Lead poisoning and lead absorption

On the subject of the use of leadless glazes, the Committee conclude that in all classes of pottery ware a great many articles can be manufactured in a very high state of perfection, with reduction in the cost of production of certain classes of common ware, such as jampots and Persian painted ware; but that in certain other classes, owing to the excessive number of “seconds,” their use would entail increased cost or sacrifice of quality, so much so as to involve loss of important markets; and, finally, that certain kinds of ware, in consequence of difficulties relative to accuracy in reproducing old patterns, colours, or methods of decoration, cannot at present be made at all without use of lead.

In the case of manufacturers who are able to conform to the Thorpe test of low solubility—i.e., glaze which yields to a dilute solution of hydrochloric acid not more than 5 per cent. of its dry weight of a soluble lead compound, calculated as lead monoxide (PbO)—important relaxation of certain special rules are allowed, such as limitation placed on the employment of females and young persons, and periodical medical examination of the workers.

H. R. Rogers[24], one of H.M. Inspectors of Factories, Stoke-on-Trent, has worked out a simple test to show approximately how much lead has been used in the glaze of a piece of pottery. Thus, by treating glazes with hydrofluoric acid for forty seconds, absorbing the liquid with filter paper, precipitating the lead on the paper as the sulphate, dissolving out the sulphate soluble in water, and then precipitating the lead on the paper as sulphide, stains are produced varying, in depth of colour, according to the proportion of lead in the glazes concerned (see Plate IV.).

Briefly summarized, the recommendations of the Potteries Committee in regard to the processes are—

Manufacture of Glazes.—No handling of white or red lead without at least 5 per cent. of added moisture, and no weighing out, etc., nor employment in the room, to be allowed within thirty minutes of such weighing out, etc., without the wearing of a respirator.

Lawning—i.e., straining glaze so as to remove insufficiently ground material through a fine lawn sieve—to be done by an adult male only, except where less than a quart of glaze is lawned.

Dipping.—Impervious floors sloped towards a drain to be cleaned by an adult male, after work has ceased, with a jet of water and a mop. Walls adjacent to dipping-tubs to be tiled or painted with washable paint, and cleaned daily. Dipping not to be done where artificial light is necessary during hours of daylight.

Threading-up and Thimble-picking to be done in a room sufficiently separated from any place where scheduled processes are carried on.

Drying Ware after Dipping.—The same requirement as to floors as in dipping-house.

Boards.—To be cleaned with clean water by an adult male after each time that dipped ware has been placed on them and before subsequent use. Boards for use in lead processes to be painted red at the ends.

Mangles.—Ventilation to be so arranged as to maintain a flow of air into the hot chamber from the workroom. Mangle shelves to be thoroughly wet cleansed once a week.

Ware Cleaning.—Local exhaust ventilation to be applied except when the process is carried on entirely with use of wet materials (damp sponges, etc.), or when done within fifteen minutes of application of glaze. Troughs to be provided to collect glaze, and to be cleaned out and supplied with fresh water at least once a week. The floors and standard of lighting to be the same as for the dipping-house.

Glost-placing.—Boards to be treated as already described. Floors to be impervious. Women, young persons, and children to be excluded, except that women to be allowed to place china furniture and electrical fittings.

Majolica Painting and Mottling.—A sponge and clean water to be placed beside each paintress; special washing accommodation in the painting-room or adjoining it; splashes to be removed immediately by wet sponging. Work-benches and floors to be subject to the same conditions as potters’ shops.

Flow Material—i.e., the substance usually containing much lead in the form of powder and placed in the sagger to cause certain colours applied to biscuit ware to run slightly—to be weighed out in front of an exhaust draught and delivered to the glost-placer by an adult male.

Ground-laying, colour-dusting, and aerographing to be done under locally applied exhaust ventilation. Proper receptacles to be provided for cotton-wool used and waste cotton-wool to be burnt. No short-sighted person to be employed to do either glaze or colour blowing, unless wearing suitable glasses, and certificate to this effect to be entered in the Health Register.

Litho-Transfer Making.

