BS ISO 10312-1995
周围环境空气.石棉纤维的测定.直接传递透射电子显微法

Ambient air. Determination of asbestos fibres. Direct-transfer transmission electron microscopy method

标准号

BS ISO 10312-1995

发布日期

1995年10月15日

实施日期

1995年10月15日

废止日期

无

中国标准分类号

C51

国际标准分类号

13.040.20

发布单位

英国标准学会

被代替标准

92/50316 DC-1992

适用范围

1 Substance determined This International Standard specifies a reference method using transmission electron microscopy for the determination of the concentration of asbestos structures in ambient atmospheres and includes measurement of the lengths, widths and aspect ratios of the asbestos structures. The method allows deter-mination of the type(s) of asbestos fibres present. The method cannot discriminate between individual fibres of the asbestos and non-asbestos analogues of the same amphibole mineral. 2 Type of sample The method is defined for polycarbonate capillary-pore filters or cellulose ester (either mixed esters of cellu-lose or cellulose nitrate) filters through which a known volume of air has been drawn. The method is suitable for determination of asbestos in both exterior and building atmospheres. 3 Measuring range The range of concentration which can be determined is 50 structures/mm to 7 000 structures/mm on the filter. The air concentrations represented by these values are a function of the volume of air sampled. There is no lower limit to the dimensions of asbestos fibres which can be detected. In practice, microscopists vary in their ability to detect very small asbestos fibres. Therefore, a minimum length of 0,5 μm has been defined as the shortest fibre to be incorporated in the reported results. 4 Limit of detection The limit of detection theoretically can be lowered in-definitely by filtration of progressively larger volumes of air and by extending the examination of the speci-mens in the electron microscope. In practice, the lowest achievable limit of detection for a particular area of TEM specimen examined is controlled by the total suspended particulate concentration. For total suspended particulate concentrations of ap-proximately 10μg/m, corresponding to clean, rural atmospheres, and assuming filtration of 4 000 litres of air, an analytical sensitivity of 0,5 structure/I can be obtained, equivalent to a limit of detection of 1,8 structure/I, if an area of 0,195 mm of the TEM specimens is examined. If higher total suspended particulate concentrations are present, the volume of air filtered must be reduced in order to maintain an acceptable particulate loading on the filter, leading to a proportionate increase in the analytical sensitivity. Where this is the case, lower limits of detection can be achieved by increasing the area of the TEM speci-mens that is examined. In order to achieve lower limits of detection for fibres and bundles longer than 5 μm, and for PCM equivalent fibres, lower magni-fications are specified which permit more rapid ex-amination of larger areas of the TEM specimens when the examination is limited to these dimensions of fi-bre. The direct analytical method cannot be used if the general particulate loading of the sample collection filter exceeds approximately 10 μg/cm of filter sur-face, which corresponds to approximately 10 % cov-erage of the collection filter by particulate. If the total suspended particulate is largely organic material, the limit of detection can be lowered significantly by using an indirect preparation method.