Airborne Asbestos Exposures from Warm Air Heating Systems in Schools

Our plain-English summary of Airborne Asbestos Exposures from Warm Air Heating Systems in Schools, by G.J. Burdett, K. Dewberry, J. Staff (The Annals of Occupational Hygiene, 2016).

The study

• Authors: G.J. Burdett, K. Dewberry, J. Staff
• Journal: The Annals of Occupational Hygiene
• Published: 2016;60(1):27-39
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The aim of this study was to investigate the concentrations of airborne asbestos that can be released into classrooms of schools that have amosite-containing asbestos insulation board (AIB) in the ceiling plenum or other spaces, particularly where there is forced recirculation of air as part of a warm air heating system. Air samples were collected in three or more classrooms at each of three schools, two of which were of CLASP (Consortium of Local Authorities Special Programme) system-built design, during periods when the schools were unoccupied. Two conditions were sampled: (i) the start-up and running of the heating systems with no disturbance (the background) and (ii) running of the heating systems during simulated disturbance. The simulated disturbance was designed to exceed the level of disturbance to the AIB that would routinely take place in an occupied classroom. A total of 60 or more direct impacts that vibrated and/or flexed the encapsulated or enclosed AIB materials were applied over the sampling period. The impacts were carried out at the start of the sampling and repeated at hourly intervals but did not break or damage the AIB. The target air volume for background samples was ~3000 l of air using a static sampler sited either below or ~1 m from the heater outlet. This would allow an analytical sensitivity (AS) of 0.0001 fibres per millilitre (f ml(-1)) to be achieved, which is 1000 times lower than the EU and UK workplace control limit of 0.1 f ml(-1). Samples with lower volumes of air were also collected in case of overloading and for the shorter disturbance sampling times used at one site. The sampler filters were analysed by phase contrast microscopy (PCM) to give a rapid determination of the overall concentration of visible fibres (all types) released and/or by analytical transmission electron microscopy (TEM) to determine the concentration of asbestos fibres. Due to the low number of fibres, results were reported in terms of both the calculated concentration and the statistically relevant limits of quantification (LOQ), which are routinely applied. The PCM fibre concentrations were all below the LOQ but analytical TEM showed that few of the fibres counted in the background samples were asbestos. The background TEM asbestos concentrations for the individual samples analysed from all three schools were at or below the AS, with a pooled average below the LOQ (<0.00005 f ml(-1)). At the two CLASP schools, there was no significant increase in the airborne amosite concentration in the classrooms during simulated disturbance conditions. At the third school, four of the five classrooms sampled gave measurable concentrations of amosite by TEM during simulated disturbance conditions. The highest concentration of amosite fibres countable by PCM was 0.0043 f ml(-1) with a pooled average of 0.0019 f ml(-1). The air sampling strategy was effective and worked well and the results provide further important evidence to inform the sampling and management of asbestos in schools.

© The Author 2015. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

In plain English

This UK study measured airborne asbestos in classrooms of three unoccupied schools with amosite-containing asbestos insulation board (AIB) in ceiling spaces or other areas served by warm air heating systems. Two schools (A and B) were CLASP system-built buildings. The third (C) had AIB in heater cupboards, under-window panels and some ceiling tiles. Air was sampled with the heaters running, first without disturbance and then during simulated disturbance designed to exceed normal classroom activity. Phase contrast microscopy counts of all fibre types were all below the limit of quantification. Electron microscopy, which identifies asbestos, put background asbestos levels in individual samples at or below the lowest level the method could detect at all three schools. Disturbance at the two CLASP schools produced no measurable increase in asbestos fibres of the standard counted size. At School C, disturbance released amosite in four of five classrooms, at up to 0.0043 fibres per millilitre, with a pooled average of 0.0019 for those four. The authors concluded that direct disturbance of the AIB was the only significant source of release. They noted that the schools were sampled without occupants.

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: Field air-sampling study in classrooms. Samples were taken with heaters running under background (no disturbance) conditions and during simulated disturbance designed to exceed normal classroom disturbance. Filters were analysed by phase contrast microscopy (PCM, all fibre types) and analytical transmission electron microscopy (TEM, asbestos identification).
• Who was studied: Three UK schools. School A was a CLASP Mk 5 building of about 1900 m2 and School B a CLASP Mk 2 building of about 2300 m2, both with in-ceiling heaters. School C had AIB around classroom heaters. At least three classrooms were sampled per school. All schools were unoccupied: A and B during a spring holiday, and C 6 weeks after it closed pending refurbishment. The year of sampling is not stated.
• Exposure: Amosite-containing asbestos insulation board (AIB) in ceiling plenums or other spaces where air is recirculated by warm air heating systems. At the CLASP schools the AIB was inside column casings with unsealed tops. At School C it was in heater cupboards, under-window panels and some ceiling tiles.
• Main results:
  • The high-volume samples were designed to detect down to 0.0001 fibres per millilitre, which the authors note is 1000 times lower than the current EU and UK control limit.
  • All PCM fibre concentrations (all fibre types) were below the limit of quantification. TEM showed that few of the fibres counted in background samples were asbestos.
  • Background TEM asbestos concentrations for individual samples from all three schools were at or below the analytical sensitivity (0.0001 fibres per millilitre).
  • School A: TEM of samples taken directly under the vents detected no PCM-equivalent (PCME) asbestos fibres, in either background or disturbance sampling.
  • School A: four short (5 µm or less) asbestos fibres were counted in the disturbance samples: two amosite, one chrysotile and one actinolite.
  • School B: only one asbestos fibre was detected by TEM, a PCME crocidolite fibre in a background sample.
  • At the two CLASP schools, disturbance sampling did not give any measurable increase in PCME asbestos fibre exposure in the classrooms.
  • School C background: only one PCME amosite fibre and one short amosite structure were found.
  • School C disturbance: four of the five classrooms gave PCME amosite fibres above the analytical sensitivity, and two exceeded the limit of quantification. A total of 20 PCME amosite fibres were counted in the five samples.
  • School C disturbance: short-term PCME amosite concentrations reached up to 0.0043 fibres per millilitre. The pooled average was 0.0019 fibres per millilitre for the four classrooms with measurable releases.
• The authors' conclusion: After vigorous disturbance of the accessible AIB panels at School C, the authors concluded that direct disturbance of the AIB was the only significant source of release.
• Limitations the authors state:
  • The schools were sampled without occupants. The authors note that moisture from occupants may influence the airborne release of fibres.
  • The method used to count short amosite structures differed slightly from the published method, which the authors say could cause a small bias in the short-fibre count.
  • The School C disturbance samples were shorter and lower in air volume, so they were less sensitive than the background samples.
  • No PCM results or samples from the side-by-side sampling at School C were released to the authors.
  • The laboratories that did the PCM sampling reported no blank filter counts.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Amosite, Analytical Sensitivity, phase contrast microscopy (PCM), Analytical Transmission Electron Microscopy (ATEM), Air Sampling.

Related studies

• Airborne asbestos in Colorado public schools — D.A. Chadwick, R.M. Buchan, et al. (1985)
• Exposure to Amosite-Containing Ceiling Boards in a Public School in Switzerland: A Case Study — D. Vernez, O. Duperrex, et al. (2019)
• Airborne asbestos levels in school buildings in Italy — A. Campopiano, S. Casciardi, et al. (2004)
• Asbestos contamination in United States schools from use of asbestos surfacing materials — W.J. Nicholson, E.J. Swoszowski, et al. (1979)
• Airborne concentrations of asbestos in 71 school buildings — M. Corn, K. Crump, et al. (1991)
• Indoor air quality differences between urban and rural preschools in Korea — C. Yoon, K. Lee, et al. (2011)

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