[25]—Transfers for the decoration of earthenware and china are made in special factories, of which there are seven, employing 257 persons. The patterns are impressed in the ordinary chromo-lithographic fashion, but as the enamel colours, containing high percentages of lead, are dusted either mechanically in the machine, or by hand by means of a pad of cotton-wool, danger from dust is great in the absence of maintenance of a negative pressure inside the dusting machine and an efficient exhaust draught behind the bench where the final dusting with flour, to remove the superfluous colour, is done. In one factory, before a fresh colour was applied to the adhesive pattern on the sheets, the machines had to be cleaned as far as possible of the previous colour used. To do this it was necessary for the attendant to enter a closed chamber at the back of each machine, so as to supply the powder to the hoppers which feed the rollers, or to clean them by means of a brush, sometimes as often as every half-hour. The upward exhaust ventilation applied to the interior of the machine tended to draw the dust created in brushing past the worker’s face, and led to severe incidence of poisoning. The remedy suggested by Pendock[26] was to dispense altogether with the need for entering the chamber, to maintain a slight negative pressure inside the machine by downward exhaust, and to remove the dust by means of a small vacuum cleaning plant.

At the same factory the flouring bench was in the same room as the machines, and the locally applied exhaust drew its air-supply from the general atmosphere of the room. Apart from faulty arrangement of the exhaust ducts leading to effects of too local a character, dust was drawn from other parts of the room, including the machines, so much so as to necessitate frequent cleaning of the glass hoods. Poisoning among those employed in flouring occurred. To remedy this, an air-grid with curved inlets at intervals of 2 inches apart, leading into a trunk in connection with a fan, was placed along the back of the bench and under the top of the glass hood. In order, however, that its action should not interfere unduly with the general ventilation of the room, but be, in large measure, independent of this, a somewhat similar grid, introducing air from the street outside, was fitted along the front of the bench. The whole arrangement was operated by one suction fan. Ten cases occurred in this factory in the year before this arrangement was carried out. In the three years since, three cases only have been reported. In the ten years 1900-1909, 48 cases were reported among 257 persons employed.

Vitreous Enamelling.

[27]—Surfaces, such as sheet iron for advertisement signs, cast iron for baths and gas stoves, copper for copper letters and tablets, brass for jewellery, and glass for lettering and decoration, are treated with glaze or enamel colours, which, either in the mode of application or subsequent treatment before final vitrefaction, give rise to dust.

In the manufacture of advertisement signs, glaze is swilled on to the sheet of iron. After drying, it is fired or vitrified, and upon this surface as many other coats of glaze are applied as may be wanted. As soon as the colour is dry, lettering is effected by brushing away the dried (but not fired) glaze exposed through stencils.

Dangers and Prevention.

—Exhaust ventilation for the removal of the dust is essential, but it is, unfortunately, unable to draw the dust away when brushing is done at a distance of more than about 18 inches from the exhaust opening. And some of the plates required are very large. No exhaust-pipe has yet been invented which will follow the hand of the worker without impeding movement. In consequence of severe incidence of poisoning, mainly on young women who do the work of brushing, when the process was first introduced with enamel glazes containing from 15 to 75 per cent. of lead, manufacturers quickly turned their attention to use of enamels free from lead. For this class of work they appear to have been entirely successful, and now lead poisoning is almost a thing of the past. Thus, of 122 samples examined in 1910 from factories claiming exemption from the regulations by reason of the use of enamels containing less than 1 per cent. of lead, excess was found in three only[28].

Porcelain Enamelling.

—The cast-iron bath or stove is heated to redness in a muffle furnace. On withdrawal from the furnace it is placed by the helpers on a table capable of being turned in every direction. Enamel powder is then dusted on to the heated metallic surface through a sieve attached to a long wooden handle, held by the duster, who protects himself from the intense heat by a mask and an asbestos cloth covering.

Dangers and Prevention.

—The heated column of air carries up much of the powdered glaze as it is unevenly distributed by jolting the handle of the receptacle, and in the absence of very efficient exhaust ventilation this dust will, as the current of air strikes the roof and cools, fall down again. The hood placed over the bath must have steep sides and be brought down as low as is possible without interfering with work, and the duct leading to the fan must be unusually wide, so as to be able to cope with the up-rush of heated air. If the sides of the hood be shallow, not only will the dust fail to be removed, but the hood itself may become so hot as noticeably to increase the discomfort from heat to which the men are exposed during the three or four minutes, five or six times an hour, that the dusting operation lasts. A method has been patented by M. Dormoy of Sougland[29], Aisne, France, for carrying out automatically in a closed chamber the process of dusting on to small red-hot castings, such as are required in the manufacture of stoves. It is not applicable for baths.

