scope:

General

This International Standard specifies the determination of the number concentration of airbore inorganic fires method in workplace atmosoheres, as defined by the counting criteria given in 4.3.4.

Limitations of the method

The method is applicable for routine sampling and sample evaluation necessary to assess personal exposure to fibres and to control their presence in occupational environments. This method can not identify the composition or characteristics of particular fibre types and its use shall be restricted to workplace atmospheres where the predominant fibre types are inorganic.

The use of this method also has limitations when applied to samples containing platy or acicular particles and consequently it should not be implemented without a full understanding of the workplace atmosphere. There are a variety of analytical methods which can be used to develop a full understanding of complex samples, e.g. polarizing light microscopy, electron microscopy.

With the parameters specified in this method, the theoretical lower detection limit for an 8 h-sample is 0,02 fibres/cm3. However, the limit of practical use is often 0,l fibres/cm3 or higher. This is because blank filters can frequently give a reading of several countable fibres per 100 graticule areas. These "fibres" are contaminants on the filter, or artifacts from the clearing process which have the appearance of fibres. Neither counting more fields nor increasing sampling duration overcomes the problem of background dust, when fibres are a minor constituent of the dust cloud.

The mounting medium proposed in this method has a refractive index of approximately 1,45. In workplace atmospheres where fibres with the refractive indices in the range of I,4 to I,5 may occur, the acetonetriacetine mounting method may not be appropriate and another mounting media shall be used.