Burdett Garry J, Dewberry Kirsty, Staff James
Health and Safety Laboratory, Harpur Hill, Buxton, Derbyshire SK17 9JN, UK
Health and Safety Laboratory, Harpur Hill, Buxton, Derbyshire SK17 9JN, UK.
Ann Occup Hyg. 2016 Jan;60(1):27-39. doi: 10.1093/annhyg/mev062. Epub 2015 Aug 26.
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.
本研究的目的是调查在天花板通风腔或其他空间中含有铁石棉绝缘板（AIB）的学校教室中，可能释放到空气中的石棉浓度，特别是在作为暖空气加热系统一部分存在强制空气再循环的情况下。在三所学校的每所学校的三个或更多教室中采集空气样本，其中两所学校采用CLASP（地方当局特别计划联盟）系统建造设计，样本采集时间为学校无人占用期间。对两种情况进行了采样：（i）加热系统启动并运行且无干扰（背景情况），以及（ii）模拟干扰期间加热系统的运行。模拟干扰的设计强度超过了在有人占用的教室中通常会对AIB产生的干扰水平。在采样期间，对封装或封闭的AIB材料施加了总共60次或更多次使其振动和/或弯曲的直接冲击。冲击在采样开始时进行，并每隔一小时重复一次，但不会破坏或损坏AIB。背景样本的目标空气体积约为3000升，使用放置在加热器出口下方或距离加热器出口约1米处的静态采样器。这将实现每毫升0.0001根纤维（f ml⁻¹）的分析灵敏度（AS），这比欧盟和英国工作场所控制限值0.1 f ml⁻¹低1000倍。还采集了空气体积较小的样本，以防过载以及用于一个地点较短的干扰采样时间。通过相差显微镜（PCM）对采样器过滤器进行分析，以快速确定释放的可见纤维（所有类型）的总体浓度，和/或通过分析透射电子显微镜（TEM）确定石棉纤维的浓度。由于纤维数量较少，结果以计算浓度和统计相关的定量限（LOQ）报告，这是常规应用的。PCM纤维浓度均低于LOQ，但分析TEM显示背景样本中计数的纤维很少是石棉。从所有三所学校分析的单个样本的背景TEM石棉浓度等于或低于AS，合并平均值低于LOQ（<0.00005 f ml⁻¹）。在两所CLASP学校，模拟干扰条件下教室空气中的铁石棉浓度没有显著增加。在第三所学校，在模拟干扰条件下，采样的五个教室中有四个通过TEM测得可测量的铁石棉浓度。PCM可计数的铁石棉纤维最高浓度为0.0043 f ml⁻¹，合并平均值为0.0019 f ml⁻¹。空气采样策略有效且运行良好，结果为学校石棉的采样和管理提供了进一步的重要证据。
