EPA air monitoring chain of custody, Jan 2003

NYC 9/11 Public Portal Document

ASBESTOS and OTHER FIBERS by PCM: METHOD 7400, Issue 2, dated 15 August 1994 - Page 8 of 15

NOTE: Fiber counts above 1300 fibers/mm and fiber counts from samples with >50% of filter area covered with particulate should be reported as "uncountable" or "probably biased." Other fiber counts outside the 100-1300 fiber/mm range should be reported as having "greater than optimal variability" and as being "probably biased."

21. Calculate and report the concentration, C (fibers/cc), of fibers In the air volume sampled, V (L), using the effective collection area of the filter, A (approx. 385 mm for a 25-mm filter):

V ■ 103

NOTE: Periodically check and adjust the value of A c. if necessary. 22. Report intralaboratory and interlaboratory relative standard deviations (from Step 11) with each set of results. NOTE: Precision depends on the total number of fibers counted [1,16]. Relative standard deviation is documented in references [1,15-17] for fiber counts up to 100 fibers in 100 graticule fields. Comparability of interlaboratory results is discussed below. As a first approximation, use 213% above and 49% below the count as the upper and lower confidence limits for fiber counts greater than 20 (Fig. 1).

EVALUATION OF METHOD:

A. This method is a revision of P&CAM 239 [10]. A summary of the revisions is as follows: 1. Sampling: The change from a 37-mm to a 25-mm filter improves sensitivity for similar air volumes. The change in flow rates allows for 2-m ® full-shift samples to be taken, providing that the filter is not overloaded with non-fibrous particulates. The collection efficiency of the sampler is not a function of flow rate in the range 0.5 to 16 L/min [10]. 2. Sample Preparation Technique: The acetone vapor-triacetin preparation technique is a faster, more permanent mounting technique than the dimethyl phthalate/diethyl oxalate method of P&CAM 239 [2,4,10]. The aluminum "hot block" technique minimizes the amount of acetone needed to prepare each sample. 3. Measurement: a. The Walton-Beckett graticule standardizes the area observed [14,18,19]. b. The HSE/NPL test slide standardizes microscope optics for sensitivity to fiber diameter [4,14]. c. Because of past inaccuracies associated with low fiber counts, the minimum recommended loading has been increased to 100 fibers/mm filter area (a total of 78.5 fibers counted in 100 fields, each with field area = .00785 mm 2.) Lower levels generally result in an overestimate of the fiber count when compared to results in the recommended analytical range [20]. The recommended loadings should yield intracounter S , in the range of 0.10 to 0.17(21,22,23].

B. Interlaboratory comparability: An international collaborative study involved 16 laboratories using prepared slides from the asbestos cement, milling, mining, textile, and friction material industries [9]. The relative standard deviations (Sr) varied with sample type and laboratory. The ranges were:

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94

NYC-WTC_000149412