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Diesel particulate matter: Monitoring and control improves safety and air quality 205

generated mineral dust from diesel aerosol. Before sampling, the cassette and cyclone
assemblies are connected to the calibrated sampling pump by using plastic tubing. Per-
sonal DPM samples are collected by fitting these sampling trains on miners, whereas
area sampling is conducted by installing the monitoring setup at desired locations in
the mine. After the collection of a DPM sample, the cassettes are sealed and sent to a
2
laboratory for analysis. Cassettes are opened and a 1.5-cm rectangular shaped portion
of the filter is removed using a metal punch. This procedure allows three individual
sample analyses for each sample collected [61]. In the laboratory, a thermo-optical
method is utilized to analyze the sample. In the thermal-optical method, separation
of OC and EC is accomplished through temperature and atmospheric control
[62,63]. The NIOSH 5040 method is a direct approach to measure DPM; it can quan-
tify organic and elemental carbon at low (5μg) levels and it is less likely to suffer from
interferences by mineral sources or other combustibles. Thus, it can quantify diesel
particulates in situations where using other shift average methods may not be suitable
[54,61,64].

11.6.2 Real-time monitoring
DPM regulations endorsed in the US by MSHA triggered development of instruments
that can estimate DPM exposure in real time. Generally, these monitors use photo-
acoustic methods or condensation counters to measure respirable combustible dust
and then display an equivalent DPM concentration. Although the NIOSH 5040 is a
standard method used for DPM compliance determination in US M/NM mines, this
method is based on determining shift average concentrations. Thus, it inherently
involves an issue of “lag time” since it requires a postcollection laboratory analysis
for DPM determination. It may take 2 weeks to get laboratory results and miners could
be potentially overexposed to DPM during that time. Like any other shift average-
based measurement method, the NIOSH 5040 method is not suitable to detect rapid
changes in DPM levels, which may occur over the course of monitoring. In order to
determine any change in DPM levels caused by changing mining activities, more than
one mine air sample may have to be collected using the NIOSH 5040 method. This
may increase the amount of work and cost involved in DPM monitoring. These
limitations of the NIOSH 5040 method can be addressed by the use of real-time
DPM monitoring devices. Although use of real-time DPM monitors is relatively
new in the mining industry, real-time DPM monitors can almost instantly quantify
the generation rate of DPM as well as its relative magnitude, and highlight mine
situations where DPM levels are relatively high for substantial time periods.
Most real-time monitors (both prototypes and commercial units) developed for
determining DPM concentrations in mines have faced serious challenges to accurately
estimate desired DPM concentrations. This is due to their increased vulnerability to
mine atmospheric conditions like oil mist, mineral dust, presence of moisture, and
other particles. Another big challenge in using real-time DPM monitoring devices
is their applicability in different mining conditions and the lack of a standard/unified
calibration method for these units. NIOSH has been closely involved in the develop-
ment of various instruments that measure airborne DPM concentration [65]. Although