Fiber counting

Fiber counting A microscopic technique which is of particular relevance to asbestos, where the fibers are counted on a filter paper. 

Air drawn through a 0.8 to 1.2 mm cellulose ester membrane filter, asbestos fibers counted by positive phase contrast microscopy technique sample prepared by acetone/triacetin method (NIOSH Method 7400, 1985). 

Counting all fibers is an approach that gives greater protection to employees. However, economic and enforcement considerations may require that proof of the kind of fibers counted be made In those circumstances where there is reasonable cause to believe other fibers are present as an interference, it is desirable to know how "other information" can be obtained. 

When asbestos is in a mixture with other fibers, it is possible to bracket the asbestos concentration by determining the percent of asbestos fibers in the mixture removed from the membrane and applying this percentage to the total fiber count on the membrane. 

NIOSH has collaboratively tested the fiber counting procedure and has observed a statistical counting error no greater than 20%. 

Figure 8. Number of fibers counted in the camera s focal plane 2.5 cm below the furnace centerline after a number of standard growth experiments where the hydrogen jacket pressure was held constant at the values shown. Bottom curve refers to a series of 304 tubes. In the top curve 304 tubes which had previously grown fibers and whose surfaces were treated with Fe(NO ) were used.

Churg A. 1982. Fiber counting and analysis in the diagnosis of asbestos-related disease. Hum Pathol 13(4) 381-392. 

Results of a survey of asbestos fibers in consumer cosmetic talc powders from Italian and international markets using electron microscopy, electron diffraction, and energy dispersive x-ray analysis showed that asbestos was detected in 6 of 14 talc samples from the European Pharmacopeia (Paoletti et al. 1984). Chrysotile was identified in 3 samples, 2 samples contained tremolite asbestos and anthophyllite asbestos, and 1 sample contained chrysotile and tremolite asbestos. The authors noted that, in all talc powders analyzed, fibrous talc particles frequently were present that were morphologically similar to amphibole asbestos fibers. Counting fibers as particles with aspect ratio >3 1 and width < 3 m, the percentages of particles that were asbestos fibers ranged from <0.03% to 0.13% for 4 samples, and were 18% to 22% for the other 2 samples. Paoletti et al. (1984) noted that the European Pharmacopeia, at that time, had not established analytical quality control of asbestos contamination. 

Accurate fiber counts were carried out using both scanning electron microscopy (SEM), and high magnification phase light microscopy. 

Creatine Increases androgen receptor site counts and supplies greater ATP for improved recovery. Additionally, research suggests creatine is beneficial in cholesterol management and positively influence muscle fiber counts. Aids in post-cycle lean mass retention. 

The second factor was obtained by mounting radioactive fibers, counting them, dissolving them with a concentrated HNO3 solution, and drying and counting the disk on which the fiber was dissolved. The second factor is the ratio of the second count to the first. An average of 11 determinations was... 

Birrfelder, P., Dorrestijn, M., Roth, C., Rossi, R.M., 2013. Effect of fiber count and knit structure on intra- and inter-yam transport of liquid water. Text. Res. J. 83, 1477-1488. 

Fiber counting Airborne fiber concentrations determined using OM refer strictly to those fibers that are longer than 5 pm, have diameters less than 3 pm, and have an aspect ratio of less than 3 1. The aspect ratio may be slightly different in some countries. All the... 

There is no independent method available to determine the accuracy of fiber counts, although mass... 

If it is assumed that both the deposition of fibers on the filter and the selection of fields for counting are random, then there will be a variability in the results that can be described by a Poisson distribution. For fiber counts of 50 this leads to 95% confidence intervals in the results of + 15 (30%) and a coefficient of variation of 15%, although for smaller fiber counts the variability will be much larger. In addition to this variability there is an unavoidable degree of nonuniformity of the asbestos deposit on the filter. There is also subjective variation between microscopists in interpretation of fiber structures and in their ability to detect and identify fibers. Overall counting performances caimot then be expected to produce a coefficient of variation better than 25% for counts of 50 fibers. 

Good quality control procedures are essential to keep these subjective variations to acceptably low levels, and satisfactory performance in both internal and external fiber counting exchange schemes is usually recommended by regulatory authorities. 

The analytical sensitivity of fiber counting methods is usually accepted as being a single fiber found in the course of a standard search. With conventional methods, this may translate to airborne fiber concentrations of 0.1 fiber per liter in ambient samples of 1 m, or 1000 fibers per liter for water samples of 11. 

The detection limits are determined by the number of fibers in suitably prepared blank filters and by the random nature of the filter and of the search. In some electron microscopy preparations, where no fibers are found in the blank controls, the detection limit has been taken as 3.69 times the sensitivity (the upper 95% confidence limit for zero in a Poisson distribution). Otherwise, as in PCOM, where a nonzero blank control is common, a higher detection limit prevails. Thus a series of blank filters might produce an average fiber count of five fibers in a standard analysis, which for routine air samples ( 0.5m ) could translate into a detection limit of 0.01 fibers per milliliter. 

Fiber count The number of warp fiber/yarn (ends) and filling fiber/yarn (picks) per inch. Cross section or thickness of fiber, yarn or roving expressed as denier. See Fiber decitex. 

Composite Fabrication. Orthotropic composites were fabricated using the PP/VB (50/50 wt.%) woven preforms. Four fabric preform layers were placed between layers of polypropylene sheet as shown in Figure 2. In order to produce orthotropic composites, the fabric layers were alternately oriented 90° because the woven preforms possessed different fiber counts in the warp and weft directions. The composites were consolidated at 200°C and 3500 kPa using a model 2696 Carver Laboratory Press with heated plates. The thickness of the PP sheets used in the composite fabrication process was varied in order to achieve the desired final composite composition and to control the distribution of the four fabric layers across the composite cross section. 

Fiber counts shall be made by positive phase contrast using a microscope with an 8 to 10 X eyepiece and a 40 to 45 X objective for a total magnification of approximately 400 X and a numerical aperture of 0.65 to 0.75. The microscope shall also be fitted with a green or blue filter. 

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