Exposure to asbestos fibres during gasket removal

Our plain-English summary of Exposure to asbestos fibres during gasket removal, by S.K. Spence, P.S. Rocchi (The Annals of Occupational Hygiene, 1996).

The study

• Authors: S.K. Spence, P.S. Rocchi
• Journal: The Annals of Occupational Hygiene
• Published: 1996;40(5):583-8
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In the chemical industry, asbestos gaskets have been used extensively to prevent leakage between solid surfaces. The purpose of this study was to assess the potential personal exposure to asbestos fibres during gasket removal and thus to determine what is reasonably required in terms of protective regime and work method. Two groups were studied: group A, who only removed gaskets if they could be removed easily and without breaking; and group B, who removed gaskets which were left by the first group. For both groups, the gasket was first made wet before removal. The samples were analysed using phase-contrast microscopy and transmission electron microscopy. The average exposure to fibres for group A, averaged over the work period, was 0.04-0.242 fibres ml-1 as determined by phase-contrast microscopy. On further analysis with transmission electron microscopy it was found that only four of the 11 samples contained asbestos in very low concentrations and that most of the fibres, which were identified using phase-contrast microscopy, probably originated from the glass fibre lagging around the pipes. For group B the average fibre concentration, averaged over the work period, as determined by phase-contrast microscopy, ranged between below the detection limit and 0.02 fibres ml-1. The subsequent transmission electron microscopy analysis shows that the exposure to asbestos fibres ranged between below the limit of detection to 0.004 fibres ml-1. This study shows that the exposure to asbestos fibres during gasket removal activities was well within the 8-h average exposure limit of 0.3 fibres ml-1.

In plain English

The authors measured personal airborne fibre levels for maintenance workers removing gaskets during real chemical-industry work. The article describes both gasket types studied as made with chrysotile asbestos (spelled "crysotile"), though not every gasket removed contained asbestos. Group A wore disposable half masks, wetted gaskets and removed only those that came out easily. All of group A's gaskets were spiral wound, and only five contained asbestos. Group B, a trained team in full protective gear, removed the harder asbestos plate gaskets left behind. Using phase-contrast microscopy (PCM), group A's average fibre levels were 0.042 to 0.242 fibres per ml. Electron microscopy (TEM) found asbestos, at very low levels, in only four of 11 samples. The authors said most of the fibres probably came from pipe insulation. Group B's PCM levels ranged from below the detection limit to 0.02 fibres per ml, and the only TEM asbestos result above detection was 0.0037 fibres per ml. The authors concluded that exposures were well within the 8-hour limit of 0.3 fibres per ml and that a wetting agent gave adequate protection. They also concluded that PCM overestimated asbestos where other fibres were present.

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: Workplace personal air-monitoring study during real gasket removal work (not a simulation), with filters analysed by both phase-contrast microscopy and transmission electron microscopy
• Who was studied: Maintenance workers removing gaskets in the chemical industry, in two groups. Group A (11 samples) removed only easily removable gaskets. Group B, a trained team working in the evening, removed the gaskets group A left. The study was carried out under Dutch asbestos legislation.
• Exposure: Removal of spiral wound gaskets (described as chrysotile filler between stainless steel windings) and plate gaskets (described as compressed chrysotile sheets bound with nitryl or neoprene). Gaskets were wetted before removal. Group A wore a P3 disposable half mask. Group B used P3 power pack respirators, isolation of the area and full decontamination. Not every gasket removed by group A contained asbestos.
• Main results:
  • Group A (all spiral wound gaskets): average total fibre concentration by PCM was 0.042 to 0.242 fibres per ml
  • Group A: averaged over 8 hours, PCM exposure was 0.036 to 0.215 fibres per ml
  • Group A: TEM found asbestos, in very low concentrations, in only four of the 11 samples
  • Group A: on bulk analysis, only five of the gaskets removed contained asbestos
  • Group A: the authors said the fibres counted by PCM probably came from piping insulation removed before the gaskets
  • Group B (all asbestos plate gaskets): average fibre concentration by PCM ranged from below the detection limit to 0.02 fibres per ml
  • Group B: converted to an 8-hour average, PCM values ranged from below the detection limit to 0.005 fibres per ml
  • Group B: the only TEM asbestos result above the detection limit was 0.0037 asbestos fibres per ml
  • PCM overestimated the asbestos fibre concentration in this study
• The authors' conclusion: The authors concluded that asbestos exposures during gasket removal were well within the 8-hour average exposure limit of 0.3 fibres per ml. They concluded that a suitable wetting agent gives adequate protection while avoiding unnecessary control measures. They also concluded that PCM may not be applicable where mixed fibres are present.
• Limitations the authors state:
  • Because the study used a real work situation, few of the gaskets removed by group A actually contained asbestos
  • There was no way to know in advance whether group A would encounter asbestos gaskets or substitutes

Topics

Medical terms in this study, explained in our Lexicon: Gasket, Transmission Electron Microscopy (TEM).

Related studies

• Fiber release during the removal of asbestos-containing gaskets: a work practice simulation — W.E. Longo, W.B. Egeland, et al. (2002)
• An exposure study of bystanders and workers during the installation and removal of asbestos gaskets and packing — C. Mangold, K. Clark, et al. (2006)
• Exposure to airborne asbestos during removal and installation of gaskets and packings: a review of published and unpublished studies — A.K. Madl, K. Clark, et al. (2007)
• The removal of fibres of chrysotile asbestos from lung — A. Morgan (1994)
• Effect of respiratory protective equipment on exposure to asbestos fibres during removal of asbestos insulation — H. Akkersdijk, C.F. Bremmer, et al. (1989)
• Assessment of airborne asbestos exposure during the servicing and handling of automobile asbestos-containing gaskets — C.L. Blake, G.S. Dotson, et al. (2006)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.