Chapter XXIII: Basic Slag

In the manufacture of steel by the Thomas Gilchrist or basic process, there is a large percentage of waste product, which is known by the name of basic slag. This, notwithstanding its high percentage of phosphorus, remained for some years of little or no value, until it was found that its fertilising properties could be obtained by reducing it to an exceedingly fine powder. Since that was done, it has been in great demand as a manure. It is the manufacture of this manure which is said to produce deleterious effects upon the workmen engaged, and which has brought it within the meaning and regulations of a dangerous trade.

The composition of basic slag is:--

Lime 41.58 per cent.
Magnesia 6.14 „
Alumina 2.57 „
Peroxide of iron 8.54 „
Protoxide of iron 13.62 „
Protoxide of manganese 3.79 „
Protoxide of vanadium 1.29 „
Silica 7.38 „
Sulphur 0.23 „
Calcium 0.31 „
Sulphuric anhydride 0.12 „
Phosphoric acid 14.36 „

Before crushing, the slag is in large pieces, and it has to be ground into an almost impalpable powder, so that 80 to 85 per cent. of it will pass through a mesh of 10,000 to the square inch. There is still a more impalpable dust given off which, notwithstanding the utmost care, escapes from the machinery during the process of grinding.

The grinding is performed in several ways, sometimes by means of edge runners, sometimes by flint pebbles, and sometimes by means of heavy balls called the Krupp ball system. The following is a description of the process as carried on at the North Eastern Steel Works, Middlesborough.

The main building is of three storeys, the ground floor of which is used for the various pulleys and driving gear for the mill.

On the first floor are six roller mills, and on the top floor are ten Askam separators, three screens, and a main conveyor, into which each separator discharges the dust.

Outside the main building, but connected with it, on the ground floor, is a shed in which are placed four edge runner mills.

The slag is put into the first edge runner, and crushed until it is fine enough to pass through grids at the bottom of the mill, and it falls through these on to an elevator, which takes it up to the screen on the top floor. That which is not fine enough to pass through this screen falls down into the second edge runner, where it is ground in a similar manner and again elevated to the top floor.

After the slag has passed through the screen, it is taken into the first two separators, where the fine dust is taken out and falls into the main conveyor, and is carried by means of this direct to the warehouse.

The tailings from the separator fall into the roller mills on the first floor, where they are crushed up, after which they fall into the second edge runner mill, where they are ground and treated in exactly the same way as in the first edge runner mill. This process being repeated altogether four times, the slag is then found to be pulverised.

The dust made in the separators is conveyed direct to the warehouse, as above described; but that made by the roller mills on the first floor is drawn by means of a fan into a long tube, running the whole length of the building, and from this it passes into a long dust-tight chamber, called the stive room. The floor of this room is cleaned by scrapers, which take the dust into the main conveyor above referred to. The dust is finally received into a hopper, and from this it falls automatically into bags, in quantities of about a hundredweight.

In the early years of its manufacture, the process was conducted in such a way that it was undoubtedly a very dusty occupation, and the men working at it then suffered constantly from what they called the “slag cough.”

Some two or three years after its manufacture was begun, there was an outbreak of epidemic pneumonia in Middlesborough, and it was thought by many to be in some way caused by the new industry. As the disease (in 1888) assumed very serious proportions, it was thought expedient by the sanitary authority to invite the co-operation of the Local Government Board. Dr Ballard came down, and after a most careful inquiry, he reported that “the slag dust to which the epidemic had been attributed was not the cause of the pneumonia, but that when from any cause pneumonia becomes epidemic, persons largely exposed to the inhalation of this dust may and do suffer more than persons not so exposed, and that the disease with them is of high fatality.”

In 1893 the attention of the Secretary of State was again called to the injurious nature of the trade, and Mr Gould, Her Majesty’s Superintending Inspector of Factories, conducted the inquiry, and made a report in December of that year, in which he says:--“Being in its nature extremely fine, it has a tendency, when inhaled, to settle in the farthest ramifications of the air-passages, and to induce in the mucous membrane of these a chronic state of irritation, thus rendering the larynx and bronchial tubes unduly susceptible of further mischief should the subject take cold; and in general creating a distinct predisposition to bronchitis and pneumonia. Moreover, it is found that when pneumonia does supervene, a fatal result not unfrequently follows, with unusual rapidity. But even in a case of complete recovery from an acute attack, the patient will be constantly liable to a recurrence of the same malady, as his breathing apparatus is continually undergoing deterioration, so long as he is subject to the influence of the dust.”

The summaries of these two inquiries may be taken as representing all that could be said about the effects of slag dust at that time; and it remains for me to state whether more recent observations have tended to confirm these conclusions.

In investigating the subject, I have examined a number of men engaged in daily occupation at the mill, and I subjoin a short report of some of them.

S. R., 54, been in the mill twelve years; well nourished; no complaints except occasional cough after starting in the morning; breath sounds not very distinct at the base of the lungs, and expansion of chest rather deficient.

