(i) Sis Size and count only free fibres which are unattached and have both ends visible. When counting a field, adjust the fine focus control so that any fibres embedded in the filter matrix are not missed. i Count at least one unexposed blank filter treated in the same manner as the set of samples except that no air is drawn through it, in order to obtain the background fibre loading ‘or the 1 samples. The fibre counts for each sample are recorded on an. appropriate form. CALCULATIONS 4 Standard Sample Volumes Use equation to determine the sample volume corrected to standard conditions when necessary: vV=Vv = *- 0.39 K (Vv @) s a sreft a cos — mm Hg aT T a ref a where: v.. sample volume corrected to reference conditions, ml. a - sample volume measured during sampling, ml. - absolute temperature at reference conditions, ref 760 mm Hg. qT. - absolute temperature during sampling, ORY P - absolute pressure at reference conditions, ref 760 mm Hg. P - absolute pressure during sampling, mm Hg. Concentration of Asbestos Fibres Use the following equation to determine the concentration of asbestos fibres in the sample: ss emp mri ge prt aot