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even detectable by the senses. Therefore, industry in general has not become so fully conscious of dust hazards as it has of gas hazards in which there is usually immediate manifestation of harm and frequently sense perception of a contaminated atmosphere.

Roughly, there are two general classes of harmful dusts, those that produce respiratory affections and pulmonary diseases, known generally as pneumonoconiosis, and specifically as silicosis, anthracosis, and asbestosis, and those that produce a general systematic poisoning, as lead, mercury, and arsenic.

Of all the dust hazards the one of most importance at present is exposure to dust that contains silica. When air that contains silica dust is breathed, the particles are deposited in the lungs where through chemical and pathological reactions and processes they produce a condition characterized anatomically by generalized fibrotic changes. This constitutes a disease known as silicosis. It can be present in degrees varying from imperceptible and apparently unharmful to physical impairment and total disability. In addition to being conducive to physical impairment, it also creates a predisposition to tuberculosis.

Injury from inhaling silica-containing dust is cumulative with exposure, and there are indications that it can be progressive even though exposure is terminated. It can be arrested but is seldom retrogressive to the point of complete recovery. This is important from the viewpoint of liability for compensation because significant injury is demonstrable at any time by X-ray examination.

Silica is one of the most abundant materials in the earth's crust. The ores from which most of the metals, such as gold, silver, lead, copper, zinc, are produced, either contain silica or are associated with silica-containing rock. Sand and sandstone are almost pure silica and granite and igneous rocks are high in silica. Exposure to silica-containing dust is thus inherent in metal mining, rock tunneling in coal mining, quarrying, excavation, and sand blasting.

There is little doubt that silicosis is one of the most widespread and important disabling occupational diseases. From a compensation viewpoint it is at present the most important occupational disease. Owing to the slow development of the harmful stages of silicosis, some industries that have been in existence from 10 to 20 years are just now having their first real manifestations of the disease.

In addition to a wide recognition of the disease and an increasing number of legitimate claims for injury, racketeering in compensation has arisen to an alarming degree. This aspect is rapidly creating difficulties in the enactment and administration of laws that provide compensation for this disease. With the rapidly increasing claims, both legitimate and illegitimate, it is difficult to estimate insurance rates and insurance companies are reluctant to accept the risks,

Other forms of pneumonoconiosis are recognized, the most prevalent of these is anthracosis, caused by breathing high-carbon dusts, usually coal dust. There is some question regarding the disabling qualities of coal dust, but in any event it is evident that it is conducive to pulmonary affections of at least a temporary nature. Miners' asthma is common in certain coal-mining regions, but it is probable that this is largely the result of exposure to the dust of silica-containing strata cut by tunnels and in mining the coal.

Silicosis, formerly termed "miners' consumption”, was known to the ancients. In a very general way Hippocrates' Epidemics speaks of the metal digger who breathes with difficulty and has a pain and wan complexion. Pliny, the elder, in his Natural History speaks of the use of respirators to avoid dust inhalation. Agricola, in his famous work, published in 1556, gives a description of diseases of the respiratory organs. Loehniss, in a book on mines and mine workers, published in 1690, makes reference to the dust causing lung diseases.

In modern times, the first important systematic inquiries were begun in Cornwall, England, by a Royal commission appointed in 1902. The commission found that many of the miners had lung diseases. A similar commission was appointed in the Transvaal in the same year to report on the subject of miners' phthisis. This commission found that the disease was common among rock drillers, and the conclusion was that breathing dust was the cause.

For many years the Bureau of Mines has been aware of the influence of dust exposure on health and has conducted many investigations to ascertain ways of reducing the hazard. As a result of these studies, the Director of the Bureau of Mines on June 2, 1934, approved decision no. 26 of the Mine Safety Board of the Bureau, entitled "Reducing the Amount of Harmful Dust in Mines and Tunnels.” This decision states:

In the interest of health in mining and tunneling wherever dust is produced which is of such character and in such concentration in the air of the working place as may be harmful to breathe, the United States Bureau of Mines recommends :

That the dust produced be so wetted, trapped, or otherwise treated and the place where men working be so ventilated that there shall not be a harmful concentration in the air of the place.

