Page:NIOSH Manual of Analytical Methods - 7404.pdf/4

 CEL LULO SE INS ULA TIO N: ME TH OD 7404, Issue 1, dated 1 5 Ma rch 2003 - page 4 of 6 NOT E 2:

NOT E 3: NOT E 4:

This m ethod allows for differentiation of fibers based on m orphology. Cellulose fibers are easily distinguished from asbestos and glass fibers by morphology [3]. Do not count any fibers that have parallel sides. Do no t approach c loser than 3 viewing fields from the edg e of the filter. Under certain conditions, electrostatic charge may affect the sampling of fibers. These electrostatic effects are mo st likely to occur when the relative hum idity is low (during dry applicatio n), and when sam pling is perform ed near the source of a erosol. T he res ult is that depo sition of fibers on the filter is reduc ed, espe cially near the edge of the filter. In extre m e ca ses, m uch of the sam ple m ay be a dhe ring to th e ca sse tte itself [4].

CALCULATIONS: 17. Ca lculate and repo rt fiber dens ity on the filter, E (fib/m m 2), by dividing the average fiber count per viewing field, F /n f, minus the m ean field blan k coun t per viewing field, B/n b, by the viewing field area, Af :

18. Calculate and repo rt the concentration, C (fib/mL), of cellulose fibers in the air volume sam pled, V (L), using the effective collection area of the filter, A c (approx. 385 mm 2 for a 25-m m filter):

19. Calculate and report the fiber length ranges( minimum and maximum ) as well as the average length.

EVALUATION OF METHOD: This method draws on both Methods 7400 for counting procedures and 7402 for instrumentation and setup. The m ajor difference is the counting rules have been adapted from the A rules to allow for the cou nting a nd s izing of all cellulose fibers having a 3 :1 or greate r asp ect ra tio and a leng th of at least 5 microns. There are no diameter limits as cellulose fibers are truly 3 dimensional. This is illustrated in the figure s be low. T he c om plex sha pes and con stan tly varying diam eters m ake even a n ap prox imate diam eter d eterm ination impos sible. Sam pling and analysis of both wet and dry cellulose insulation application has shown that there is much more uniform fiber deposition across the filter when the wet process is used. There is also much less fiber lost to the ca sse tte walls.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition