Dust: The Silicosis Hazard in American Industry
by Leonard Greenburg, M.D.
Executive Director, Division of Industrial Hygiene, New York State
Department of Labor
Since inhaled quartz dust is the causative
agent in producing silicosis and since silicosis is a chronic
disease, it follows that the more quartz dust inhaled the more
rapid the rate of the disease's development. A person exposed
to a dust containing 95 percent quartz, as in sandblasting castings,
is exposed to a greater risk than the worker in a coal mine where
the quartz concentration may be only 2 or 3 percent.
A second controlling
factor is the duration of exposure. It is obvious that in two
years of occupational exposure a worker will inhale about twice
as much quartz dust as in one year in the same employment.
major factor in determining the amount of quartz taken into the
lungs is the concentration of dust in the atmosphere. If we examine
workers in a very dusty establishment and those in a less dusty
plant and study our results, we shall find that in the first group
silicosis supervenes earlier in occupational life, and the rate
of silicosis incidence is higher than in the second group, comparing
workers employed equal lengths of time.
the concentrations of dust it must be borne in mind that particles
of all sizes may not gain access to the lungs. Only those small
enough to reach the terminal air sacs do real damage. These particles
range in length from 1/2500 of an inch down to 1/50,000 of an
inch. There is one exception to this statement, asbestos dust,
which will be considered later.
attempting to estimate the silicosis hazard of a l given occupation
the investigator must always bear in mind these factors: the quartz
dust content of the air, the concentration of particles per cubic
unit of air, the duration of exposure, the size of the particles
present. There is still another important factor, not of the environment
but rather of the individual. This is the element of personal
susceptibility. It has been noted by many investigators that workers
in the same plant, at the same task and at contiguous workplaces
or benches often do not develop silicosis in equal degrees. In
fact one worker may be an early victim of the disease while his
neighbor is comparatively free from it. Personal susceptibility
appears to play a major role in the development of silicosis.
This qngle of the problem presents interesting grounds for speculation
and research. The industrial statistical studies discussed later,
eliminate the element of variations in susceptibility by including
large groups of workers.
to show the influence of dust inhalation on mortality one naturally
turns to the mortality returns of the United States, England and
Wales. But silico-tuberculosis, as a rule, runs a rapid course
terminating fatally, and practically all silicosis deaths are
listed as tuberculosis in these tables.
table, from the report of the registrar general, presents the
standardized respiratory tuberculosis mortality rates for 1921-1923
for England and Wales, and compares the eight occupations having
the highest mortality rates from tuberculosis with the rate for
all occupied and retired males.
||Rate per 100,000
|All males, occupied and retired
|Tin and copper miners,
all underground workers
|Stone workers and slate workers
eight occupations listed, all except one are associated with
the inhalation of quartz dust. It will be observed that tin
and copper underground miners have a tuberculosis rate more
than twelve times that for all occupied or retired males,
and file cutters who work on sandstone grinding wheels largely
composed of quartz have a tuberculosis rate of more than twice
that of all occupied and retired males.
statistics corroborate the findings of the British investigators.
Some years ago Dr. William H. Drury, then in the department
of public health at Yale, reported a mortality study of ax
grinders in a Connecticut factory. With the help of the plant
physician who had been there over twenty years, it was possible
to corroborate all the death returns for the twenty years
1900 to 1919. The grinding wheels used in this factory were
of natural sandstone with a very high quartz content. This
table compares Dr. Drury's findings with the tuberculosis
deathrates for Connecticut, for the district, and for the
other employes in the same plant:
|District or Group
||Death Rate per 100,000
|State of Connecticut
|State of Connecticut
|Ax factory district (3 towns,
|Employes of ax factory (all)
|Employes of ax factory, polishers
|Employes of ax factory, others