produced higher concentrations than real workplace use.
  • The small test enclosure may have increased exposures compared with the larger real work area.
  • The experiments did not account for exposure from residual asbestos contamination in a workplace released from damaged clothing.
  • The artificial ageing of the mitts may have been ineffective, which may explain why aged and unused mitts gave similar results.
  • The real upward convective airflow next to a hot glass tank could not be measured, so the ventilation level used was an assumption.
  • The risk estimates are uncertain. This is because of how exposure was estimated, the exposure-risk analysis used, and the need to extrapolate to low exposures.
  • The lung cancer estimates reflect past smoking prevalence among older British men. Non-smokers would have substantially lower predicted risks, and lifetime smokers would have about double the quoted lung cancer risks.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile.

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