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Dangerous Dust: The Silicosis Hazard in American Industry

by Leonard Greenburg, M.D.

Executive Director, Division of Industrial Hygiene, New York State Department of Labor

December 1936


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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.

The third 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.

In considering 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.

IN 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.

In attempting 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.

The following 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.

Occupation Rate per 100,000
All males, occupied and retired 150
Tin and copper miners, all underground workers 1886
Cutlery grinders 1323
Metal grinders 637
Stone workers and slate workers 512
Potters 411
Barmen 402
File cutters 365


Of the 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.

American 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 150
State of Connecticut (male population) 170
Ax factory district (3 towns, entire population) 200
Employes of ax factory (all) 650
Employes of ax factory, polishers and grinders 1900
Employes of ax factory, others 160

 

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