A report on the absence of pneumoconiosis among workers in pure limestone.

It is generally believed that exposure to limestone dust does not present a pneumoconiosis hazard. However, Doig (1955) has recently described cases of silicosis amongst limestone workers after prolonged exposure to high dust concentrations. The limestones concerned contained from 5 to 15% quartz as impurity, and dissolution of the calcium carbonate in the lung would leave a quartz-rich residue which may well have caused the disease. If this interpretation were correct no pneumoconiosis should occur amongst workers in pure limestone. It was decided to test this by radiological and clinical examination of men who should have been exposed to high dust concentrations of pure limestone for long periods of time. The purest limestone found in sufficient quantity for commercial use in the British Isles occurs in the Buxton area of Derbyshire. This limestone is of the Lower Carboniferous age and contains upwards of 97% of calcium carbonate. Its quartz content is usually below 1%. There are many quarries and grinding plants in the area but the basic processes are identical in most plants. The quarried rock is broken by crushers, screened, and dried. The dried product is pulverized and bagged. Dust conditions vary with the type of machinery and ventilation systems inuse. Ingeneral,'the smaller and olderplants are more dusty than the large modern ones. Rotary driers, pulverizers, and bagging machinery produce most of the dust but crushers and conveyors also can be very dusty. The ventilation systems usually discharge the dust into the open air above roof height, and its further dispersal is very much affected by wind and weather. There is a definite haze of dust in many plants and a covering of dust over machinery, ladders, and floors. The faces, hands, and clothing of the workers are covered by a layer of dust. In the course of the survey made in the autumn