Occasionally, in the case of small castings, again, the enamel is sprayed on by means of an aerograph. For this excessively dangerous process we have seen simple and ingenious devices for carrying it on quite safely in a space under negative pressure, and covered in except for the necessary openings through which to work the spray (see Figs. 12, 13, 14).[A]

White enamel powders free from lead are used entirely by some firms, but the black and coloured enamels on stove grates contain lead. A frit analyzed in the Government Laboratory was found to contain 26·66 per cent. of lead oxide. The fact that all the lead used is in the form of a silicate, even although the silicate is readily soluble in dilute acid, tends, we believe, to cause incidence of poisoning to be less than might have been expected from the amount of dust often present in the air, and attacks, when they occur, to be less severe, as a rule, than they would be were raw carbonate of lead alone used. For the arduous work entailed the men are specially selected. Despite their exposure to lead dust, the majority continue to work for many years without marked signs of lead absorption. The management should provide a suitable room for the men to cool themselves in the intervals of dusting.

Manufacture of Electric Accumulators.

[30]—Electric accumulators are secondary batteries which serve for the storage of electricity, in order to allow of a current when desired. A primary battery is one in which the materials become exhausted by chemical action, and, unless a portion or the whole of the materials is renewed, fails to supply electricity. The secondary battery becomes exhausted in the same way, but the chemical contents are of such a nature that it is merely necessary to pass a current of electricity through the battery (charging) in order to recharge them. In the accumulator battery the positive element is peroxide of lead, and the negative element spongy lead. The elements—several positive connected together and several negative—are placed in dilute sulphuric acid contained in vessels of glass.

The form of accumulator in almost universal use now is the pasted plate, but it varies greatly in size, according to the use for which it is required. It may be either large, to act as an equalizer or reservoir of current in electric-lighting installations, or quite small for ignition purposes in motor-cars. The litharge smeared on to one plate becomes converted into the positive element, peroxide of lead, during what is called the “forming process” (passage of the electric current through the dilute sulphuric acid solution in which it is placed), and red lead smeared on to the other becomes spongy lead to form the negative.

The industry gives employment to about 1,200 persons. Plates are first cast in moulds from a bath containing molten lead or of lead with admixture of antimony. Irregularities in the plates so cast are removed by a saw or knife (trimming), and sometimes filed or brushed with a wire brush. The interstices in the plates are next filled in by means of a spatula with paste of litharge or red lead, as the case may be, which has been previously mixed either by hand at the bench or in a special mechanical mixing machine. After drying, the plates are removed to the formation room to be charged. To allow of the passage of the current, positive elements are connected together, and negative also, by means of a soldering iron or, more frequently, of an oxy-hydrogen blowpipe flame. After formation is complete the plates have to be built into batteries, or “assembled.” Tailpieces, technically known as “lugs,” have to be connected with each plate, effected usually by the oxy-hydrogen blowpipe flame. Finally, a connecting bar of lead is cast on or burnt on to the lugs.

Dangers and Prevention.

—In casting, danger is mainly from dust in depositing the skimmings, and from fume also when old accumulator plates are melted down. For these reasons exhaust ventilation over the melting pots should be provided, embracing also (by branch ducts if necessary) the receptacles into which the lead ashes are thrown. In mixing and pasting, the danger is from dust of oxides of lead to be controlled (see Fig. 6) by—(1) Exhaust ventilation by branch ducts protecting (a) the barrel from which the material is scooped, (b) the mechanical mixer into which the weighed quantity of oxide is discharged, (c) the bench at which the mixing by hand is done; (2) dampness of benches and floor to prevent raising of dust either by manipulation of the (often) heavy plates or trampling into powder the paste which may fall on the ground.

In assembling or putting together of the formed plates, and in earlier stages of the manufacture also, filing or use of a wire brush causes production of metallic lead dust and of the oxides when the brush touches them—a danger only to be met by exhaust ventilation. How far the poisoning to which the lead burners engaged in assembling plates is attributable to lead fume, produced by the high temperature of the blowpipe flame, and how far to handling (with inevitable dislodgment of dust) has not been satisfactorily settled. Incidence of poisoning on this class of worker in the past has been marked.

Generally there is need for impervious floors, solidly built, so as to prevent vibration and the raising of dust from passage of trolleys conveying the heavy plates. Gloves are frequently provided, more to protect the hands from contact with the sulphuric acid used in making the paste and jagged edges of the plates than as a preventive of lead absorption.

In the 10 years 1900-1909 incidence, according to precise occupation, has been—Casting, 33; pasting, 114; lead burning, 69; and assembling the plates, etc., 69.

Glass-Cutting.

