Section 1, Requiring the Factory to Be Ventilated So As to Render

harmless, as far as practicable, all gases, vapours, dust, or other impurities, generated in the course of the manufacturing process, that may be injurious to health; of Section 74, empowering an inspector to require a fan or other means if this will minimize inhalation of injurious fumes or dust; of many regulations having as their principal object removal of dust and fumes; and of Section 75, prohibiting meals in rooms where lead or other poisonous substance is used, so as to give rise to dust or fumes. Unfortunately, owing to the difficulty hitherto of accurate collection, only a very few determinations of the actual amount of lead dust and fume present in the atmosphere breathed have been made. This lends peculiar value to a series of investigations by G. Elmhirst Duckering, which have thrown much light on the amount of lead fume present in the air of a tinning workshop, and the amount of lead dust in the air during certain pottery processes, and the process of sand-papering after painting. Incidentally, also, they help to determine the minimal daily dose of lead which will set up chronic lead poisoning. Aspirating the air at about the level of the worker’s mouth for varying periods of time, he determined the amount of lead in the fume, or in the dust, per 10 cubic metres of air, and from knowledge of the time during which inhalation took place he calculated the approximate quantity inhaled per worker daily. We have summarized some of his conclusions in the table on pp. 204, 205:

Duckering’s experiments as to the presence of fumes containing compounds of lead in the atmosphere breathed were carried out in a workshop for the tinning of iron hollow-ware with a mixture consisting of half lead and half tin. The process of manufacture and the main sources of lead contamination in the air (knowledge arrived at from these experiments) are explained on p. 59. As the result of laboratory experiments designed to show the effect of the violent escape of vapour produced below the surface of molten metal in causing contamination of the air, and the nature of the contaminating substances, he was able to conclude that the chemical action of the materials (acid and flux) used, and subsequent vaporization of the products of this action, was a much more important factor than the mechanical action of escaping vapour. Subsequently, experiments carried out on factory premises gave the results which are expressed in the table as to the relative danger, from lead, to (a) a tinner using an open bath; (b) a tinner working at a bath provided with a hood and exhaust by means of a furnace flue; and (c) the nature and extent of air contamination caused by the operation of wiping excess of metal (while still in a molten state) from the tinned article. In all three experiments aspiration of air was made slowly: it was maintained at the rate of 3 to 4 cubic feet an hour in the first experiment for between seven and eight hours; in the second for twenty-eight to twenty-nine hours; and in the third for twenty-four to twenty-five hours. The person engaged in tinning at the open bath was shown to be exposed to much more danger than one working at a hooded bath, while the wiper was exposed to even more danger than the tinner using an open bath, since not only was he inhaling fume from the hot article, but also fibre to which considerable quantities of metallic lead and tin adhered.

Analysis of samples of dust collected in different parts of the workroom bore out the conclusions derived from analysis of the fumes. Thus, samples collected from ledges at varying heights above the tinning bath containing the mixture of tin and lead contained percentages of soluble lead (lead chloride) in striking amount as compared with samples collected at points in the same room remote from any source of lead fume, while the insoluble lead present, as was to be expected from the fact that it consisted of lead attached to particles of tow floating in the air, was less variable.

TABLE XII., SHOWING QUANTITIES OF LEAD (PB) IN THE ATMOSPHERE AT BREATHING LEVEL.

(G. E. DUCKERING’S EXPERIMENTS.)

