Document 1Yo3KDXrx27a65VXRB3KObaZ

February 8, 1962 THOMAS 0. DONKEY PITTSBURGH ^- MR. F. H. JtEGEHR VBRNON WORKS Ret SAWING MARINITE Reference is made to recent correspondence r the saving of Narinite. We would like to coaasnt on the recoonendation to add additional ventilation to the saw need for catting Merinite. Al though there say be several good reaaosa for ventilating the saw* the decision to ventilate it canaat be nad* on the basis of ito being a health hasard. Aa I understand it, the naterial would be cut at infrequent intervals and probably would not Involve aore than 12 hoars a nonth. the estrese of foar conditions aeasured). We know that Harinite contains asbestos and diatonaceons earth} therefore a threshold Unit of 5 nppcf is a reasonable one to apply. This figure repre sents a tine-weighted average concentration to which nearly all workers can be exposed day after day without adverse effect to the ajorlty of workers* A threshold Hsit tilM of 3 nppcf la aerely a ghlde iittd dust he ttsed'with-a conkJdenrtls^anonnt of Judgnent. However, Marinite dost concentrations nay exceed this value if the daily exposures are less than eight hours. (See the preaable to the ACGXH list of Threshold Values end Pages 2-4 and 2-5 of the Alcoa Industrial Hygiene Handbook). If you have a concentration of 30 nppcf of a non-irritant dust having a threshold Unit of 5 nppcf, it neans that your workers can be exposed daily to the high level for a little over one hoar per day with littlo likelihood of adverse effects. In a nonth, this ARCH 19186 KR.F.H.RBGBHR 2- Peb. 8, 1962 aaaunts to an cllovable exposure of over 40 hours* The actual ex* posure that you have estinated Is 12 hours per aontb, and therefore there is go need for concern about baralng your enployees* This is a conservative estiaate of the situation, especially In view of our using the highest accented concentrations for the evaluation. Granted 30 nppcf i* a rather heavy dust loading and, quite possibly, some ueans of control nay be desirable for other reasons, such as discoafort or nuisance value. If diseoafort and nuisance are the only factors, perhaps slaple respiratory protection would be sufficient* Zt should be roaeabered that the threshold Halt values are ststistlcsl values and that by using theca as intended, we are able to protect the vast majority of the working populatiou* By using TLV*s as intended, flexibly and sensibly, wo can be assured that injury to our enployees is highly unlikely. This assurance is, I think, our aost iaportant objective. Another possible objective is that of being able to disprove alleged injury* Without strict adherence to the TLV*s, this latter end will be difficult to gain, but the problea is likely to be alaest as great even with strict adherence* Although It say not be iaportant in this case, a realistic appraisal of potential hazards and the Judicious use of threshold liait values nay be extrenely iaportant in other instances* Whether or not costly controls arc to be installed nay depend on a careful analysis of each individual problea. TBnjDB cct T.I.McClintock, Vernon H.R.Powell, Vernon W.H.Sharp, Vernon ^r;V.Cralley, flic T.B.Bonney ARCH 19187