Document ZJ42zZRQ5BmD8Z075mNMME9Zp

FILE NAME: AT&T and other Phone Companies (ATT) DATE: 1970 Oct 2 DOC#: ATT038 DOCUMENT DESCRIPTION: Letter Threshold Limit Values for Asbestos and Relevant Air Sampling Techniques - Oases 48086-1 and 48102-1 V-i zi / R. W, STONE, M.D, Medical Direotor - Research Staff AT&TCo - Room 324A 195 Broadway , /"October 2 1970 ') 'i-- --- * ... With reference to the questions raised by Mr. G. W. Hoffman concerning permissible levels of asbestos and relevant air sampling techniques, this is to advise that the official threshold limit values were established by the American Conference of Governmental Industrial Hygienists based on studies by the U. S. Public Health Service. The two air sampling methods in current use are (1) collection on a membrane filter and examination at 430X using phase contrast miscroscopy, and (2) use of the standard impinger collection method and examination by the usual light field techniques. The permissible concentration of fibers by the first tech nique mentioned above is 12 fibers per ml of air, whereas the permissible concentration using the second method mentioned above Is 2 million particles per cubic foot of air. Considering reoent developments in the establishment of causal relationships between air sampling results and the production of positive clinical findings, e.g. mesothelioma, asbestasla, preference is given to the membrane filter tech nique . Collection of air samples and subsequent analysis by phase contrast microscopy should not be attempted by operating company personnel. There are many complexities and subtleties to such techniques} rather, it is recommended that questions about asbestos hazards in operating companies be referred directly to the Bell System Environmental Quality Committee. The Bell System EQC has a ready-made meohanism for handling such questions. .(ORIGINAI SIGNED BY) Mfi~8435~GMW~apw Q* M. VILKBNim OFFICIAL FILE COPY bell T elephone Laboratories in c o r p o r a t e d ATT-CA-PFULB-0020976 SC-PHONE-2125