J. R., 32, worked in the mill thirteen years; chest expansion rather deficient; general health good; occasional cough.

E. F., 31, worked eleven years; good appetite and good health; had pneumonia fifteen years ago; does not suffer from colds, but coughs sometimes in the mornings.

W. J., 44, has worked nine years; always has cough, which is worst about an hour after leaving work; expansion of chest diminished.

J. T., 52, worked thirteen years; health equal to the average. Three years ago had pneumonia; ten weeks off; colds not common; respiratory murmur diminished over the bases of lungs; expansion lessened.

N. R., 44, worked eight years; health good, never ill; colds often.

In measuring the chest, it was found that there was only a difference of about one and a half inches between that of inspiration and expiration, showing considerable diminution in chest capacity.

With regard to the causation of chest affections there can be little doubt that it produces increased action of the bronchial mucous membrane, and consequent cough. But unless this is accompanied by such influences as wet, cold, exposure, or drink, there is no reason to think that it is the cause of acute bronchitis. Indeed, notwithstanding excessive carelessness in their habits, I should say that the tendency in the great majority of cases is towards a chronic affection of the bronchial tubes, followed after some years by emphysema.

The men nearly all suffer more or less from cough and some mucous expectoration, which makes them frequently seek relief from cough medicines. In the last few years, however, great improvements have taken place in the grinding mills, and the men now tell me that their discomforts are greatly reduced.

In the cases examined, there was accelerated breathing in three, and diminished power of expansion more or less in all of them.

It will be seen from the chemical analysis of the slag that there is nothing in it of the nature of a poison such as to produce immediate injurious consequences, beyond such effects as may be traced to its mechanical action upon the bronchial tubes and air cells. The phosphoric acid is in combination with the lime as a tetraphosphate, which is not corrosive, nor generally harmful. There is, however, a good deal of irritation produced in those unaccustomed to it, for on the last occasion when I visited the works, I felt some tightness in the chest, with cough and roughness of the voice, which lasted three or four hours.

Inquiries have failed to elicit that any undue proportion of slag-workers have been attacked by pneumonia. As the medical profession in Middlesborough had come to suspect pneumonia in slag-workers as infectious, with a view to helping in its investigation an arrangement was come to with the Health Department of the Town Council to have the cases of pneumonia notified. Of these, 36 were labourers, and the other 67 embraced nearly the whole catalogue of special workers and trades, such as crane men, gantry men, carters, trimmers, blacksmiths, joiners, fitters, and moulders, besides printers, barmen, publicans, butchers, teachers, and insurance agents.

During the latter half of 1900, Dr Dingle, the Medical Officer of Health, received 103 notifications of pneumonia in adult males, which he inquired into. After a very careful inquiry, Dr Dingle failed to fix any special degree of susceptibility upon any particular occupation. Slag dust does not play any prominent part in causing pneumonia.

In the treatment of the immediate effects of the inhalation of slag dust, the remedies for ordinary catarrhal conditions of the bronchial tubes answer as well as anything; and as its remote effects are in no way different from those produced by other dusty occupations, remedies which prove useful in those, such as potassium iodide, carbonate of ammonia, digitalis, and strychnine, have, in my hands, proved most efficacious.

But our efforts must be directed more to the prevention of the initial ailments, and to the amelioration of their causes than to their treatment by medicines, for it must not be forgotten that the tendency is always towards the production of structural changes in the tissues of the bronchi and lungs.

There is a standing order in all of the works that the men should wear respirators, and these are provided by their employers. But hitherto no form of respirator has been suggested which answers the necessary requirements of being porous and comfortable, and at the same time impervious to dust. The face bag, which was one of the results of Mr Gould’s inquiry, ought to be of great service; but it becomes saturated with the moisture of the expired air, the result being that during inspiration it is drawn up against the mouth and nose, and a sufficient quantity of air not being available, the workmen slip it down underneath the chin, where, of course, it is useless. No contrivance will ever answer the purpose which does not admit of easy access of air into the lungs, and of complete expiration without effort. For this purpose a light, soft wire mask might be made to fit the face, which should stand out from the mouth and nose. It should contain a shutter, by which several layers of open webbing could be enclosed, through which the breath could be easily drawn; and there should be an opening fitted with a valve, which should open easily for outward, but shut for inward breathing.

The finished material is placed in packing bags, in the fitting of which the openings are tightly fixed round the hopper, and by means of a lever the charge is suddenly dropped into the bag, when a cloud of dust immediately rises. There is consequently more dust in this department than there ought to be, and, moreover, it is the finest dust of all, for it comes through bags of very closely-woven texture. If the packing material were dipped in size, or rendered impervious in some other way, this source of danger would be largely reduced.

There is another improvement which might be suggested, and that is, that the men should be provided with a room, outside the mill altogether, in which to take their meals. As it is at present, the grinding goes on without stoppage for meals, which renders it necessary for the men to be on hand the whole time; consequently there is no opportunity for open-air breathing time. By a little arrangement the men could probably go in batches, and have their dinner in comfort, and for a time be free from the atmosphere of the mill.

JOHN HEDLEY.