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Asbestos exposure in asbestos insulation removal work at #asbestos2014


Presentation made at the International Conference on Monitoring and Surveillance of Asbestos-Related Diseases 11-13 February 2014, Finland.

Presentation made at the International Conference on Monitoring and Surveillance of Asbestos-Related Diseases 11-13 February 2014, Finland.

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  • We heard on the first day of the conference about the role of the Second World War in promoting the use of asbestos on ships. Around these times there was also increasing use of asbestos in buildings, both for insulation of hot plant such as boilers, pipes etc. It was clear this was totally uncontrolled and immediately at the end of the war the British labour inspectors wrote to those involved in ship building and repair to tell then they must act to control exposure in line with the regulations that applied to asbestos factories.
  • However, little was done and the insulators, whose job it was to remove asbestos, carried out with out much effort to control exposure. During the 60s there was increasing public awareness of the problems with asbestos because of the recognition of the risk for mesothelioma, and in 1970 new regulations were enacted that tightened procedures for removal.
  • In the 1970s the role or asbestos abatement worker, as distinct form insulator, begins. Government codes of practice result in progressive tightening of controls and we see the start of the phenomenon of “enclosure” of the work where removal takes place. By the end of the 1980s we have relatively tight restrictions on work involving asbestos insulation and sprayed coatings.
  • In the 1990s there was renewed focus on trying to reduce the exposure of the worker removing asbestos, in particular the use of wet removal and other controls to minimize the emissions at the actual source. To the present we have further steps that are designed to discourage wholesale removal of asbestos insulation and to focus building owners attention on managing asbestos present in their properties.
  • In parallel with these changes we saw a progressive tightening of the limit values for all types of asbestos. From the 1960s when the measurements were in terms of particles rather than fibres (hence the fuzziness on the graph) to the present situation where we have the same limit for all types of asbestos.
  • As we have seen the measurement methods changed, particularly between the 1970s and early 80s when there were concerted international efforts to get agreement on the methodology. In parallel there was the realization that any analytical method that relies on the subjective human judgment is prone to error and needs to be controlled through stringent quality assurance. In the 1970steh most experienced laboratories in the world differed on average by up to 3x, and other laboratories would have had much greater variability.
  • We have undertaken a systematic search of the literature on exposure during removal. As is generally the case there are really only a small number of papers that are informative and in our case we have ended up extracting data from just 7, plus a small number of key papers of reports that do not show up in computerised searches.
  • The first relevant work comes from the British Navy and the work of Surgeon Commander Harries. In this preliminary report he only gives ranges and no real details of how the samples were collected or over what duration, but these data were sufficient for him to comment that removal or “tearing down” of insulation was a serious problem. The highest quoted concentration is 3800 f/ml in bagging waste.
  • In 1971 Harries published a more extensive set of data. Here he explained more of the methods used. Many samples were taken using small hand pumps with sampling volumes of a few 100 mls, presumably over just a few minutes. The figure shows data for removal activities (AM and range). About 200 samples. The highest levels were obtained from small spaces.
  • These data are for removal of crocidolite from an aircraft carrier, again AM and range. Note that in adjacent areas the levels were about a third to a fifth of the levels in the room where the insulation was being removed. There was no attempt to confine the contamination.
  • Contemporary to the British work measurements were being made in the USA by Balzer and Cooper. The levels are lower than Harries but I wouldn’t put a great deal of store in this because none of these authors fully describe their methods and so much variation can occur because of sampling strategy and methodology that other than to say they are all “high” the exact figures are unclear.
  • We carried out an extensive study of asbestos removal workers in the 1990s that was not published in the peer-reviewed literature but is publically available in report format. Here I’ve summarised the data by categorization of the removal methodology, from Good wet removal using only manual methods etc. Nine sites over several days.
  • Here is data from one site where power tools were used. You can see that…
  • Here are data from the published literature (GM and 5th / 95th percentile or range). There are seven studies that contribute to these. I have subdivided them intro wet or glove bag techniques and dry removal, and you can see…
  • Now lets turn to the effectiveness of respirators. There are even fewer data here and much of it is in the IOM report that I described earlier. These studies rely on measurements made simultaneously inside and outside respirators. It is conventional to express the results as a protection factor, i.e. the multiple by which the exposure is reduced from outside to inside the respirator.
