Document mbjoy0OjdGZea7VkBX8vY9b8J

INTERNAL CORRESPONDENCE UNION CARBIDE CORPORATION 270 PARK AVENUE, NEW YORK, NEW YORK 10017 To (Nome! DiWiion location Mr. John A. Riddle Chemicals & Plastics P. o. Box K King City, California 93930 oat, January 19, 1968 Originating Dopi. Me d i C a 1 Antwtring l,tf,r dal. Copy to Svb/ocf Dear John: The relation between crociaolite and mesothelioma seems to be pretty strongly established by experience in South Africa and elsewhere. The relation between chrysotile and mesothelioma is not clear. If it exists, it apparently is much less prounced than that shown by crocidolite. The limit of 5 MPPCF that we observe in our operations is still recognized in the United States as satisfactory for chryso tile, but there is strong feeling that it is much too high for crocidolite. I wouldn't be at all surprised to see supplied-air respirators recommended for handling the latter. In our own operations with chrysotile, I feel that we should try to control the dust to levels as far below 5 MPPCF as reason ably possible. That is, I don't believe we should be content with control that just maintains the level at 5 MPPCF. Actually, this figure is known as a threshold guide and not a level that strictly defines safe and unsafe conditions. There is some thought that metals associated with asbestos either from the ore or from milling machines, etc., may be part of the problem. Investigation is underway to evaluate this potential; and as soon as I hear more about it. I'll let you know. PWMrdmf DISTRIBUTION J. A. Riddle L. F. Crew R. O. MarwEn Q W. E.Ktvcapple Q A. A. Andrade Q G. C. Brice Q Snifters Q J. 1. Myers K. A. Wood S. Kamens Q G- tassels K. West File n Very truly yours, Paul W. McDaniel Industrial Hygiene Engineer A 1 791Q RECEIVED jan 22 19GB U.C.C. CHEM. & PLASTICS ........ ~ < IP. '<OR.r.l4B:2 UNION CARBIDE INTERNAL CORRESPONDENCE CHEMICALS AND PLASTICS To(Hamt) OhUn Paul W. McDaniel Ath Floor NYC Copfto P/^t)t. BOX K, KING CITY, CALIFORNIA 93s>30 oaM January 11, 1968 OrigtaaSag DapL Aamrbg ItHtr daf* **6fJ Dear Paul: Enclosed Is a copy of an article from the San Francisco Chronicle re mesothelioma and asbestos. I would be Interested In your reaction. Is 5 MMPCF still considered good enough, or should we go to remote-controlled equipment and alr-llne masks like the nuclear Industry uses? I've seen one article which implies that crocldollte may be the harmful variety rather than chrysotlle. Have you anything on comparative toxicology of various species of asbestos? Very truly yours, J. A. Riddle JAR/jcb Enc: A