Lead poisoning and lead absorption

Manufacture of White Lead.

[20]—The usual method in this country is that known as the “Dutch process,” although the German chamber process, precipitation processes, and others, are all practised.

Dutch Process.

—A layer of spent tan is placed on the floor of the stack (a chamber with walls of brick some 25 feet high, and a vertical opening from top to base through which the men enter), upon which are arranged earthenware pots partially filled with dilute acetic acid. Strips of lead are then placed on small square “cockney” pots, or more rarely in the form of folded grids, inside deep, long “castle” pots, and the whole covered with boards, resting on special “bearer pots” containing dilute acetic acid. Ten to fifteen of such layers (blue beds) one on the top of the other are built into the stacks to a height of some 20 feet. When completed, the stacks remain for 80 to 100 days before being emptied. During this period the temperature rises to 75° to 80° C., considerable evolution of carbonic acid gas takes place, and the lead is converted first into acetate and subsequently the white basic carbonate. The layers (white beds) are uncovered and the corroded strips (corrosions) collected by hand. They are placed in trays and carried to heavy steel rollers by means of which and subsequent raking in wash becks the carbonate is detached from the uncorroded central core of blue lead. In many factories corrosions are now conveyed from the stacks to the wash becks or rollers by travelling cranes. The recovered blue lead is removed in a wet state to be remelted and recast. The corrosions, after passing through the rollers and wash becks, are shovelled on to a picking-board and transferred gradually to the grindstones. From the stones the ground pulp passes to the settling becks through several gratings of fine copper mesh. In the form of pulp the material is ladled by hand into bowls for conveyance to the drying stoves. When dry, the contents of the bowl are emptied into barrels and headed, or into hoppers, from whence the material is conveyed to be packed either by hand or automatically by mechanical packers, or to be converted into paint.

Dangers and Prevention.

—In casting the strips, risk does not arise from lead fume, as the temperature at which this is effected (350° C.) is too low for appreciable fume to be given off. Danger here is from skimmings and deposit of them on the floor or into a receptacle unprovided with exhaust draught. Pots in which remelting of the uncorroded cores (returns) is done should be provided with hoods and exhaust, because of the dust given off in stirring and skimming and the spurting which occurs as they are thrown in wet. In making the blue beds, dust arises from particles of white lead adhering to the pots and in the tan bark. Pots, on removal from the white beds, should have all white lead inside them removed by washing in a tank. Screening of the bark should be dispensed with. Emptying the white beds accounts, perhaps, for the largest number of cases, owing to the impossibility, in the present state of knowledge, of dealing with the dust by means of exhaust ventilation, or quite adequately by watering or wearing of respirators. Watering by means of a hosepipe with rose attached is, however, the main safeguard. Substitution of the square cockney pots for the long castle pot is also of moment, as the flat plates of lead form a denser and more porcellanous corrosion than that of the grids in the castle pots. Moreover, in stripping the beds the flat corrosions can be lifted into trays without creating dust, whereas to dislodge the contents of the castle pots may require a sharp tap, and the unglazed portion of the interior surface of the latter retains some carbonate when moistened. Watering requires to be thorough and done with care, or else the softer material of the corrosion may be washed into the tan. No less important is it to water the layers of tan, and at a time while they are yet warm and slightly damp, otherwise the tan becomes so dry that the water runs through, and does not adequately prevent dust formation on its removal. A requirement of the special rules is that the trays for collecting the corrosions shall not stand directly upon the beds. When corrosions contain an undue proportion of lead acetate, they are termed technically “floury,” and much dust may arise from them on watering unless this be done with a very fine rose.

Dust at the rollers and wash becks is usually checked by preliminary immersion of the tray of corrosions in a trough of water, but the extra weight of the water causes this sometimes, in the absence of mechanical arrangements for immersion, to be done perfunctorily. Where there are rollers, the tray is inserted in a small opening above them, the contents saturated by a spray, and then tipped over. This method also may fail to control the dust, as, unless the men engaged in washing the corrosions in the wash beck keep the mass tipped in from piling up in a heap, the contents of the trays are discharged on to the heap, and not into water. In some factories exhaust ventilation at the rollers or wash becks has been necessary.