  • So for example, this study by Akkersdijk et al saw average exposure levels reduce from about 25 to about 0.5 f/ml giving a protection factor of 50. However, some of their in-mask measurements were still above the limit value and so the investigated whether improving the fit of the resirator could increase the PF and they got it up to 370.
  • These are the data from our own studies of in mask to ambient level, plotted as a scatter plot; each point representing a pair of measurements. You can see there is no correlation between the measures and so the concept of a PF is meaningless. However, note that although most of the measured ambient levels were above 0.1 f/ml, and in fact many were above 10 f/ml, there were only three in-mask concentration measurements above 0.1 f/ml. This is very reassuring and suggests that these respirators are working extremely effectively.
  • Bystanders are likely to be exposed, and we saw from the data from the aircraft carrier that contamination spreads without containment. We can characterize the workplace into two parts the NF where the worker is located, which is often close to the source, and the FF away from the source where a bystander is located. These data show fro a range of scenarios from MMMF in a small contained room to Asbestos use in a large building the ratio of NF to FF. In large spaces that are well ventilated bystanders are less likely to be exposed than in small confined spaces, such as on ships.
  • Using the NF/FF paradigm it is possible to mathematically model the relationship. So for a single room of say 30 m3 as you increase the ventilation the ratio of NF to FF increases. As you increase the room volume to relation remains the same but the magnitude of the difference between NF and FF increases. The smaller spaces are typical of asbestos enclosures and so everyone inside the enclosure gets much the same exposure, and this exposure is high because the small space essentially enhances the concentration.
  • Of course enclosures are not absolutely sealed and if you measure outside you can normally detect some airborne fibres. These data form Perkins and colleagues show that levels around 0.02 – 0.03 f/ml were not untypical in the past (presumably when the concentration inside the enclosure was around 10 f/ml or more. Note enclosures provide better containment in this study than glove bags.
  • In 1980s in Britain levels up to 0.5 f/ml were measured during clearance testing, although the vast majority of instances were much lower.
  • The evidence suggests that levels trend to 0.005 f/ml although the evidence from this study by Ryan and other work done by Burdett and colleagues from eth HSL shows that there are low levels of asbestos in the air for many months after a removal event.
  • To conclude:


  • 1. Asbestos exposure in asbestos insulation removal work John Cherrie, Andy Stelling, Alan Jones, Geoff Smith INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK
  • 2. Summary • • • What will we cover? Changes over the last 70 years Airborne fibre levels during removal • • • • • • The bad old days Control by wetting and enclosure The impact of using power tools How effective are respirators? Bystanders were exposed Exposure after work complete Photos from
  • 3. Scope of paper… • Include: • • Exclude: • • removal, take out, remediation, disturbance, disrupt, damage, demolition and disposal of insitu asbestos containing materials in buildings, ships and industrial plant or equipment maintenance on gaskets, brakes, ceiling tiles, floor tiles etc Only release into workplace air • Including both workers, bystanders and others
  • 4. The seven ages of removal… <1940s Widespread use of asbestos insulation in buildings and ships 1945 Action taken… British Factory Inspectors express concern about conditions on ships
  • 5. The seven ages of removal… 1950s 1960s 1965 1970s Removal part of the insulators job. No serious attempt to control exposure Awareness of the very high exposure in shipbuilding and elsewhere Sunday Times "Scientists track down killer dust” New regulations in Britain to deal with asbestos in factories etc. Asbestos remediation workers begin work
  • 6. The seven ages of removal… 1970s 1980s Clearance testing begins (using hygiene standards as a benchmark) First Government and industry codes introduced Improved codes of practice for safe work introduced “Work with asbestos insulation and asbestos coating” (1981) Procedures progressively tightened
  • 7. Innovations…
  • 8. The seven ages of removal… 1990s 1992 2000+ Movement towards management in preference to removal Enforcement of wet removal as opposed to dry Close supervision of removal work Duty to manage Consolidation of control limits Removal of action levels as deemed „not safe‟
  • 9. Limit values in Britain…
  • 10. Changes in fibre measurement… • • • • • 1960s particle counting methods to membrane filter method In 1972 IARC recommended that interlaboratory trials be carried out Trials in late 1970s showed average differences between laboratories could be up to 3x Prior to 1980 there was little standardisation and inadequate quality assurance It wasn‟t until the 1980s that measurement Walton, W. et al. (1976). An international comparison of methods H.were harmonizedcounts of airborne asbestos fibres sampled on membrane filters. Ann OccHyg, 19(3-4), 215–224.