[31]—Red lead enters largely into the mixture of raw materials for the manufacture of glass. Flint glass, for instance, contains 43 per cent. of lead. The raw materials (white sand, red lead, and generally saltpetre) require to be very carefully mixed, and a few cases of poisoning have been reported from the dust raised in sieving. One man works the sieve, resting on two runners across the bin, while another shovels the mixture into the sieve. The operation is not a continuous one, and respirators have principally been relied on to protect the workers. It should be possible to carry out the mixing operations in a dust-tight closed apparatus.

Poisoning from lead fumes generated in a glass furnace is unknown. Lead poisoning used to be common in the process of polishing cut glass on a brush by means of “putty powder” (oxide of tin, 29 per cent.; and oxide of lead, 71 per cent.), mixed with water to the consistency of a paste. The brush was made to revolve at high speed, with dissemination of the putty powder as a fine spray into the atmosphere of the workroom. Although rouge and oxide of iron have replaced putty powder to some extent—especially for the polishing of the bevelled edges of plate glass—no substitute can at present be found to give the final lustre and brilliancy required in the case of cut glass and in certain kinds of high-class work, such as polishing lenses.

Locally applied exhaust ventilation has robbed the process of its dangers. Pyramidal-shaped hoods enclose the spindle and putty box and brush before which the workman sits. The draught of the fan prevents escape of spray. The lad who feeds the brush with putty powder stands at the side, and in our experience his cap and clothes are now free from signs of splashing. Formerly the polishing was done by each man at his own berth, thus endangering the health of all working in the vicinity, as the custom of the trade is that the same man carries through the work both of cutting and polishing. Polishing occupies only about a fifth of a man’s time, and it has now, owing to the position of the fan, to be carried out in one particular part of the room.

In this small industry in the past the poisoning must have been considerable. In 1898 nineteen cases were reported. Reference to the table on p. 47 shows that the number now is greatly reduced. Those reported are generally cases which have ended fatally from the sequelæ of lead poisoning contracted many years previously.

Stained-glass painting—a form of vitreous enamelling—very rarely gives rise to poisoning, as no dust is generated (see vitreous enamelling for use of aerograph in glass-painting).

Paints and Colours.

[33]—Most of the cases have occurred in the manufacture of white-lead paint, although manufacture of chromate of lead and of Brunswick greens (barytes with which Prussian blue and chrome yellows are mixed) account for several. The following table shows the precise occupation of persons affected, the number of cases distributed according to precise occupation, and the proportion of these to the total in 225 cases which were closely examined:

Knowing the conditions of work, we can confidently assert that the poison must have entered the system in the form of dust in at least 90·0 per cent. of the cases, and in the remainder the possibility of dust having been the cause is not excluded.

In a small factory the cask of white lead is broken and the material scooped out into a pail. Scales are at hand, and when the amount of lead removed weighs half a hundredweight the contents of the pail are discharged either into a cylindrical pug-mill or into the pan of an edge-runner to be mixed with oil. In large factories the dry white lead is generally shovelled directly from the cask down openings or shoots in the floor to the grinding mills below.

Dangers and Prevention.

—Dust arises in unheading the casks from the displacement of air following the scooping or shovelling out of the lead, in filling the pails, and in discharging the lead into the mill. All points should, and can, be adequately protected by locally applied exhaust ventilation at each one of the points enumerated. A telescopic arrangement of the branch duct in connection with the barrel enables dust generated in scooping out to be removed as the contents of the barrel get lower and lower (see Fig. 15).

The lighter shades of yellow chrome are made by a cold precipitation process, or (as is usual for the deeper shades of chrome, orange, and red) by boiling the ingredients—lead acetate, pulp white lead, bichromate of potash and soda, and sulphate of soda—while barytes is added as the colour is being made. Danger in the first method does not arise (or only in minor degree when steam is injected to bring about more speedy solution) until drying and grinding (in edge-runners), sieving, and packing, are effected. The dust, when inhaled, is quickly absorbed, and in all these dry processes danger, in the absence of very carefully thought out exhaust ventilation, is great. In processes involving ebullition, danger is present in the steam which carries up with it chromate of lead in fine particulate state. Vats and vessels, therefore, in which the boiling is effected require partial hooding over and connection of the hood with an efficient exhaust. In subsequent wet processes of pressing the cakes of chromate of lead, the hands, arms, and overalls become thickly coated with pigment. Danger from chrome greens is practically limited to the dust created in dry grinding, usually effected in large edge-runners.

For references, see end of Chapter XVII.