Page 227 - Advances In Productive, Safe, and Responsible Coal Mining

206 Advances in Productive, Safe, and Responsible Coal Mining

several real-time DPM monitoring devices are now in use, the following section
focuses on the FLIR Airtec. This is a commercial real-time monitor that has been sub-
stantially tested under different mining conditions and has shown to function
satisfactorily.
The Airtec measures the EC component of DPM. It has been tested in the labora-
tory and in different mining conditions where its performance was reported to be
satisfactory [66–72]. The Airtec has four key components: an impactor, a filter, a
pump, and an optical measuring circuit. Air is drawn at a set flow rate through an
impactor and through a filter within the instrument, collecting EC from the air sample.
The light intensity transmitted through the filter is then measured by an optical sensing
circuit. Increase in EC accumulation on the filter cassette causes the output voltage
to decrease. Laser absorption is related with EC concentration by comparing the
drop in voltage due to EC accumulation with a calibration curve. The monitor pro-
vides a five-minute rolling average of EC concentrations, which is calculated by
recording a data point every minute. This also provides eight-hour time-weighted
average (TWA) EC concentrations. Laboratory results showed that mineral dust
can interfere with the monitor only in the absence of a size selector; whereas no
influence of oil mist or humidity was observed. The monitor has not detected the pres-
ence of cigarette smoke unless DPM was already present on the filter; however, in
enclosed cabs where the operator was smoking cigarettes, sampling results indicate
that smoke has been shown to cause a bias to the measurement of the Airtec. In
laboratory testing, the Airtec instrument meets the NIOSH accuracy criteria [71].
Khan and Gillies reported some difference in results obtained by utilizing the Airtec
and NIOSH 5040 measurements under similar mining conditions [73]. Khan suggests
a modified calibration method for Airtec monitors when used to estimate DPM
from exhausts produced in equipment burning a fuel with a high percentage of
biodiesel [74].

11.7 Controlling DPM in mines

DPM is essentially one of the critical constituents of the mine air mixture and control
of DPM concentrations is an important aspect of mine ventilation. DPM is a complex
diesel exhaust mixture that has deleterious health effects and the accurate measure-
ment of DPM is a challenging task. In order to control a miner’s exposure to
DPM, there is no single best available option. Thus, the best approach is to adopt a
combination of all control strategies and technologies that are described in this text.
There are many different ways to control DPM in mines. Some approaches focus on
the design and types of diesel engines, some highlight the need for adequate ventila-
tion, some enforce the concept of exhaust after-treatment devices, some encourage the
use of alternative fuels, and some promote environmental cabs and/or PPE. Different
control technologies and strategies adopted in the mining industry to control the
concentration of DPM in underground mines are categorized in the following five
sections.