Dangers and Prevention.
—The risk from dust in general labouring work, in depositing the ores in bins, in removing them to, and charging them into, the furnace, can only be controlled by watering, preferably by a spray. From the blast furnace lead fume and carbon monoxide may escape at the point where charging is done, if there is back pressure from blockage in the flues, or if the furnace blast is not working perfectly. In tapping the lead and in manipulations such as charging, drossing, and skimming, conducted through the doors of furnaces of all descriptions, hoods, extending at the sides down to the floor level, require to be arranged over the working doors, and connected either with ducts passing vertically through the roof or directly with the exhaust created in the furnace or flue itself. Dross and skimmings removed through the working doors should be received into iron trolleys capable of being covered, and not be allowed to fall on to the floors, to be shovelled up later on to barrows. Before such dross or slag from reverberatory furnaces is broken up for further treatment it should be well watered.
Lead absorption among the men actually employed in the Pattinson and Parkes’s processes is comparatively rare, as the temperature of the molten metal does not exceed 450° to 500° C. When, however, the zinc-silver-lead and gold alloy is removed for treatment in special furnaces for distillation off of the zinc, prior to cupellation, the lead from the Parkes’s pot, now free from silver, but containing traces of zinc, antimony, and other impurities, is run in some works into what are termed “market pots” for a final refining. Air and steam are blown through to oxidize the impurities. The pot is skimmed twice, the first dross containing antimony, etc., and the second a fine dust consisting of lead (60 per cent.) and zinc. The risk of poisoning at this point is considerable, although an exhaust fan connects up the cover of the pot with a cyclone separator, to carry away the fume when the steam is blown through. In other works this dezincing is done in a refining furnace, the material being then in a slaggy state, thus hindering development of fumes. After the condensation of the zinc in the distillation of the silver-lead and zinc crust the cover of the pot is raised, and the remaining metal, containing 80 per cent. of lead at a temperature of about 2,000° F., is ladled out into moulds for treatment in the cupelling furnace. The temperature at which this ladling operation has to be done makes the work impossible for those unaccustomed to it. Exhaust ventilation in the operation of emptying the pot, and cutting off the heat by a water-cooled jacket, suggest themselves as means to combat the undoubted risk.
In cupellation the temperature is high (about 2,000° C.), and fume will escape from the working door and from the opening where the rich lead is fed into the furnace. The danger here is sufficiently recognized by hoods and ducts placed in front of the furnace, but the draught, unless the ducts are connected up with a high-pressure fan, may prove inadequate to carry away all the fume.
Flue-cleaning, carried out usually at quarterly or half-yearly periods, is dusty work, as much of the dust is in so fine a state of division as to repel contact with water.
Smelting of other metals when the ores contain appreciable amounts of lead is equally productive of plumbism. Thus, in the year 1901 fourteen cases were reported from an iron works for the manufacture of spiegeleisen, the ore (now no longer used) coming from Greece[2]. In previous years it would appear to have been even greater. A remarkable feature of all the reported cases from this factory was that the form assumed was colic, and never paralysis. The poisoning was due to vaporization of the molten lead by the very high temperature to which it was raised as the molten iron flowed out of the furnace on tapping. The danger from fume was limited to the first few feet of the channel, as the heavier molten lead gravitated down between loose brickwork into a pit. Dust collected above the point where the furnace was tapped contained 39·77 per cent. of lead monoxide, and the flue dust 4·22 per cent.[3]. A flannel respirator worn once only by one of the furnace men contained lead equal to 16 milligrammes of lead monoxide. In 1906 three cases were reported in the extraction of copper. The persons affected were employed in charging ore into the cupola[4].
Heavy incidence of poisoning (twelve cases in two months) in a smelting works (now closed) led to examination of sixteen men. The gums of only one man were free of a blue line—in most it was particularly dense—eight were anæmic, one had paralysis of the wrists, and five others weakness. Analysis of the air was made at different points in the factory by the chemist of the works, G. D. Cowan, with the following results:
The samples from the cupola were taken from inside the hood (about 5 feet above the men’s heads). The gas was filtered through cotton-wool, so that all solid particles were retained, and the remaining gas was treated separately. The solid particles will be called “dust,” and the gas, after filtration, “fume.”
The cupola samples on being examined gave—
| Dust, | first sample | 0·08152 | grain of | lead per | cubic foot. | ||
| „ | second sample | 0·07297 | „ | „ | „ | ||
| Fume, | first sample | - | 0·00526 | „ | „ | „ | |
| „ | second sample | ||||||