Page 116 - Advanced Mine Ventilation

Health Hazards of Respirable Dusts 97

walls swell up, become less distensible, and break down, leaving cavities 1e4mm in
diameter. This is called pulmonary massive fibrosis and implies grave prognosis, with
death frequently resulting from pulmonary failure or infection with tuberculosis.
In view of the human suffering and financial costs involved, the control of pneumo-
coniosis has become essential. On the basis of the studies made so far, the following
factors seem to influence the disease:
1. Concentration of dust in the air.
2. Size distribution of the dust particles.
3. Chemical and physical composition of the dust.
4. Life style of the subject, such as, smoking habits.
5. Individual’s resistance to pneumoconiosis/lung diseases.
6. Presence of electrical charge on dust particles. More particles are deposited in the respiratory
system if they are charged than if they are uncharged [3]. Freshly mined dust has more free
radicals in it than old dust.
7. Thermal repulsive and evaporative effects in the lungs. The presence of these forces in the
lungs are known but their effects on dust deposition are not fully established [4]. Control
of the disease, therefore, should basically center around the following factors:
a. The maintenance of dust concentration in the mine air below a given level that minimizes
the risk of CWP.
b. Medical supervision of miners on a regular basis.
c. Lifestyle of mine workers.

Engineering control of the disease is thus concerned mainly with the control of dust
concentration in mine air. Most of the major coal-producing countries have established
respirable dust standards for coal mines. The concentration of dust was measured by
the number of particles per unit volume of air in the past. This standard has now
been replaced by the mass per unit volume of mine air on the basis of studies which
indicate that the mass of coal dust deposited in the lungs bears a better correlation
with the total damage caused by the disease [5,6]. Postmortem studies conducted on
a miner’s lungs indicate a strong correlation between the average weight of dust in
the lungs of a miner and the radiological category of pneumoconiosis contracted by
him [7]. To establish a relationship between the dust dose and the growth of pneumo-
coniosis in coal miners, the Pneumoconiosis Field Research group of the National Coal
Board (NCB), United Kingdom, surveyed a population of 30,000 coal miners over a
period of 18 years, beginning in 1952. The dust dose was expressed as mean coalface
dust concentration during the period of observation. The response of a miner to dust
inhalation was measured as the amount of radiological change determined from chest
radiographs taken at the beginning and at the end of the observation period. To mea-
sure the radiological changes quantitatively, CWP has been divided into four cate-
gories, namely, 0, 1, 2, and 3, by the International Labour Office in increasing order
of severity [8]. Each of these categories has been further subdivided into three stages
by the NCB to account for even minor changes in lung conditions [6]. The progress of
disease from one stage to the next has been considered as one step of progression. The
response of a miner to dust inhalation was measured as the number of steps of progres-
sion per million working shifts.