During subsequent wet processes of grinding danger is mainly from splashing. From the settling tanks the white lead is pumped into filter presses, and the resulting cake is dried. Here the considerable risk from splashing is again almost unavoidable. Concrete floors are necessary. Emptying the stoves involves much handling, with inevitable creation of dust, especially when the bowls are withdrawn from the racks. Risk has been greatly lessened by reducing the height of the shelves to 10 feet and prohibiting the piling of one bowl upon another. Mechanical drying stoves into which men need not enter either for filling or drawing are now commonly met with. Of these there are various types—(1) Horses similar to those common in laundries, which can be withdrawn on rails; (2) small chambers built up one upon another somewhat in the form of gas retorts in a gasworks, heated by steam jackets and coils, each chamber containing only two or three cakes of white lead pulp, the cakes themselves being removed by a mechanical process from the press into the drying chambers; (3) bogies carrying the white lead in bowls on racks made to pass through the tunnel-like stove; (4) drying machines—i.e., closed cylinders fitted with a series of platforms so arranged that they may be charged with white lead on one side, and so fixed as to be turned round by means of mechanical appliances. When dry, the material is discharged into a chute by a series of scrapers into a small enclosed compartment, holding the barrel to be filled. With the drying machine, however, there is considerable risk of dust leakage, especially when the doors are opened. In packing by hand, safety depends on efficient exhaust ventilation when the contents are tipped into the barrel, but a danger constantly present is that, to get through the work quickly, the bowls may be withdrawn from the influence of the exhaust before the last traces of dust have been removed from the bowl. Mechanical packing, by means of a large bladed screw forcing the white lead into the barrel, which as it becomes filled is lowered automatically, is everywhere desirable. An essential condition of this method is that a dust-proof collar should connect the automatic packer with the barrel. Some dust almost inevitably escapes, and a hood and exhaust should be provided, however perfectly the machine is said to act.

Much of the white lead is converted into paint on the premises, being ground in oil either in pug mills, Torrance mills, or under edge-runners. A negative pressure must be maintained inside the casing, which must enclose the stones. Here the conditions are precisely those described under the manufacture of paints and colours. In some white lead works conversion into paint is done without the dangerous process of stove drying, either by drying under a vacuum or by mixing the white lead directly with oil. In the process of grinding the oil incorporates itself with the white lead, and the water is forced out, running away in a clear stream.

Chamber Process.

—In this method, almost universally used in Germany, and adopted in at least one large white lead works in this country, a chamber arranged with numerous sets of parallel bars on which the thin strips of lead are set saddle-wise takes the place of the stack in the Dutch process. Carbonic acid gas and acetic acid vapour act on and corrode the strips. In a period of from eight to ten weeks the corrosions mostly fall to the ground. Such of the strips as do not fall have to be lifted off the bars, having been previously well saturated with water from a hosepipe, and are dropped on to the floor of the chamber. We are not satisfied that working in the dark, confined chamber by artificial light is less dangerous than working on the stacks. Chamber-made lead undergoes practically the same subsequent processes as have been described.

Precipitation Processes.

—These also dispense with stacks and the consequent risks attending work on the blue and white beds, but they substitute another—namely, use of oxide of lead (litharge or the suboxide) as the initial product to be carbonated, with the inevitable danger, in the absence of mechanical contrivances entirely closed in, of shovelling dusty material. In many of these methods, however, mechanical arrangements obviate hand labour or contact with dust in all but the first process.

The Brimsdown process[21], for instance, is automatic and free from dust, except in the initial stage of preparation of litharge in cupellation furnaces. The great risk from the disintegration of this material (see p. 250) by turning it out on the floors is obviated by allowing disintegration to take place in the pots (which must not, therefore, be completely filled), and tipping these when cooled directly into a breaker under powerful exhaust draught. From the bin into which it falls the material is conveyed by dust-proof elevators to (a) screens and packing arrangements when the object is flaked litharge, or (b), in the case of the bulk of the material for manufacture of white lead, by enclosed conveyors to reducers and mixing mills, where reduction and hydration take place. It is then charged automatically into weak solution of acetic acid, and by agitation with carbonic acid gas converted into basic carbonate of lead. From the carbonators pumps force it into filter presses, where the acetate is drained off and washed out by pure water. The cakes of white lead are fed into mixing machines and pugged with linseed-oil until the water has been entirely removed, and finally passed through the roller mills to be packed in casks.