+------------------------------+-------------+--------+--------------+ | | | Esti- | | | | | mated | | | | Present |Time (in| Approximate | | | in 10 Cubic | Hours) | Quantities | | | Metres of | during | of Lead (Pb) | | | Air (Milli- | which | expressed in | | | grammes). | In- | Milligrammes | | +-----+-------+halation| inhaled | | |Total| Lead | took | by Worker | | Occupation. |Dust.| (Pb). | place. | per Day. | +------------------------------+-------------+--------+--------------+ | (1) | (2) | (3) | (4) | (5) | |Tinner using open bath | -- | 37·79| 5¹⁄₂ | 10·70 | | | | | | | | | | | | | |Tinner using bath covered by | -- | 6·36| 5¹⁄₂ | 1·80 | |hood, and having fumes | | | | | |exhausted by draught of | | | | | |furnace | | | | | |Wiping off (tinning) | -- | 124·31| 5¹⁄₂ | 35·20 | |furnace | | | | | |furnace | | | | | |furnace | | | | | |furnace | | | | | |Earthenware dipping (pottery) | 38 | 1·80| 7¹⁄₂ | 0·69 (average| | | | | |of 4 expts.) | |Earthenware dipping (pottery) | 84 | 6·27| 7¹⁄₂ | 2·40 (single | |furnace | | | |expt.) | |furnace | | | | | |China dipping (pottery) | 36 | 2·12| 7³⁄₄ | 0·83 (average| | | | | |of 4 expts.) | | | | | | | |Rockingham ware dipping | 44 | 2·26| 7¹⁄₂ | 0·86 (single | |(pottery) | | | | expt.) | | | | | | | | | | | | | | | | | | | |Earthenware cleaning (pottery)| 47 | 2·29| 7¹⁄₂ | 0·88 (average| | | | | |of 7 expts.) | |China ware cleaning (pottery) | 123 | 13·34| 6 | 4·08 (single | | | | | |expt.) | | | | | | | | | | | | | | | | | | | |Earthenware drying (pottery) | 25 | 2·19| 8 | 0·92 (average| | | | | |of 3 expts.) | |Earthenware glost placing | 34 | 2·08| 8³⁄₄ | 0·93 (average| |(pottery) | | | |of 3 expts.) | |China glost placing (pottery) | 30 | 1·08| 9 | 0·50 (single | | | | | |expt.) | |China glost placing (pottery) | 21 | 0·32| 9¹⁄₂ | 0·16 (single | | | | | |expt.) | |Majolica-painting of tiles | 61 | 9·11| 7¹⁄₂ | 3·48 (single | |(pottery) | | | |expt.) | | | | | | | | | | | | | | | | | | | | |{206 | 53·70| -- | -- | |Sand-papering and dusting |{ | | | | |railway coaches |{241 | 116·10| -- | -- | | |{ | | | | | |{ | | | | | {| 453 | 83·10| -- | -- | |Sand-papering {| | | | | |coach wheels {|1343 |1025·60| -- | -- | | {| | | | | |Sand-papering motor-car body | 600 | 278·30| -- | -- | | | | | | | | | | | | | | | | | | | | |{ 88 | 38·70| -- | -- | | |{ | | | | |Sand-papering |{ | | | | |motor-car wheels |{ | | | | | |{ 35 | 4·70| -- | -- | | |{ | | | | |Sand-papering van wheel | 494 | 143·80| -- | -- | | | | | | | | | | | | | | | | | | | |Burning off old paint | 52 | 3·40| -- | -- | | | | | | | +------------------------------+-------------+--------+--------------+

