Miners Phthisis

MINERS' PHTHISIS. Almost any dust inhaled in sufficient quantity may cause chest trouble, but certain dusts are related to the occupational disease variously known as miners' phthisis, pneumonoconiosis, grinders' rot, potters' rot, stonecutters' rot, etc.

Phthisis-producing Dusts.

Dusts with this association are often referred to as phthisis-producing dusts, because pulmonary tuberculosis plays a more or less important part in this disease and is always associated with a fatal termination and usually with disablement. E. L. Collis has shown that the phthisis-producing dust of far the greatest importance in industry is dust of free silica and the disease is often known as "Silicosis." For a dust to be phthisis-producing it must be comparatively insol uble and inert and the particles must be minute, say from five microns downwards, or about the size of the common pathogenic micro-organisms. Owing to their minute size these particles may be present in air in dangerous concentration without being visible to the eye or in any other way noticeable to the senses, so in a phthisis-producing industry it is expedient to sample the air for dust as one samples for gas in a "gassy" mine.

The Lungs and Dust.

The lungs have a very considerable power of ridding themselves of inhaled particles, and some dusts, like coal-dust, are much more readily got rid of than others while, in the case of a phthisis-producing dust, accumulation readily gets ahead of elimination, so quite small quantities of air-borne dust may be dangerous. It is owing to this cumulative factor that dura tion and continuity of exposure are of importance as well as con centration in the air. While the average incidence of miners' phthisis in the gold-mines of the Witwatersrand is under 3% per annum of the underground population, the incidence rises as high as 1 o% per annum among miners of 13 years' service and over.

A certain proportion of the fine dust inhaled runs the gauntlet of the upper respiratory passages and gets right down into their minute blind extremities, the alveoli. In silicosis as in pulmonary tuberculosis "lesion means arrest" and the dust particles are arrested by being taken up by certain cells often called dust cells. These are phagocytic endothelial cells and, when dust-laden, they aggregate forming masses or pseudo-tubercles on the alveolar walls, under the pleura and in the lymphatic channels which they obstruct. The pseudo-tubercles tend to degenerate and become replaced by fibrous tissue, thus forming the fibroid nodules char acteristic of the early stage of silicosis.

Prevention.

It is the fine dust that matters and, in mines where a phthisis-producing rock is dealt with, the chief sources of fine dust are blasting and rock-cutting with machines. From the point of view of prevention, in industries where blasting is prac tised, the workers should not return to the working-place until after all dust and fume have been blown away. Ventilation with

good currents of dust-free air is the great safeguard because, by treating the air-borne dust as a gas, it can be diluted down towards a safe level. With daily exposure over many years, perhaps about one milligramme of dust per cu. metre of air is a safe level. The fine dust is only a small proportion by weight of the total air-borne particles, but includes t'he majority of particles by enumeration.

A sample of air-borne dust of 2 milligrammes per cu. metre as determined by the method in use on the Witwatersrand corre sponds to about 35o particles of fine dust per cu.cm. of air (counted by Kotze koniometer).. The other great safeguard is "working wet" as the chief source of the dust associated with machine drilling is "sludging" with air. When it is practicable to sludge with water only, machines raise much less dust. Water sprays should be in continuous use and the roof, walls and floor of the working-place kept wet (see MINING).

A machine may be in good order for rock-cutting and in bad order for dust-control and should be inspected from the latter point of view as well as the former. A hand-drill is more difficult to keep in order for dust-control than is the larger machine and it is doubtful if it is possible to secure safe conditions if hand-drills are used dry when cutting phthisis-producing rock. In all phthisis producing industries, apart from working wet, it is wise to think of the fine air-borne dust as a gas and make use of exhaust-hoods and abstractors; while sources of dust escaping to the air should, as far as possible, be located and enclosed.

There are two important factors in the severe forms of miners' phthisis : (I) The phthisis-producing dust.

(2) The tubercle bacillus.

The modern view of pulmonary tuberculosis as met with in the adult population of civilized countries is that it is contracted from an active case by inhalation. Under experimental conditions the presence of dust in the air, together with the tubercle bacillus, renders the susceptible animal much more liable to infection by inhalation. It is on account of this association that, in a phthisis producing industry, one must strive not only to eliminate dust but also to eliminate the tubercle bacillus. The only practicable step towards the latter ideal is to detect and remove the "carrier," i.e., the sufferer from open tuberculosis.

BIBLIOGRAPHY.--Public Health (1915, with bibl.) ; E. L. Collis, Industrial Pneumonoconioses, Milroy Lectures, 1915 (1919) ; Annual Reports of Miners' Phthisis Board and Miners' Phthisis Medical Bureau, Department of Mines and Industries, Union of South Africa; Publications of United States Bureau of Mines, B132, T.P. 372, etc.

(A. MA.)