Page 179 - Advanced Mine Ventilation

Diesel Exhaust Control 159

The National Institute of Occupational Safety and Health (NIOSH) has identified
diesel particulate matter (DPM) as a potential human carcinogen, but in-mine experi-
ence over the past 50 years does not provide any epidemiological evidence for such
risks. A recent study in Australian coal mines, many of which are partially dieselized,
determined that the standardized mortality ratio (SMR) for lung cancer in a large
cohort of miners was only 78% of that in the general population [3]. A parallel study
in highly dieselized German potash mines (with no confounders, such as, silica, radon,
arsenic, etc.) found similar results for the incidence of lung cancer [4]. Thus, DPM at
prevailing concentration levels does not appear to create any additional health risks.
Apart from the lack of substantial epidemiological data, another difficulty in establish-
ing any in-mine personal exposure limit (PEL) in the coal mines is the lack of instru-
ments that can accurately measure the DPM concentrations. Previous experience with
the coal mine dust PEL also dictates that any PEL for DPM must be based on gravi-
metric measurements.
In noncoal mines, the combustible fraction of respirable dust can provide a good
measure of DPM, but this obviously will not work in mines where combustible min-
erals are being mined. The elemental carbon technique that differentiates between the
fraction of elemental and organic carbons in coal dust and DPM cannot be utilized uni-
versally because neither the composition of the coal mine dust nor that of DPM is al-
ways the same. Many other techniques, such as carbon isotope ratio analysis, Raman
spectroscopy, and electron spin resonance, also suffer from a similar shortcoming. The
size cutoff-based instruments measure everything in mine air below a certain size (0.8
or 1.0 mm). This can be a useful instrument if there was a TLV for all submicron dust
particles in the mine atmosphere but is useless if it is used to measure DPM only.
Table 11.2 shows the major components of DPM. It is generally believed that the
polynuclear hydrocarbons attached to solid carbon particles are the potential carcino-
gens in DPM, but their TLVs are yet to be established. Under these circumstances, the
most prudent option is to minimize the concentration of DPM in mine air using state-
of-the-art technology and introduce diesel engines in all underground coal mines to
improve safety by removing ignition, fire, explosion, and tripping hazards related to
the use of trolley wire and other electrical equipment.

11.2 Diesel Particulate Matter Standards

In spite of the uncertainties discussed earlier, many countries have set a standard for
ambient DPM. Table 11.3 shows the details.

Table 11.2 Major Components of Diesel Particulate Matter (DPM)

DPM
Solid carbon Liquid and solid hydrocarbons include Sulfates Moisture
polynuclear aromatic hydrocarbons