Document RpXn0nG9qvLOKK8oK3Z4rME3X

CHEMICALS AND PLASTICS P. O. BOX 9341, SOUTH CHARLESTON, WEST VIRGINIA 25303 U (Nkw) WHUm Uctfton Capy to Mr. R. N. Wheeler South Charleston, Bldg, I<39 Mr. R, L. Anderson, 511 Mr. T. W. Carmody, NYO-31 Mr. R. E. Graehert, 511 Mr. H, R. Gvc.t, 511 Mr, C. D. Hendrix, 511 Mr. A. W. luh., NYO-28 Dr. A. B. Steele, NYO-28 Mr. R. W. Wesson, NYO-32 Mr. J. W. Whittlesey, N-yO-46 Dr. N. L. Zutty, NYO-32 M. . * Dpi. June 3, 1974 Research and Development Proposed Standard for Exposure to Vinyl Chloride Dear Mr. Wheeler: In accordance with your telephone request of May 28, I have reviewed the wording of the proposed permanent OS HA standard for vinyl chloride with respect to the statement of background information quoted below. A, Level of exposure. The proposed standard for employee exposure is set at no detectable level, as determined by a sampling and analytical method capable of detecting vinyl chloride at concentrations of I ppm with an accu racy of I ppm 50 percent. It is the consensus of Messrs. Robert L. Anderson, Charles D. Hendrix and myself that the statement as written above leads to varied interpretations with little chance of resolving the differences in viewpoint. It could be argued that an analyds of 1,5 ppm or less would show compli ance. It could also be argued that an analysis of 0,5 ppm or more would show lack of compliance. There are two main reasons for diverging interpretations. One is that the description of the method to be used Is not precise. The other is that the statement of I ppm 50% refers to the method, not the permissible limit. A permissible limit of "none detectable", is virtually undefinable, evan when coupled with a definition of the method to be used. 'I4 In order fo minimize varying lnterpretation*,the I ppm sensitivity and the reproducibility of the method could be worded as follows: "The proposed standard for employee exposure Is set at no detectable level/ as determined by a method capable of detecting I ppm with a reproducibility (2) of 0.5 ppm at the 95% confidence level (2)/ as defined by ASTM Stan dard E 180-67." The above statement would provide a valid technical basis for a mutual understanding of the requirements of the method to be used. Even with the Improved definition of the method/ It would still be true that for all practical purposes a concentration level of 0.3 ppm or less would be required in order to assure an analysis showing compliance. (At 0.3 ppm the reproducibility of the method would be expected to be about 0.15 ppm). Similarly a concentration of 3.0 ppm or more would be required in order to give an analysis conclusively showing non-compliance. (At 3.0 ppm the re producibility of the method would be expected to be about 1.5 ppm.) These relationships can be illustrated by the attached dtagranv which shows the three zones of reproducibility associated with the use of the specified method X Am-- Nl. H. Ketcham (1) Federal Register, Vol. 39 No. 92, May 10, 1974, page 16896. (2) "Reproducibility" and "Confidence Level" are defined In ASTM Standard E 180-67, Reapproved in 1972. These definitions are in paragraphs A 2.14 and A 2.12, re spectively. Part F of E 180 illustrates the use of these terms In precision statements. NHK/ml Attachments 0018^5 . .1 ; v: ?} - ^7 1 1 Reproducibility of the method when analyzing a known con centration of 3.0 ppm Reproducibility of the method at the "detectable concentra tion " of I ppm Reproducibility of the method when analyzing a known con centration of 0.3 ppm Vj Uo. V,? 5 V * 55 a< O' f 0.45 L< 0.3 0.15 u *% V4 tj 1' 3 50% I 50% 0.3 50% i I | GO18^6