Page 223 - Advanced Mine Ventilation

Respirable Dust Sampling and Measurement 203

Table 12.4 The Variation of Quartz Percentages Between Laboratories
in the 1980 NIOSH PAT Program

Method Range of Variation
Overall 33.7%e47.4%
Colorimetric 35.4%e48.4%
Infrared 23.6%e44.0%
X-ray 31.2%e39.5%

for the analysis of dust from metal mines owing to interference. MSHA initially chose
the IR method owing to its capability to detect quartz in very small sample sizes as
found on the personal sampler filter [18].
Apparently, both the IR and X-ray diffraction methods are capable of accurately
determining the percentage of quartz in a dust sample. However, the reported percent-
age error is dependent upon the primary quartz standard used for comparison. The
latter is often a greater source of error. Human errors can also be significant. Since
1975, NIOSH has sponsored a Proficiency Analytical Testing (PAT) program to
monitor the performance of various analytical laboratories. The NIOSH 1980 study
[19] is summarized in Table 12.4. A total of 61 laboratories were surveyed; 28 labo-
ratories used the X-ray diffraction, 21 laboratories used the calorimetric method, and
12 laboratories used the IR method.
NIOSH sent several dust samples to all of the laboratories, and they determined the
percentage of quartz in the dust. NIOSH then determined the percentage variation
(shown in Table 12.4) in the reported results. The large variation between laboratories
emphasizes the need to standardize the analytical methods used to determine the quartz
percentage. The weight of the respirable dust sample must be large enough to avoid
large weighing errors. Different laboratories must use an approved primary quartz
standard. At present, it is not uncommon for a laboratory to produce its own primary
quartz standard. Duplicate analysis or analysis of more than one sample can reduce hu-
man errors considerably.

12.5.3 An Independent Study

The author conducted a survey of many of the working sections in mines, which were
on a reduced dust standard. The purpose of the survey was (1) to identify the sources of
quartz in each mine, (2) to determine the accuracy of MSHA’s sampling, and (3) to
determine the number of samples needed for reliable (true mean 20%) measurement
of quartz concentration in the working place.