Document KRMg4GaVBQ4zYOz3danxz9vLK
UC 148-2 f
INTERNAL CORRESPONDENCE
UNION CARBIDE CORPORATION
RECEIVED JUN 2 5 1969
V/m.c. rn'M. & rustics
270 PARK AVENUE, NEW YORK, NEW YORK 10017
To (Name) Division Location
Copy fo
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Mr. J. A. Riddle Chemicals & FlasCics Box K
King City, Calif.. 93930
Originating Dept. Answoring loiter date
Dr. J. J. Welsh/Dr. K. S. Lane Sobfad
June 20, 1969 Medical Department
Dear Mr. Riddle: During my recent visit to King City 1 collected samples
DISTRIBUTION
J-. A. Riddle J. L. V/ers-
R. O. Marsten *] R. O. Hopper L. F. Cion 1 r?n-<fe>
RJ. Kronkhyte B. E. Usrey R. Grogan J.M. Andersen A.A. Andraoe K. A. Weed G. L. Vessels.. K. West File l..'
of airborne dust for count with our microscope in New York in
addition to samples we collected for counting with the microscope
at the plant. In both instances the counts were made of particles
greater than 5 microns in length or diameter by phase microscopy at
a magnification of 400 times in accord with the most recent proposed
procedures. The recommended threshold limit for asbestos by this
technique is 12 fibers 5 microns or greater in length per milliliter
of air. As a matter of safety we assumed any particle having a
dimension of 5 microns or more was fiber.
The results we obtained by count with plant equipment
and those obtained by count with the equipment in New York were
as follows:
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Mr. J. A. Riddle
-3- June 20, 1969
As you will note, only at the bagger and on the front end loader moving ore did the count exceed 12 per ml. The bagger operator, of course and all personnel on the dry side of the circuit wear respirators. The operator of the front end loader should also wear a respirator during the type of operation we examined.
During this visit, as you know, we also worked with your laboratory technician (Gabe) in setting up a sampling-counting pro cedure he can follow for monthly surveys of the plant. In August, if possible. I'll again review the procedure with him and evaluate the effectiveness of our techniques.
You may be interested to learn that on Wednesday of this week, at a meeting dealing with asbestos, I briefly discussed the significance of material shorter than 5 microns with Lewis Cralley who is head of the Occupational Research Facility of the U. S. Public Health Service. He told me that they regard the shorter fibers as of significance too, but that they don't know if they are as important as the longer fibers. I intend to visit him in Cincinnati at a later date to further discuss the subject. He emphasized that they have no doubt that asbestos can be handled safely, with practical precautions.
Very truly yours,
PWM: dp
Paul W. McDaniel Industrial Hygiene Engineer
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