Dry white lead is made by feeding a metal travelling lattice with pulp white lead inside a drying chamber entirely closed in. When dry, the white lead is automatically brushed off, elevated, and automatically packed in a chamber under efficient exhaust draught. In this part of the process, therefore, risk to the workers is very small.

The stringent Special Rules for the White Lead Industry show what other precautions, in addition to exhaust ventilation, are necessary—especially personal cleanliness. The effect of one other factor—casual labour—however, must be referred to. The condition at the present time is very different from that which existed twelve years ago. From one factory in 1899, depending much on casual labour, 111 cases were reported, and from another 72. In an inquiry made by one of us in 1898, information was obtained of the actual number employed on any one date, and of the total number passing through the factories in a year.

Among the firms with regular employment at that time, the incidence of lead poisoning was 60 per 1,000 on the average number employed, and in those with casual employment 390 per 1,000. Work in lead had secured a bad name, and no one who could get employment elsewhere would take to it. Consequently, the class of men applying for work was a low one—men discharged from other employment and those unfitted for skilled labour. Not a few were addicted to alcohol. The work was unskilled, and had the additional advantage to men of that class that much of it was piece work, paid at a good rate, which could be finished as a rule by three o’clock in the afternoon.

Diminution in the number of cases from 399 in 1899 to 34 in 1910 has been brought about mainly by—(1) Improved structural conditions; (2) adoption of mechanical means (cranes, rails, hoists, etc.) for conveyance of material in substitution for hand carrying; (3) exhaust ventilation, where dust arises as in packing and paint-mixing; (4) periodical medical examination; (5) diminution in height of the stoves or adoption of mechanical drying stoves; (6) conversion of white lead into paint by means of direct mixture with oil while in the pulp stage; and (7) substitution of small, square, glazed pots—cockney pots—requiring the lead strips to be placed on them, for the deep castle pots into which the lead grids are folded in the white beds. Prohibition of female employment in the dangerous processes was made prior to the Special Rules of 1899. Their greater susceptibility as compared with men, the special effect of lead on the uterine functions, and the unsuitability of much of the work for women, fully justified the step recommended by the White Lead Committee in 1898.

Earthenware and China.

[22]—The industry includes the manufacture of earthenware, china, tiles, majolica ware, Rockingham ware (teapots), sanitary ware, china furniture, and electrical fittings, and any other articles made from clay; but of the total 6,865 persons employed in lead processes in the whole of the United Kingdom in 1907, 5,834 are included in the manufacture of the first three. And even in the manufacture of earthenware, china, and tiles, the poisoning which occurs is not distributed evenly over the whole of the factories. These number 550, and, taking the period 1904-1908, 5 potteries were responsible for 75 cases, 17 for 119, and 151 for 323, leaving 377 factories out of the 550 from which no case was reported. Incidence seems to depend more on the scale and rapidity of the output of cups, saucers, plates, and tiles, in everyday use, than on anything else.

The number of reported cases year by year from 1900 to 1909 has been as follows:

ALL LEAD-WORKERS IN PLACES UNDER EARTHENWARE AND CHINA SPECIAL RULES. WHOLE OF UNITED KINGDOM (INCLUDING NORTH STAFFORD).

Number of Persons Employed.

Number of Persons Employed.

The processes in so far as lead enters can best be divided into—(1) Glaze; (2) decorative.

1. Glaze Processes.—The charge of glaze is made by weighing out and mixing carbonate of lead with the necessary silicates and silico-borates in the lead house or mixing-room, where wet grinding prepares the mixture for the dipping-tub. “Putters-up” hand the ware to the dipper, from whom “takers-off” place it on boards for removal to the drying still, or place it (in large works) directly on to the shelf of an appliance known as a “mangle,” in which an endless chain carries the ware through a heated chamber. Subsequently superfluous glaze has to be removed from the base, rims, and not infrequently also other parts of the articles. This ware cleaning is performed with a wet sponge or flannel, either while the ware is still moist or by scraping, the particles removed dropping into a vessel of water; or, if the glaze is dry, over a grating provided with exhaust draught. The ware is next removed by the glost-placer on boards, and each piece is separately placed by him in the sagger (fireclay receptacle) and carried into an oven to be fired.

2. Decorative Processes.—Majolica painting is the application of a coloured glaze rich in lead by means of a brush. Ground-laying consists in dusting powdered enamel colour on to a pattern first printed on glazed ware with an oily medium. Colour dusting differs from the same only in detail.

