Page 114 - Advanced Mine Ventilation

Health Hazards of Respirable 7

Dusts

Chapter Outline

7.1 Growth of Coal Workers’ Pneumoconiosis 95
7.2 A Basis for Respirable Dust Standard 101
7.3 Prevalence and Cessation of Coal Workers’ Pneumoconiosis 101
7.4 Lifestyle Intervention Program 103
References 104

Coal is a brittle material, and therefore dust is produced when it is mined, crushed, or
reduced in size by any method. Dust has been defined as solid particles smaller than
100 mm(1 mm ¼ 10 4 cm) in size, which can be disseminated and carried by air.
Coal dust when raised into a cloud creates two well-known hazards in coal mines,
namely, coal dust explosion and coal workers’ pneumoconiosis (CWP). For an explo-
3
sion, a coal dust concentration of at least 86.5 gm/m of air is required [1]. Maintaining
a dust concentration in mine air below this level is relatively easy because the coarse
dust particles normally settle in the roadways almost immediately after dissemination.
Explosion hazard of dust and its mitigation will be discussed later in the book.
The fine dust particles, particularly the ones below 10 mm, based on unit density in
size, do not settle easily. In the minus 10 mm range, coal particles are called respirable
dust because these can be inhaled and can contribute to the CWP. It is mostly
composed of coal and silica, but there are 50 other elements and their oxides in it in
very small proportions.

7.1 Growth of Coal Workers’ Pneumoconiosis

The health effects of respirable particles on the lungs are better understood in the light
of the knowledge of the components and functions of the human respiratory system.
The respiratory system consists of a series of branching passages decreasing in size
but increasing in number as shown in Fig. 7.1.
Thus starting with inhalation either through the nose or mouth, air passes in succes-
sion through the trachea, bronchi, bronchioles, alveolar ducts, and finally into the alve-
olar air sacs where gaseous exchange of oxygen takes place [2]. The hairs and small
bones of the nose act as a filter and almost completely filter out particles larger than
10 mm. Particles between 2 and 10 mm in size usually settle on the walls of the trachea,
bronchi, and bronchioles. The particles finer than 2 mm reach the inner parts of the
lungs. The respiratory system above the bronchioles are lined with a hairlike structure,

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