+-----------------------------+-----+--------------------------------+ | | | | | | | | | | | | | | Per-| | | |cent-| | | | age | | | | of | | | | Lead| | | | in | | | Occupation. |Dust.| Remarks. | +-----------------------------+-----+--------------------------------+ | (1) | (6) | (7) | |Tinner using open bath | -- |The whole inhaled in the form of| | | |vapour of lead or similar | | | |compound. | |Tinner using bath covered by | -- |The whole inhaled in the form of| |hood, and having fumes | |vapour of lead or similar | |exhausted by draught of | |compound. | |furnace | | | |Wiping off (tinning) | -- |14·1 milligrammes of metallic | |furnace | |lead inhaled as lead chloride, | |furnace | |and 21·1 milligrammes as | |furnace | |metallic lead adhering to | |furnace | |floating fibres of tow. | |Earthenware dipping (pottery)| 8·30|Dipping boards not used. | | | | | |Earthenware dipping (pottery)| 7·42|Very dirty dipping boards used. | |furnace | |Work very rapid, and much | |furnace | |shaking of ware after dipping. | |China dipping (pottery) | 5·43|China glaze usually contains | | | |about two-thirds as much lead as| | | |that of earthenware. | |Rockingham ware dipping | 4·37|Dirty dipping boards in use. | |(pottery) | |Glaze contains three times as | | | |much lead as ordinary earthen- | | | |ware glaze, but the ware is not | | | |shaken after dipping. | |Earthenware cleaning | 5·90|Cleaning done in or at front of | |(pottery) | |exhaust hood. | |China ware cleaning (pottery)|10·85|Very defective exhaust; hood so | | | |arranged that cleaning had to be| | | |done outside. Glaze contains | | | |about two-thirds as much lead as| | | |that for earthenware. | |Earthenware drying (pottery) | 8·58|Filter placed at breathing level| | | |in centre of drying stillage. | |Earthenware glost placing | 6·58| | |(pottery) | | | |China glost placing (pottery)| 3·64|Boards used were fairly dirty. | | | | | |China glost placing (pottery)| 1·50|One man only working. | | | | | |Majolica-painting of tiles |15·00|Tiles cleaned, while still damp,| |(pottery) | |with knife. Much dry waste glaze| | | |on wooden floor, and much | | | |traffic. Several cases of lead | | | |poisoning in this room. | | |26·10|Passenger fish truck after one | |Sand-papering and dusting | |coat of lead colour. | |railway coaches |48·10|Railway coach after one coat of | | | |lead colour on filled and faced | | | |surface. | | {|18·30|After two coats of quick-drying | |Sand-papering {| |white lead paint. | |coach wheels {|76·40|Old cream-painted wheel before | | {| |repainting. | |Sand-papering motor-car body |46·40|Door of motor body after one | | | |coat of lead colour and quick- | | | |drying sand-paper stopping. | | | |Urgent work. | | |44·00|Wooden motor wheels after two | | | |coats of lead colour and sand- | |Sand-papering | |papering between. Exhaust not | |motor-car wheels | |running. | | |13·30|Same point, but with exhaust | | | |running. | |Sand-papering van wheel |29·10|After one coat of quick-drying | | | |permanent red on two coats of | | | |flesh colour (sand-papering | | | |after each coat). | |Burning off old paint | 6·50|White paint of London and North-| | | |Western coach. Gas-burner used. | +-----------------------------+-----+--------------------------------+

=Dust.=--Reference to the table shows that the conditions in the pottery workrooms, as stated in Column 7, are reflected in Columns 3 and 5. Further details from his experiments may be useful. Thus, in a dipping room where low-solubility glaze was in use, the amount of lead in the dust collected per 10 cubic metres of air was 0·70 milligramme. The average of four experiments where there were no dipping boards was 1·80 milligrammes, and where dipping boards were used, 3·75; i.e., 1·95 milligrammes of lead in the dust per 10 cubic metres of air is added by the use of dirty dipping boards. As the result of his experiments, Duckering believes that approximately 1·95 milligrammes of lead per 10 cubic metres of air was due to the fine spray given off in the shaking of the ware. In bright sunlight, he says, the spray can be seen dancing high above the dipping tub. In a dipping house where work was done slowly by two occupants only, the proportion of lead in the measured quantity of air was also low--0·58 milligramme per 10 cubic metres. Where, in the absence of special provision made for admission of fresh air to a fan, the air was drawn from a neighbouring room in which lead processes were carried on, the amount of lead rose to 5·76 milligrammes at the level breathed by the gatherer at a mangle. In ware-cleaning the average of all his observations where lead was used (eleven) was 3·44 milligrammes; and he concluded that “wet cleaning of ware causes less direct contamination of the atmosphere, even where no local exhaust is applied. A still more important result of wet cleaning, however, is that the overalls keep much freer of dust.” The highest results were obtained when the process of ware-cleaning was done outside the influence of the exhaust draught. In one instance, where the ware was cleaned at a distance of 6 feet from the exhaust opening, 13·34 milligrammes per 10 cubic metres of air were found. Subsequently at the same point, after the exhaust system of ventilation had been remodelled, 0·95 milligramme only was present. Even in a stillage room in which no work was done other than the placing on and removal of the boards from the racks, the lead content per 10 cubic metres of the air was 1·08 milligrammes. In glost-placing, the average of four experiments was 1·83 milligrammes--no doubt the result of glaze on the boards. As much as 9·11 milligrammes of lead was found per 10 cubic metres of air in the centre of a large majolica-painting room, with wooden floors and much traffic in it. Wooden floors generally appeared to influence the results, as determinations of the lead present were higher in rooms with them than with tiled floors.

