Document NGYZz8qgLv3ZeeNbLJ6q0gK0D

\ - 50 Due lo the low absolute quantity and - from a analytical point of view even worse * the extremely low relative quantity of asbestos compared with other inorganic solid substances generally found in samples, it is of little wonder that there i6 still insufficient knowledge about the general occur rence of asbestos in the ambient environment. In the following paragraphs a summary is given of pertinent work on this subject. It has to be kept in mind that results of different investiga tors even if reported in the same units, are often difficult to compare (sec Chapter JV) . * 1. Mr 1.1. in In the U.K. a survey has been made in buildings of different age where the principle types of asbestos-based buildings materials have been used (Byron* ct al, 1969). More than 60 buildings of various types were included in the survey. Sampling and assessment were carried out along guidelines which wore described by Holmes (sec Chapter 3V). The basic method is air fil tration using membrane filters of suitable pore si ?.c (8 pm or lower). The filters are examined using phase-contrast light microscopy enlargement 500 x. Fibres with a diameter <3 pn are taken into consideration only.(sec Chapter v). The results of the survey are summarised in the Tables 1 and ?. from Table 1 we ran deduce - though with reservations - that asbestos is emitted in decreasing quantities in the series: insulation beard, sprayed as bestos, asbestos cement sheeting, other asbestos containing products. run.-:ori r.jng the results of numerous mcAs*.*'t?'.ents carried out in subway stations and public buildings with exposed tprayeibsi^nFuiotior.s containing or.hostof;, concentrations of 10 fibres pur 1C00 cm? w,y:c 'ound using the light microscopic techniques which are used in occupational hyafene. They represent a weight conccr.tration of the order of r.'.f-.gr.i t.udo of 10 ^n/m* which is low, but considerably higher than the asbo:tos concent rutiens found in the open air (Wag (Bit Tab! e< fil > >J >? >3 >A >f OVA? PRODUCED BY FORD