Lead poisoning and lead absorption

by Sir Thomas Morison Legge; Kenneth Weldon Goadby

During the ten years 1900-1909 the number of reported cases from the manufacture of red lead was 108, of which 47 were attributed to work at the furnaces, 43 to packing and sieving, and 16 occurred among general labourers, part of whose duty it was to sweep up the floors. Collis estimates the attack rate in the five years 1905-1909, in a certain number of factories employing 171 persons, at 50 per 1,000. Reference to the table on [p. 48] shows that the proportion of those suffering from encephalopathy is higher than in any other industry—an observation previously noted by Layet[9].

Dangers and Prevention.

—Danger is practically limited to escape of dust in (1) raking the charge out from the hearth on to iron trolleys, (2) sieving, and (3) packing. In all these operations exhaust ventilation is essential, and for sieving and packing the installation requires to be designed with especial care, so as to be able to keep within the sphere of the exhaust the spading and shovelling of the material, in very fine state of division, into the cask. Sometimes the material is elevated from pits, and eventually packed by mechanical means into barrels resting on a jolter. Unless the elevators are quite dust-proof, and the collar hermetically seals the connection of the shoot with the barrel, the vibration of the heavy machinery and pressure of air inside the casing will cause dust to escape.

Red lead can be, and is, now made on an extensive scale in such a way that all operations, from commencement with pig-lead to the final packing, are carried out by mechanical means so entirely closed in that the worker does not come into contact with the material. The person who then may be affected is the fitter attending to repairs of the machinery. The pig-lead is melted, stirred, and mixed in a covered-in melting-pot. The massicot which is formed is drawn off by an exhaust into a hopper, from the bottom of which it is fed mechanically on to the floor of the furnace. Mechanical rabbles stir it from the centre to the outside of the furnace floor, from where it is conveyed, under negative pressure, to the hopper of a grinding mill. From here it is again similarly fed into another furnace. The exhaust pipe from this furnace collects the finished product, carrying it mechanically to a hopper which automatically feeds the red lead into casks. Negative pressure throughout prevents escape of dust.

Manufacture of Litharge.

—Pig-lead is placed in a cupellation furnace, and constantly stirred and raked over to cause entire oxidation, and then is either raked out or run out from the furnace hearth into moulds, and allowed to cool in the form of large balls. These balls, of a roughly crystalline nature, are deposited on the floor, where they are exposed to the air. Disintegration is accelerated by breaking up the large fragments by hand. Subsequently the material is placed in a disintegrator for fine division and packed.

Dangers and Prevention.

—Manufacture of litharge may cause a greater amount of dust than any other process with which we are familiar. The nature of the operations is such that it is impossible at all stages to control this dust. Danger is greatest in the early operations of shovelling up the disintegrated powdery material from the floors into receptacles, and in discharging the contents into the disintegrating machine. The work is heavy, and a respirator is with difficulty worn. A movable hood attached to a flexible duct in connection with an exhaust which could be moved from place to place on the floor suggests itself, but when tried it has not effectively controlled the dust, owing to both the trouble involved and the difficulty of bringing the exhaust near enough to the work. When once the material reaches the disintegrator, exhaust over the hopper, and in connection with the enclosed sifter and grinder and packing machine, can readily be secured. Bins should be provided for the litharge lumps, so as to avoid trampling the powder underfoot, and covered barrows for removing the semi-powdered material. Alternation of employment lessens risk, and should be always arranged. In any new plant the possibility of automatic methods of carrying out the process as far as possible should be considered.

Sheet Lead and Lead Piping.

—This industry also is not infrequently carried out on smelting premises. To make lead piping, molten refined lead is run into a cylinder containing an adjustable mandrel in its centre. The cylinder is forced by hydraulic pressure against a hollow ram having an adjustable orifice to form the desired thickness of pipe. In the case of sheet lead the thick plates are gradually reduced to the desired thickness by pressure of heavy steel rollers.