PAST STUDIES OF THE BUREAU OF MINES RELATED TO SILICOSIS

One of the important matters with which the Bureau of Mines was charged in its organic act was the improvement of health conditions of miners. Shortly after the organization of the Bureau, the first director instructed the chief mining engineer to canvass the problems in the metal mines field. The leading mining men in the "hard rock” districts were unanimously agreed that one of the most important, if not the most important, problem related to the health of miners in certain districts. Consequently, the Director made an arrangement with the Surgeon General of the United States Public Health Service for the detail of surgeons to the Bureau of Mines to cooperate with the engineers for investigating the extent of occupational diseases, especially lung diseases, among miners, their causes, and remedial measures.

At the request of the Secretary of the Anti-Tuberculosis Society of Jasper County, Mo., and the State Board of Health of Kansas, the Bureau of Mines in 1914 and 1915 made an investigation of the relation of the amount of siliceous dust in mines to the prevalence of pulmonary diseases among miners in the Joplin district.

Mr. GRISWOLD. Is silicosis prevalent in the Joplin lead and zinc district ?

Mr. FINCH. Yes; but it has been decreasing to a large extent. It was very serious at the time the investigation was undertaken. I may add that silicosis is liable to be prevalent in any mine where wet drilling is not pursued.

These results were published in Bureau of Mines Technical Paper 105 and Bulletin 132. This study revealed high concentrations of dust in the mines and a high percentage of silicosis and tuberculosis among the miners. Shortly after this, zinc and lead ore was discovered 31 miles southwest of the Joplin field in what is now known as the Picher district. The development of the new field offered the mining companies an opportunity to put into operation some of the recommendations made by the Bureau after the Joplin studies.

After the new field had been in operation a short time, the mining companies asked the Bureau of Mines to ascertain if the measures adopted for the prevention of silicosis were adequate. Early in 1923 the Bureau began a study which was completed in 1925. The results showed considerable decrease in the amount of atmospheric dust in the mines and an improvement in many mining practices, with a definite lessening of silicosis, but there was still sufficient dust to produce silicosis in persons engaged in certain types of work.

As a result of its Joplin study in 1914 and 1915 the Bureau recommended that all miners be examined yearly as a check on the development of silicosis and tuberculosis and to protect the workmen by eliminating those with infectious diseases, especially tuberculosis, since persons that have acquired silicosis are much more susceptible to tuberculosis than nonsiliocotic workers. In order to carry out this recommendation and for the purpose of educating mine operators and workmen in the value of the examinations, a small clinic was organized and operated by the Bureau of Mines with the aid of the Tri-State Zinc and Lead Ore Producers Association (Oklahoma, Missouri, and Kansas) and the Picher Oklahoma Post of the American Legion.

In 1926 more men were applying for examination than the small force at the clinic could handle. In 1927 the additional funds necessary to expand the work of the clinic in the Picher field were supplied by the Metropolitan Life Insurance Co. and the Tri-State Zinc and Lead Ore Producers Association cooperatively through an agreement with the Bureau of Mines.

On June 30, 1932, the cooperative studies were completed and the clinic was turned over to the Tri-State Zinc and Lead Ore Producers Association who have operated it since that time. In 1933 the secretary of the association stated that during that year the saving in compensation costs more than paid the operating cost of the clinic.

From 1928 to 1931, when the Bureau was in charge of the clinic, silicosis and tuberculosis decreased as follows: 66.55 percent in silicosis plus tuberculosis, and 82.70 percent in tuberculosis. This reduction in compensable diseases, with considerable saving to both employees and employers, is due in large measure to the success of the program outlined in 1927. These results have incited industries in other districts to consider taking up the work, following the Bureau's methods.

The success of the Joplin inquiry led the Bureau of Mines in 1916, in cooperation with the Public Health Service, to organize a similar inquiry into the health conditions in the copper mines of

the Butte district, Montana. The Butte investigations were continued for four years with the hearty cooperation of the local mining people. The findings are reported in Technical Paper 260. A review in 1925 showed that enormous advances in hygienic conditions had been made by the mining companies, advances probably greater than those achieved by any other large mining district in the United States in a similar period. (See Bulletin 257.)

Air-borne coal dust not only contributes to respiratory illness but also settles throughout the mine and constitutes an explosion hazard. In coal mines that are rock-dusted for prevention of coal dust explosions, the Bureau has urged that the rock-dust contain no considerable amount of silica (Report of Investigations No. 2606).

In 1924 and 1925, engineers of the Bureau of Mines collected dust from the air of 15 representative coal mines in 6 coal-mining States. Certain of the results obtained are given in Report of Investigations No. 2793, Sources of Dust in Coal Mines.

