Page 225 - Advances In Productive, Safe, and Responsible Coal Mining

204 Advances in Productive, Safe, and Responsible Coal Mining

11.6.1 Shift average-based monitoring

11.6.1.1 The NIOSH 5040 method
The most accurate method to determine the concentration of DPM in the mine air is
the NIOSH 5040 method. This is an established technique to measure DPM concen-
tration in underground mines. The NIOSH 5040 technique is an analytical method,
which is used to measure EC and OC components of a DPM sample collected on a
quartz fiber filter [54]. The NIOSH 5040 method differentiates carbon content into
organic and elemental components, which makes it more versatile as compared to
the other carbon analytical methods. MSHA considers TC to be the most appropriate
surrogate for DPM as TC contributes over 80% of the particulate matter present in
diesel exhaust [55,56]. Major interferences that are typically found in underground
M/NM mines can affect TC analysis. These interferences are mechanically generated
dust that may contain OC and/or EC, cigarette smoke, oil mist, ammonium nitrate/fuel
vapors from explosive material, and welding fumes [3,32,57]. However, because dust
in M/NM mines generally does not have high carbon content, results of TC and EC
measurements are not significantly influenced by carbon from mineral dust [58]. Size-
selective samplers used during DPM sampling can effectively remove EC and OC
contamination from mineral dust, but these are not effective in removing sub-
micrometer aerosols from cigarette smoke or oil mist [54,59]. Avoiding cigarette
smoke or oil mist is not always possible when taking personal samples and because
these contaminants interfere only with the OC analysis, MSHA proposed using sub-
micrometer EC as a surrogate for DPM [60]. In a typical M/NM mine environment, no
other sources of submicrometer EC are known. Thus, EC can be used as a surrogate for
DPM [60].
The current DPM sampling protocol requires that both personal and area samples
be collected simultaneously over the miner’s full shift [44]. The personal sample is
used to assess personal exposure to TC and EC. One area sample (or sometimes more
than one) is used to assess the relationship between TC and EC. As a part of the alter-
native procedure to determine TC exposure levels, EC concentrations obtained by per-
sonal exposure sampling are multiplied by the ratio of TC to EC obtained from area
sample measurements [32,44]. This EC-based approach to determining TC exposures
is used to minimize the potential for overestimating a miner’s exposures to TC due to
various artifacts that primarily affect the measurement of the OC fraction of TC. The
TC/EC ratio is determined from one or more samples collected in the main exhaust
course of the mine because OC interferences are expected to be negligible in those
samples [32,44].
The NIOSH 5040 method requires four sampling components: a specialized wear-
able pump designed to deliver a constant volume flow with an accurate timing device,
tygon tubing, a 10-mm nylon cyclone, and a DPM filter cassette. Field samples are
collected by a sampling medium that consists of a 37-mm cassette preceded by a
10-mm nylon cyclone. Air is drawn at a flow rate of 1.7l per minute using a calibrated
constant flow sampling pump through the nylon cyclone. The nylon cyclone has a
cutpoint of 4.0μm and an impactor with a cutpoint of 0.8μm at a volume flow rate
of 1.7l per min. These settings serve to physically eliminate most of the mechanically