In coach-painting the proportion of lead found by Duckering in the air breathed during the actual time of sand-papering explains the severe incidence of poisoning in this class of work. The table shows the amount of lead in the air to be enormous, and in many cases much in excess of the amount found in the air when wiping off in the tinning of hollow-ware. The work of sand-papering is, however, very rarely continuous, the time occupied in it being, for the painter, about one to two hours daily; for the brush hand, two to three and a half hours; and for the painter’s labourer, four to five hours.

Knowing intimately the processes at which the estimations recorded in the table were made, the relative frequency of cases of plumbism reported among those employed at them, and the duration of employment prior to attack, we believe that, if the amount of lead present in the air breathed contains less than 5 milligrammes per 10 cubic metres of air, cases of encephalopathy and paralysis would never, and cases of colic very rarely, occur. And this figure is a quite practical one in any process amenable to locally-applied exhaust ventilation. Somewhere about 2 milligrammes, or 0·002 gramme, of lead we regard as the lowest daily dose which, inhaled as fume or dust in the air, may, in the course of years, set up chronic plumbism.

=Local Exhaust Ventilation.=--In considering preventive measures against lead poisoning, precedence must be given to removal of fumes and dust by locally-applied exhaust ventilation, as, unfortunately, the wearing of a respirator is neither in itself a sufficient protection, nor, if it were, could the constant wearing of one be enforced. A respirator is of no use against lead fume. In the case of dust, the conditions which it must fulfil to be effective are, first, that the air breathed is freed from dust, and, secondly, that it should not incommode the wearer. Further, it should be simple in construction, easily applied, and allow of frequent renewal of the filtering medium. No existing respirator of moderate price conforms quite satisfactorily with these requirements. The more closely to the face it is made to fit, and the more effectually the air is filtered, the greater is the inconvenience experienced when it is worn. This inconvenience is due to the exertion (showing itself in increase of the respiratory movements and pulse-rate) caused in aspirating the air through the filtering medium, and rebreathing some portion of the expired breath, containing a much greater proportion of carbonic acid gas and of moisture at a higher temperature than are present in fresh air. Respirators, therefore, except for work lasting a short time--half an hour to an hour--cannot be considered an effective or sufficient means of protecting the worker against dust. If a respirator must be worn, the simplest form is a pad of ordinary non-absorbent cotton-wool (absorbent wool quickly becomes sodden and impervious), about 3 inches by 4 inches, placed over the mouth and nostrils, and kept in position by elastic bands passed round the ears. The pad should be burnt after use.

With a smooth, impervious floor, however, and ventilation designed to remove the fumes and dust at, or as near as possible to, the point of origin, lead poisoning would become very rare in most of the industries to be described. The essential points of such a system are--(1) The draught or current of air set in motion either by heat or by a fan; (2) the ducts along which the current travels; (3) the hoods or air-guides designed to intercept and catch the fumes and dust at the point of generation; (4) inlets from the outside air into the room to replace continuously the air extracted, and, in many cases, (5) a suitable dust filter or collector.

Exhaust by Heat.--Processes giving rise to fumes or to dust liberated on stirring or skimming, which can be dealt with by the draught created in the furnace flue or over a bath of molten metal provided with adequate hood and duct up which the heated air travels, are--Smelting, refining, spelter manufacture, and the numerous operations necessitating the melting of lead, such as tinning with a mixture of tin and lead, sheet lead and lead piping, stereo pots in letterpress printing, pattern-making, tempering springs, file-hardening, etc. The dusting of red-hot metallic surfaces, as in vitreous enamelling, might possibly also be dealt with in the same way. The disadvantage of the exhaust by heat is the uncertainty and inequality of the draught, and the size of the duct necessary to cope with the volume of rarefied air from above the molten vessel.