The chief method of preventing dust is to liberal use of water at the face of the workings to prevent the formation of dust at its source. Forbes and Emery showed that after water had been applied to cutter bars of coal-cutting machines the amount of dust was reduced to one-seventh of that raised by dry cutting. Moreover, samples taken out by the face of workings where water was used plentifully at the face show a decided decrease in the amount of dust over mines exclusively using dry methods. Physical examinations of the miners were correlated with these underground studies and the personal history of the miner insofar as possible.

During 1932 these earlier investigations were extended by a study of the effect of coal dust on the miners of West Virginia. Physical examinations and X-rays were made of about a thousand miners, and the concentration of atmospheric dust was determined.

Harmful dusts occur in the air of most metallurgical plants. In 1916 and 1917 the Bureau of Mines studied the atmospheric dusts in steel mills and published its findings in Technical Paper 153. this report ways for reducing the hazards are discussed. In its general studies of brass-foundry problems, the dusts created in melting, pouring, grinding, and polishing were considered and discussed in Bulletin 73.

When the Bureau first initiated dust studies there was no method whereby the harmful properties of dusts could be determined in a reasonable time. Animals exposed to dust-laden air do not show results for 1 or 2 years. In cooperation with the Public Health Service, a method was developed in the Pittsburgh laboratories of the Bureau of Mines which indicates in a few weeks whether inhalation of a dust is likely to produce a fibrotic condition in the lungs.

Beginning with its first investigations in 1914, the Bureau of Mines has been interested in the quantitative estimation of the amount of dust in air. It has made continuing studies of various methods proposed for dust collection, and from these has developed instruments that best suited its needs. The impinger, developed cooperatively by the Bureau of Mines and the Public Health Service, has been widely adopted and now is the method used by the larger agencies studying atmospheric dust.

The investigations of dust-sampling methods and the devices developed are described in Technical Papers 105 and 278, Bulletin 132, Report of Investigations No. 2392, Information Circular 6048, and United States Public Health Service Bulletin 144.

As an aid to the development of safe and serviceable respirators for the protection of workmen against harmful dust exposure, and at the repeated urgent requests of industry, the Bureau of Mines has developed a schedule (schedule 21) giving the minimum requirements which a dust respirator must meet to give complete protection to the wearer. Eight devices, voluntarily submitted to the Bureau by their manufacturers, have been tested and have passed these requirements. As a result, workers in dutsy trades now have available protective devices much more efficient than any formerly marketed.

Mr. RANDOLPH. It is my understanding that not until late in 1934 did the United States Bureau of Mines officially approve a respirator.

Nr. YANT. That is correct. It was even later than that, although we did conduct studies before that showing how they could be made, their efficacy, and which ones were, in our opinion, good. Respirators are good and bad, and much earlier than 1932 we showed which types were, in our opinion, good and which types were bad. Only since 1934 have we had an official approval for those respirators which must pass our standards.

Mr. RANDOLPH. The reason I bring that up is, after all, it is comparatively a new science, this coping with silicosis and associated diseases in the mining industry; is that true?

Mr. YANT. Yes. Something had been done, but there is much more to do.

Mr. MARCANTONIO. The fact is, nevertheless, respirators were used before 1932?

Mr. Yant. Yes; but they were not so effective as they are now.

Mr. MARCANTONIO. The Bureau of Mines made some recommendations, issued some instructions, as to which were good and which were not so good respirators, did it not?

Mr. YANT. Yes.

Mr. MARCANTONIO. A contractor who had a job under way prior to 1932 could very readily have obtained the information with regard

irators if he had been interested; is not that right? Mr. YANT. Yes. Mr. Finch. The gentleman I called on to answer the questions is Mr. William P. Yant, expert of the Bureau of Mines on dust studies and he is also superintendent of the Pittsburgh experimental station.

Mr. Yant. The date the gentleman was seeking is 1926.

Mr. MARCANTONIO. And that was 4 years before this tunnel was started.

Mr. Dunn of Pennsylvania. Before 1926 mine operators and tunnel constructors really knew that water would reduce hazards caused by dust in mines and tunnels; did they not?

Mr. Finch. Yes. A drill which has a jet of water passing down the center of the drill to wet down the dust was invented years ago.

Mr. MARCANTONIO. The difference between dry and wet drilling from the standpoint of protecting the welfare and lives of the workers was well known to all persons engaged in mining or tunnel operations after 1914 or 1916, was it not?

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