Laserfiche WebLink
ASBESTOS and OTHER FIBERS by PCM:METHOD 7400,Issue 2,dated 15 August 1994-Page 14 of 15 <br /> These rules are sometimes referred to as the W rules: <br /> Object Count Discussion <br /> 1 1 fiber Optically observable asbestos fibers are actually bundles of fine fibrils.If the <br /> fibrils seem to be from the same bundle,the object is counted as a single <br /> fiber.Note,however,that all objects meeting length and aspect ratio criteria <br /> are counted whether or not they appear to be asbestos. <br /> 2 2 fibers If fibers meeting the length and aspect ratio criteria(length>5 µm and <br /> length-to-width ratio>3 to 1)overlap,but do not seem to be part of the <br /> same bundle,they are counted as separate fibers. <br /> 3 1 fiber Although the object has a relatively large diameter(>3 µm),it is counted as fi- <br /> ber under the rules.There is no upper limit on the fiber diameter in the count- <br /> ing rules.Note that fiber width is measured at the widest compact section of <br /> the object. <br /> 4 1 fiber Although long fine fibrils may extend from the body of a fiber,these fibrils are <br /> considered part of the fiber if they seem to have originally been part of the <br /> bundle. <br /> 5 Do not count If the object is s 5 µm long,it is not counted. <br /> 6 1 fiber A fiber partially obscured by a particle is counted as one fiber.If the fiber ends <br /> emanating from a particle do not seem to be from the same fiber and each <br /> end meets the length and aspect ratio criteria,they are counted as separate <br /> fibers. <br /> 7 1/2 fiber A fiber which crosses into the graticule area one time is counted as fiber. <br /> 8 Do not count Ignore fibers that cross the graticulate boundary more than once. <br /> 9 Do not count Ignore fibers that lie outside the graticule boundary. <br /> APPENDIX C.ALTERNATE COUNTING RULES FOR NON-ASBESTOS FIBERS <br /> Other counting rules may be more appropriate for measurement of specific non-asbestos fiber types, <br /> such as fibrous glass.These include the"B"rules given below(from NIOSH Method 7400, Revision#2, <br /> dated 8/15/87),the World Health Organization reference method for man-made mineral fiber[241,and <br /> the NIOSH fibrous glass criteria document method [251.The upper diameter limit in these methods <br /> prevents measurements of non-thoracic fibers.It is important to note that the aspect ratio limits <br /> included in these methods vary.NIOSH recommends the use of the 3:1 aspect ratio in counting fibers. <br /> It is emphasized that hybridization of different sets of counting rules is not permitted.Report <br /> specifically which set of counting rules are used with the analytical results. <br /> "B"Counting Rules <br /> 1. Count only ends of fibers.Each fiber must be longer than 5 µm and less than 3 µm diameter. <br /> 2. Count only ends of fibers with a length-to-width ratio equal to or greater than 5:1. <br /> 3. Count each fiber end which falls within the graticule area as one end,provided that the fiber meets <br /> rules 1 and 2 above.Add split ends to the count as appropriate if the split fiber segment also meets <br /> the criteria of rules 1 and 2 above. <br /> 4. Count visibly free ends which meet rules 1 and 2 above when the fiber appears to be attached to <br /> another particle,regardless of the size of the other particle.Count the end of a fiber obscured by <br /> another particle if the particle covering the fiber end is less than 3 µm in diameter. <br /> NIOSH Manual of Analytical Methods(NMAM),Fourth Edition <br />