Page 120 - Advanced Mine Ventilation

Health Hazards of Respirable Dusts 101

7.2 A Basis for Respirable Dust Standard

To set a scientific basis for respirable dust standard, one must determine the dust expo-
sure versus health response curve, preferably for each coal basin. This provides a basis
for setting a personal exposure limit (PEL), such that when exposed to this level of
respirable dust for a working life of 30e40 years, the probability of a worker devel-
oping a CWP of category 2 or above is zero. The only scientific study in this area
was carried out in the United Kingdom over a large cohort [17], and the results are
shown in Fig. 7.4.
It clearly shows that the probability of contracting category 2 CWP is zero at 2 mg/m 3
of respirable dust concentration. The United States’ PEL for respirable coal dust was
3
3
thus set at 2.0 mg/m in 1972. It was further reduced to 1.5 mg/m in 2015 to lower
the health risk. However, a monatomic decrease in PEL is not going to guarantee the
elimination of CWP. This will be discussed further in the next article.

7.3 Prevalence and Cessation of Coal Workers’
Pneumoconiosis

Before the enforcement of the new US Coal Mine Health and Safety regulation of
1970, the incidence of CWP was very high, but it has declined drastically since
then. Figs. 7.5 and 7.6 show the progressive decline in respirable dust concentrations
and the prevalence of CWP in US coal mines, respectively [10].

Figure 7.4 Probability that a man starting with no pneumoconiosis (category 0/0) will be
classified as category 2 or higher after 35 years of exposure to various concentrations of coal
mine dust.