Page 119 - Fundamentals of Air Pollution

III. Stationary Sources 89

J. Stone and Clay Products
The industries which produce and handle various stone products emit
considerable amounts of particulate matter at every stage of the operation.
These particulates may include fine mineral dusts of a size to cause damage
to the lungs. The threshold values for such dusts have been set quite low
to prevent disabling diseases for the worker.
In the production o* clay, talc, cement, chalk, etc., an emission of particu-
late matter will usually accompany each process. These processes may
involve grinding, drying, and sieving, which can be enclosed and controlled
to prevent the emission of particles. In many cases, the recovered particles
can be returned to the process for a net economic gain.
During the manufacture of glass, considerable dust, with particles averag-
ing about 300 /xm in size, will be emitted. Some dusts may also be emitted
from the handling of the raw materials involved. Control of this dust to
prevent a nuisance problem outside the plant is a necessity. When glass
is blown or formed into the finished product, smoke and gases can be
released from the contact of the molten glass with lubricated molds. These
emissions are quite dense but of a relatively short duration.

K. Forest Products Industry
1, Wood Processing
Trees are classified as a renewable resource which is being utilized in
most portions of the world on a sustained yield basis. A properly managed
forest will produce wood for lumber, fiber, and chemicals forever. Harvest-
ing this resource can generate considerable dust and other particulates.
Transportation over unpaved roads causes excessive dust generation. The
cultural practice of burning the residue left after a timber harvest, called
slash burning, is still practiced in some areas and is a major source of smoke,
gaseous, and particulate air pollution in the localities downwind from the
fire. Visibility reduction from such burning can be a serious problem.
Processing the harvested timber into the finished product may involve
sawing, peeling, planing, sanding, and drying operations, which can re-
lease considerable amounts of wood fiber and lesser amounts of gaseous
material to the atmosphere. Control of wood fiber emissions from the
pneumatic transport and storage systems can be a major problem of consid-
erable expense for a plywood mill or a particleboard plant.
2, Pulp and Paper

Pulp and paper manufacture is increasing in the world at an exponential
rate. The demand for paper will continue as new uses are found for this
product. Since most paper is manufactured from wood or wood residue,
it provides an excellent use for this renewable resource.