Aerographing (colour blowing) is the blowing on to the ware, by means of a jet of compressed air, coloured glaze, or enamel colour held in suspension in oil or other liquid in a glaze kettle or aerograph instrument.

Dangers.

—Apart from risk inseparable from, and increased by, defective lighting, uneven floors of wood or brick, collection of dust on benches and floors, and the risk entailed in the sweeping of these even when watering is practised, and lack of care and attention to detail on the part of the worker, the following special dangers are incidental to the various processes: In dipping the glaze (except in tiles, where the surface only is allowed to touch the liquid), splashes on to the face and overalls of the dipper, “hander-up,” and “taker-off” (dipper’s assistants), and “threader-up” (in the case of china furniture), especially when, as with plates, there is much shaking of the ware. These splashes dry, and the overalls may become so coated with glaze that every movement, such as carrying boards or leaning against the mangle, crumbles it off as dust into the air. As the dipper shakes the ware, some of the drops are disseminated into the atmosphere as a fine spray. In ware cleaning the work may have to be done so rapidly that it is difficult always to observe proper care, and the worker is tempted to withdraw the article from the range of the exhaust. Sometimes a ware cleaner is seen blowing away with her mouth dust lying on the ware.

Dipping-boards, unless freed from adherent glaze by washing after use, create dust whenever ware is placed on, or removed from, them, when they are handled and placed on or taken off the stillage bars, and when they are stacked. Persons gathering at the mangle are exposed to dust if there is any outward current of air from it. The glost-placer raises a slight amount of dust as he takes the ware from the board and places it in the sagger. The dangerous practice formerly almost universal of rubbing the bottoms and rims of cups, etc., either together (without use of an exhaust) or rubbing them on a piece of leather fixed round the chest, is generally replaced by removal of the glaze on a moist piece of flannel, but it is still possible to find men doing it in outlying potteries. In majolica dipping and painting (apart from the obvious risk of splashing and contamination of the hands), danger arises mostly from scraping the edges and under surfaces of the tiles on to which glaze, when applying the background, has overflowed. The amount of glaze so removed is considerable, and if it is not all caught in the trough of water, the floor becomes an added source of danger.

In all the decorative processes—ground-laying, aerographing, colour-dusting, and grinding of colours for aerographing, etc., the danger is one solely arising from dust.

Prevention.

—Meticulous attention to detail, not only in the provision, but also in the maintenance, of the locally-applied exhaust ventilation, alone can allay the danger in the processes to which dust is incidental, such as ware cleaning, gathering at the mangle, glost-placing, and the decorative processes. The Lead Committee considered that, as there was no rapid method of testing the actual degree of moisture, exhaust ventilation might be required in the case of ware that was not cleaned within fifteen minutes of the application of the glaze. Such a requirement would prevent the practice now prevalent of painting as many as three dozen tiles, piling them one on top of another, and then proceeding to the operation of scraping. No danger attaches to removal of glaze with a damp sponge or flannel, but means must always be at hand for washing and damping them. In the dipping-house, (a) impervious floors should be provided, which could be washed down so as to prevent the risks from sweeping, and from glaze drying, and being raised as dust; (b) partial covering of the dipping-tub to prevent splashing and spray; and (c) substitution for the overalls at present worn by persons in the dipping-house, glost-placers, millers and mixers of glaze, majolica paintresses, and others, of overalls of some light waterproof material which could be sponged, or of aprons of waterproof material worn in front of the overalls. Dipping-tubs and walls and floors in close proximity to them can with advantage be painted red. Dipping-boards should be washed with clean water after every time of use. Automatic machines for washing and scrubbing boards are in use in some factories.

To reduce risk or remove the danger of lead poisoning in this industry, use of low solubility glazes or of leadless glazes are advocated. On this point the Lead Committee say: “The effect of melting the lead with silicious matter amounts to imprisoning it in such a manner as to render it less liable to the action of the acids which it meets in passing through the human body, and in consequence largely reduces the likelihood of its absorption into the blood. If the frit is properly compounded, all but a small fraction of the lead is rendered insoluble, and glazes so made are spoken of as ‘low solubility glazes.’ The finished glaze generally contains from 12 to 22 per cent., or more, of lead oxide, but after the process of fritting with sufficient silicious material only from 2 to 5 per cent. remains soluble.”[A]