The closer the hood is brought down over the point where the fumes escape, the less risk is there of cross-currents deflecting them into the workroom. Hence all baths of molten metal should have the sides and back closed in, leaving as small a space open in front as is practicable in view of necessary skimming or other operations.

In the case of tinning baths, Duckering describes completely successful results when from the top of the hood a shaft at least 24 inches in diameter was carried vertically upwards into the open air to a height of 18 feet, and the top of the shaft fitted with a wind screen in the form of a very large cone, having its lower edge below the upper edge of the shaft, and its nearest point at least 8 inches from the top of the shaft. Smoke produced in large quantity at any point 6 inches outside the front of the hood was entirely drawn into it. As, however, the inrush of air caused an eddy of the fumes at the upper edge of the opening, the edges of the hood were turned inwards, so that the operation of wiping was done in a sort of short tunnel. In general, it may be said that the diameter of pipes leading from hoods to the outer air (on the efficacy of the draught in which success depends) is much too small. Frequently mere increase in size will convert an indifferent draught into a good one. The height of the hood also--i.e., the distance between its lower border and the point where it joints the duct--is of importance. The shorter this distance is, the less serviceable does it become for the removal of fume. Indeed, it may even retain the fume which, were the hood not present, would rise to the roof. Sometimes safety is increased by making the hood double, leaving a space between the two sheets, and so concentrating the draught at the centre and at the margin. With a fan, ducts of less diameter can be used than when dependence is placed on heat alone. A duct carried into a chimney-stack has the advantage of dispersing the fume at a safe distance from the workroom.

The variableness of the draught produced by heat makes it unsuitable for removal of dust, except such as arises from skimming. The receptacle for the skimmings should always be kept inside the canopy of the hood. We have, however, seen the dust given off in the heading of yarn dyed with chromate of lead successfully carried away under hoods connected up by branch ducts with the main chimney-stack.

Exhaust by Fans.--The draught for removal of dust, and frequently also of fumes, is produced by a fan, of which there are two types: (1) low-pressure volume fans and (2) high-pressure centrifugal fans. In the first the draught is created by the rotation of a wheel with inclined vanes, causing the air to be driven transversely through the wheel parallel to the axis of rotation (Fig. 1). During a revolution a portion of the air is cut off from one side of the wheel, and transferred through the wheel to the other. Such fans are light, run easily, and are cheap. They are of many forms, both with regard to the number of blades--from two to eight--and general manner in which they are arranged. Some closely resemble the screw-propeller of a ship, while others have blades turned over and fastened on an outer rim. Their main defect is inability to overcome any but slight resistance in the course of suction behind, as from constriction in, or friction along the sides of, the ducts and right-angled bends, or of outflow in front, as from wind-pressure. Under favourable conditions, however, and when carefully fitted, a volume fan will exhaust dust and fumes through a system of ducts several feet in length, as, for example, from mono and linotype machines and electro melting-pots in letterpress printing works. But, in order to avoid resistance from friction, the ducts have to be somewhat larger in diameter than when a centrifugal fan is used. With nine linotype machines connected up to a 14-inch propeller fan, the branch ducts should be about 4 inches in diameter, and the main duct 12 inches, increasing from 12 to 15 inches within 2 feet of the fan-box. The shorter and straighter the course of the duct to the propeller fan, the more efficiently it works. Wind-guards are necessary to overcome resistance from this source in front, but their position requires to be carefully considered, so as to prevent the screen itself crippling the outflow.

If gratings are also inserted in the same duct for general ventilation the number of machines must be decreased pro ratâ.

All fans require frequent cleaning, and in this respect propeller fans have the advantage over centrifugal, in that they are usually more accessible.

