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REPORT ON
THE COUNTING OF AIRBORNE ASBESTOS FIBERS
This report presents the results of the project entitled "Counting of Airborne Asbestos Fibers" performed by Clayton I. Environmental Consultants, Inc. (CEC) for the American Petroleum Institute under the terms of an agreement dated September 17, 1974. The project consisted of a one-day workshop of instruction and practice counting at the Clayton Laboratory, the "round robin" counting by 14 participating member companies of API of the asbestos fibers microscope slides prepared and counted by CEC, and the statistical analysis of the results.
The workshop was held at the Clayton Laboratory on April 15, 1975 with representatives of 11 of the 14 companies participating. The first set of prepared slides for the round robin counting was mailed to Participant No. 1 on April 22, 1975. Only 7 participants were able to count this set due to a crystallization of the count ing medium, presumably caused by a combination of delays In mailing and the hot weather of June and July of that year. After due deliberation on ways to circumvent these problems, it was decided to send out a second set of slides during the winter season and request the participants to keep in telephone contact with the Project Director regarding each shipment and receipt of the slides. In addition, it was decided to initiate this series immediately after January 1, 1976 to avoid the risk of loss of the slides in December mailings. Despite these precautions, the second set of slides was lost in the mail after counting had been completed by Participant I'.o. 2. A replicate Set of slides, held in reserve at
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the Clayton Laboratory, wa* men mippea to r*rcica.pnt no. o vlth the further instructions that all future shipments of this set must he made by First Class Mail, Registered, and Return Receipt Requested. With this type of mailing, we were able to complete the round robin testing.
Presentation and Discussion of Results
The Workshop
On April 15, 1975, the workshop was held at the Southfield,
Michigan facility of Clayton Environmental Consultants, Inc. The
following representatives of API member companies participated.
Name
Company
E. R. Averill H. P. Blakeney
R. G. Confer R. M. Curtis A. Fried E. F. Legryk D. F. O'Reilly G. A. Saunders R. L. Stouffer H. M. Taylor R. W. Veit
Mobil Oil Corporation, New York, New York Bayton- Refinery, Exxon Company, U.S.A., Bayton, Texas Exxon Corporation, Linden, New jersey Shell Development Company, Houston, Texas Texaco, Incorporated, Beacon, New York Atlantic Richfield Company,Harvey, Illinois Sun Oil Company, Marcus Hook, Pennsylvania Imperial Oil Ltd., Toronto, Ontario Standard Oil Co. (Indiana), Naperville, Illinois Ethyl Corporation, Baton Rouge, Louisiana Phillips Petroleum Company, Bartlesville, Oklahoma
The participants viewed slides that had been prepared by CEC
end each participant counted the fibers on two of these slides,
The results of these counts are presented in Table I. Slide No. 9
contained chrysotile fibers and Slide No. 11 contained amphibole
fibers. The coefficients of variation for these counts were 0.22
and 0.24, respectively.
To convert fibers per field to an asbestos concentration in
terms of fibers per milliliter of air, it was assumed that the
slides were prepared from air samples collected at 1.7 liters per
minute for 120 minutes. The samples were assumed to have been
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'collected on 37-mm, type aa ***<- = . - - --- -- --r____ ___________
, millimeters In diameter.
Round Robin Counting Tables II and III summarize the results of the round robin
counting conducted during 1975 and 1976, respectively. During 1975 only seven of the participants vere able to complete the counting due to crystallization of the counting medium. The coefficients of variation for the four slides counted during 1975 ranged from 0.24 to 0.84. The fibers on Slides 4 and 7 of this scries vere chrysotile vhile those on Slides 16 and 18 vere amphibole.
During the 1976 series, all participants except Participant No. 9 completed the counting. As shown in Table III, the coefficients of variation ranged from 0.70 to 1.0. For this series, the fibers on Slides 4 and 16 vere amphibole and those on Slides 7 and 18 were chrysotile.
Examination of the data from the two round robin counting series indicated some deterioration in the fiber concentration over time. As a result, the fibers on the four slides used during the 1976 series were recounted at the CEC laboratory after they had been counted by the other participants. The initial count was completed on January 5, 1976 while the second count was done on June 23, 1976, more than five months later. The results of this dual count are displayed in Table IV. As shown, the decrease in fiber concentration ranged from 22 to 82 percent.
As a result of this decrease over time shown in Table IV, an attempt was made to determine a relationship between time and
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fiber concentre cion
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robin counting. However, statistically significant relationship were obtained for only four of the eight data seta. In addition the fora of these significant relationships was'different in
each of the four cases. Thus, it appears that no conclusive atatenent can be made regarding this apparent deterioration in *
fiber concentration over time.
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table I RESULTS OF ASBESTOS FIBER COUNTING DURING WORKSHOP
Participant
CEC 1 2 3 4 5 6 7 8 9
10 11
Mean
Coefficient of
Variation
Asbestos Concentration (Fibers/ml of Air)
Slide No. 9
Slide No. 11
5.31 3.97 2.84 2.84 5.53 4.29 3.94 3.60 4.63 3.11 3.87 3.66
4.61 4.81 3.18 4.08 4.49 5.12 5.39 3.94 5.95 4.15 . 6.57 7.33
3.97
4.97
0.22
0.24
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RESULTS OF 1975 ROUND RODIN ASBESTOS FIB E R COUNTING
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TABLE ZV
RESULTS OF DUAL COUNTING OF 1976 SERIES SLIDES BY
CLAYTON ENVIRONMENTAL CONSULTANTS 1 LABORATORY
Slide No.
4 7 16 18
Asbestos Concentration (Fibers/ml of Air)
Before Round Robin Counting
After Round Robin Counting
7.8 8.4 1.2 0.50
1.4 1.9 0.93 0.26
Decrease (Percent)
82 77 22 48
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