  • 11. Published studies • • A systematic review of the literature Search terms • • • • Asbestos, chrysotile, crocidolite, amosite Exposure, air concentration, fibres or fibers/ml, fibres/cc, mppcf Removal, remediation, disturbance, damage Retrieved 741 papers • • • • Screened using title and abstract 16 papers considered potentially informative Data extracted from 7 papers Also included other known informative sources
  • 12. Surgeon Commander Harries… Harries, P. G. (1968). Asbestos hazards in Naval Dockyards. The Annals of Occupational Hygiene, 11(2), 135–145.
  • 13. Pipe lagging on ships… Harries, P. G. (1971). Asbestos dust concentrations in ship repairing: a practical approach to improving asbestos hygiene in naval dockyards. Ann OccupHyg, 14(3), 241–254.
  • 14. Sprayed asbestos removal… Harries, P. G. (1971). Asbestos dust concentrations in ship repairing: a practical approach to improving asbestos hygiene in naval dockyards. Ann OccupHyg, 14(3), 241–254.
  • 15. Balzer and Cooper in the USA Balzer, J. L., and Cooper, W. C. 1968. The work environment of insulating workers. Am. Ind. Hyg. Assoc. J. 29: 222–227.
  • 16. Summary of IOM data… Howie, R. et al (1996). Workplace effectiveness of respiratory protective equipment for asbestos removal work (No. HSE CRR 112:90. ). Report (pp. 1–90). HSE.
  • 17. Use of power tools… Howie, R. et al (1996). Workplace effectiveness of respiratory protective equipment for asbestos removal work (No. HSE CRR 112:90. ). Report (pp. 1–90). HSE.
  • 18. Other data…
  • 19. The effectiveness of respirators • • Sampling simultaneously inside and outside the respirator Results expressed as a Protection Factor (PF)
  • 20. The effectiveness of respirators Akkersdijk, H., et al(1989). Effect of respiratory protective equipment on exposure to asbestos fibres during removal of asbestos insulation. Ann OccHyg, 33(1), 113–116.
  • 21. Workplace protection factors Howie, R. et al (1996). Workplace effectiveness of respiratory protective equipment for asbestos removal work (No. HSE CRR 112:90. ). Report (pp. 1–90). HSE.
  • 22. Workers and bystanders • Exposure of bystanders will be lower than workers • Far-field vs Near-field exposure Cherrie, J. (1999). The effect of room size and general ventilation on the relationship between near and far-field concentrations. App OccupEnvHyg, 14(8), 539–546.
  • 23. Modeling results… Cherrie, J. (1999). The effect of room size and general ventilation on the relationship between near and far-field concentrations. App OccupEnvHyg, 14(8), 539–546.
  • 24. Levels near enclosures… Perkins, J. L., Rose, V. E., & Cleveland, M. S. (1992). Analyses of PCM asbestos air monitoring results for a major abatement project. Applied Occupational and …, 7(1), 27–32.
  • 25. After removal work complete… • • • • • “Clearance test” began in the 1970s 1970s – Used the OELs 1980s – IOM started to use 0.05 fibres/ml as an in-house limit 1983 – Clearance indicator of 0.01f/ml widely adopted (EH10) 1987 – UK hygienists Code of Practice
  • 26. Exposure during clearance tests Bailey, S., Conchie, A., Hiett, D. M., & Thomas, C. (1988). Personal exposure to asbestos dust during clearance certification. Annals of Occupational Hygiene, 32(3), 423–426.
  • 27. Elevated levels post removal… Ryan, G. et al (1996). A longitudinal study of an american public building following asbestos removal. Applied Occupational and Environmental Hygiene, 11(12), 1417–1423.
  • 28. Conclusions • • • • • • Exposure levels were very high with dry stripping and when using power tools Enclosures increase exposure levels Wetting, use of fibresupressants, glove bags and other controls can help reduce levels below 1 fibre/ml If correctly worn respirators probably reduce exposures below 0.1 f/ml Bystanders may have had high exposures Airborne fibre levels remain slightly elevated post removal