Centrifugal Fans.--Generally, in the removal of dust, a strong suction has to be set up in a system of narrow ducts by means of a centrifugal fan--i.e., a fan-wheel formed by a number of vanes attached to an axle mounted in a spiral-shaped casing--so that when the wheel rotates air is carried along by the vanes, and flies off tangentially into the space between the blades and the casing, and thence to the outlet (Fig. 2). The air inlet or junction of the fan with the exhaust duct is at the centre of the fan, an arrangement by which the kinetic energy created by the rapid motion of the air leads to increase of draught instead of being wasted in production of eddies in the surrounding spaces. They are made in many different patterns, according to the nature of the work to be done. Their advantage over the propeller type in the removal of dust lies in the fact that they overcome greater internal resistance, and a uniform high velocity in a complicated system of pipes can thus more easily be maintained.

Ducts.--The main duct should be of metal (steel, sheet-iron, or zinc); it should be circular in shape, have as straight and short a course as possible, and be tapered in such manner that the area of cross-section at any point shall equal the combined areas of all the branch pipes which have entered it at that point (Fig. 3). Proper dimensions must be studied in relation to the size of the fan and the work to be done. Wooden ducts, unless chosen for specific reasons, such as the presence of acid in the fumes to be removed, are very unsatisfactory, as it is difficult to maintain them in an air-tight condition or to make branch pipes enter with rounded junctions. Where several branch ducts enter a main duct, situation of the fan midway between them has advantage, not only in saving metal in piping, but also in causing the distance of the fan from the farthest branch duct to be only half what it would be were the fan placed at the end of the system (see Fig. 7, p. 217). Further, the sectional area of the two collecting ducts will be less than that of one main duct, and greater uniformity of flow thereby secured. Where the two ducts join up into the single duct of the fan, the bends must be easy; otherwise the draughts would collide and neutralize one another. Branch ducts, if they cannot be made tangential to a rounded curve, should enter the main duct at an angle of 30 degrees, as by so doing equalization of the draught at different openings is made fairly uniform. The very common defect of a right-angle joint diminishes the draught by nearly one-half. Branch ducts should never be made to enter a main duct on the outer side of a bend, because at this point the pressure of the current of air inside the duct is increased. They should join up on the inside of a bend, where the pressure is reduced.

Hoods and Air-Guides.--As the object of hoods is to concentrate the draught on the fumes or dust to be removed from the worker, position in regard to origin of the fumes or dust requires first consideration. The more restricted the opening consistent with unimpeded work, the more effective is the draught, and the less disturbed will it be by cross-currents in the workroom. Pendock lays it down as a useful principle that the area of the front opening into the hood should not be more than four times that of the exhaust throat--i.e., the point of junction of the hood and duct (Fig. 4). Not less important is it that the draught should operate below the breathing level. Preference as to the direction to be given to the exhaust current should be in the order named: (1) Downwards; (2) downwards and backwards combined; (3) backwards and upwards combined; and (4) upwards only. Use should be made, for the removal of the fumes or dust, of any initial current of hot air set up from a bath of molten metal or from a heated metallic surface, as in vitreous enamelling. Hence under such circumstances only (3) and (4) need be considered. Generally hoods applied err in having too wide an opening, or they are placed too far away from the source of danger. They require sometimes to be adjustable to suit different-sized articles. Care is necessary to see that, when a hood has been adjusted for large articles, it is readjusted for smaller-sized articles. The principle of ventilation downwards and backwards is recognized as right for grinding and polishing on a wheel, since the tangential current set up by the wheel in its rotation is utilized. Pug-mills in paint-works are perhaps best ventilated by applying the exhaust to a dome-shaped hood covering the posterior half of the mill. Edge-runners must be encased, with an exhaust pipe attached to the casing and sliding doors or shutters for introduction or removal of material (Fig. 5). A small negative pressure inside the casing is all that is necessary, so as to insure passage of air inwards and not outwards. Branch ducts must protect the casks out of which material is scooped, and the receptacle into which it is discharged. In scooping out dry colour from a barrel, it is unwise to attempt to remove the dust created at every displacement of air on removal of a scoopful by means of a hood suspended over the barrel. Instead, the last joint of the duct should be a telescopic one, so that it can be lowered into the barrel, and be kept at a distance of about 6 inches above the material. The air is thus drawn downwards into the barrel (Fig. 6).

Processes such as colour-dusting, aerographing, ware-cleaning, enamel-brushing, and the like, are best carried out at benches under hoods with glass tops. Air will enter from in front, and carry the dust or spray away into the exhaust duct placed at the back of the bench.

=Collection of Dust.=--Frequently no heed is paid to the collection of the dust. Sometimes a dust chamber is arranged to intercept it on the far side of the fan, or attempt is made to blow the dust into a tank of water. The fine dust of which we are speaking cannot be satisfactorily collected by either of these methods, nor even by a cyclone separator, so useful for the collection of many kinds of dust. In lead works generally, the dust removed by the fan is best collected in filter-bags made of some porous fabric. Various efficient filters constructed on these lines by Messrs. Henry Simon, Ltd.; Messrs. Beth and Co., Ltd.; and the Sturtevant Engineering Company, Ltd., are on the market.

In collecting the dust, care must be taken to provide an adequate outlet for the spent air, so as to prevent creation of a source of friction in front which might destroy the effectiveness of the installation.

P, Patent “pentarcomb” for equalizing exhaust; V, patent “pentarcomb” for general ventilation; D, main and branch ducts; F, fan; U, upcast from fan; M, hoods over metal-pots of monotype machines, constructed to raise and lower, and swing out and in with metal-pot; L, hoods over metal-pots of linotype machines, constructed to raise and lower.

In the illustration “pentarcomb” grids connect the branch ducts over the metal-pots of mono and linotype machines with the main duct. The “pentarcomb” grids are arranged also elsewhere in the main duct itself to assist in the general ventilation of the workroom. The hoods over the metal-pots are constructed to be raised and lowered, and to swing out and in radially with the melting-pot arm. (Drawings supplied by the Zephyr Ventilating Company, Bristol.)]

In order to secure equality of flow from a number of branched ducts, the Zephyr Ventilating Company apply a special grating of curved and slanting inlets--the “pentarcomb”--to each branch duct. The air passing through the comb is split up into numerous small columns, and the inclination of the curve which each is made to take is such as to reduce friction to a minimum. By means of this device we have found, in a trunk with twenty branches, the draught at the one farthest from the fan as serviceable as that next to it. The method is illustrated applied locally to remove the fumes from linotype machines, and generally in the main duct for removal of foul air near the ceiling.

Where electricity is available as a motive power for driving the fan, some modification in the views expressed as to the curvature of the pipes and system of installation can be allowed. In a red lead plant, for instance, it may be desirable to have the pipes leading to the sifter or packing machine with sharp angles, so as to prevent tendency of such heavy dust to collect in them. The electric current allows a fan to be installed at any point desired; and if applied with knowledge that the increased friction due to an acute angle has to be overcome, the result may be quite satisfactory.

The various forms of vacuum cleaning apparatus with mouthpieces designed to aspirate the dust from different surfaces are sure to be increasingly used. In our opinion, wherever electric power is available, they will obviate barbarous methods involving use of hand-brushes to collect dust from machines, such as those for litho-dusting or for sweeping lead dust from benches and floors, or use of bellows to blow out the dust from compositors’ cases.

Finally, the carrying out of lead processes by automatic methods and with the interior of the casing under a negative pressure, so that the material is transported from one process to another by means of worms or conveyors, is everywhere to be aimed at. Or, again, it has been found possible on a commercial scale, by means of compressed air in a closed system of receivers and pipes, to force material in very fine state of division from one place to another, as, for instance, of litharge from the cask into the mixing machine for preparation of the paste for manufacture of accumulator plates, without risk of contact.

Indication of the efficiency of the draught may be gained by holding smoke-paper at the orifice of the hood. The definition of efficient exhaust in some regulations for the removal of fumes, as in the Tinning Regulations, is that it shall not be deemed to be efficient unless it removes smoke generated at the point where the fume originates. Accurate gauging, however, of the draught can only be done with an anemometer, so as to determine the number of linear and cubic feet passing through the throat per minute. Only rarely does one find an occupier alive to the value of the use of such an instrument. The importance of this point has been recognized in the Regulations for Heading of Yarn, by the requirement that the speed of each exhaust opening shall be determined once in every three months at least, and recorded in the general register. We prefer to use Davis’s self-timing anemometer, which gives readings in feet per second without the need of a watch. Other useful anemometers--Casella’s or Negretti and Zambra’s--require to be timed.

It is not available for velocities exceeding 1,200 linear feet per minute.

The details of all routine observations on localized exhaust ventilation might well be entered on a card hung up in the workroom. Such a card drawn up by our colleagues, Miss Lovibond and Mr. C. R. Pendock, has the following headings:

FIRM............................... PROCESS...........................

FANS: No..... Kind................ Size....... Maker................. Motive power........ H.P........ Method of driving..... Other load.......... Condition of driving.. Screen.............. Dust col- Direction........... lection.... Periodic cleaning...

HOODS: No..... Kind................ Size....... Structure........... Distance between each..

DUCTS: No..... Kind................ Size................ Length..... Section............... Structure........... Periodic cleaning...

FRESH-AIR INLETS: No.... Kind................ Position............ Size................ Fixed or temporary..

+-------+--------+--------------------+-------+------------+---------+ | Hood: |Position|Date................|Date................| | | Refer-| of | | | | | ence | Anemo- |External |External | | |Number.| meter. |Conditions..........|Conditions..........|Remarks. | +-------+--------+-------+-----+------+-------+-----+------+---------+ | | | |Speed|Volume| |Speed|Volume| | | | |Area of| F. | C.F. |Area of| F. | C.F. | | | | |Throat.| p.m.| p.m. |Throat.| p.m.| p.m. | | +-------+--------+-------+-----+------+-------+-----+------+---------+ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +-------+--------+-------+-----+------+-------+-----+------+---------+

Frequent cleaning and inspection of exhaust installations are very important, as accumulation of dust greatly impedes the flow of air at all points of the system. The person employed in cleaning the fan should wear a respirator. Hoods and ducts should always be cleaned with the exhaust in full action.

REFERENCES.

Annual Report of the Chief Inspector of Factories for 1910, p. 172.

Ibid., pp. 172, 173.

G. ELMHIRST DUCKERING: A Report on an Experimental Investigation into the Conditions of Work in Tinning Workshops, and Appendices. Included in Special Report on Dangerous or Injurious Processes in the Coating of Metal with Lead or a Mixture of Lead and Tin. Cd. 3793. Wyman and Sons, Ltd. Price 1s.

G. ELMHIRST DUCKERING: The Cause of Lead Poisoning in the Tinning of Metals. Journal of Hygiene, vol. viii., pp. 474-503, 1908.

G. ELMHIRST DUCKERING: Report on an Investigation of the Air of Workplaces in Potteries. Included as Appendix XLIX. in Report of the Departmental Committee appointed to inquire into the Dangers attendant on the Use of Lead, and the Danger or Injury to Health arising from Dust and Other Causes in the Manufacture of Earthenware and China, vol. ii., pp. 93-113, 1910. Cd. 5278. Price 1s. 9d.

G. ELMHIRST DUCKERING: Annual Report of the Chief Inspector of Factories for 1910, p. 47.

C. R. PENDOCK (one of H.M. Inspectors of Factories): Report on Systems of Ventilation in Use in Potteries. Included as Appendix XLVIII. in vol. ii. of Potteries Committee’s Report referred to under.

C. R. PENDOCK: Second Report of the Departmental Committee appointed to inquire into the Ventilation of Factories and Workshops, part i., and especially part ii., 1907. Cd. 3552 and 3553. Price together, 4s. 8d.

Other works referred to include--Construction des Usines au Point de Vue de l’Hygiène, by Ingénieur-Architecte Maniguet. Ch. Béranger, Paris, 1906; Hygiène Industrielle, by MM. Leclerc de Pulligny, Boulin, and others. J. B. Baillière et Fils, Paris, 1908; and many excellently illustrated trade catalogues issued by ventilating engineering firms, such as the Sturtevant Engineering Company, Ltd., London; Henry Simon, Ltd., Manchester; Davidson and Company, Ltd., Belfast; John Gibbs and Son, Liverpool.