Chapter XVI: Electric Generating Works

This article is simply an attempt to apply expert knowledge to the practical purpose of safe-guarding those employed in electrical works. The writer was a member of the Home Office Committee on Dangerous Trades, and of necessity much that now appears is a repetition of what was presented by that Committee in its Second Interim Report in 1897. It is satisfactory to record that many of the suggestions offered by the Committee have been accepted without hesitation and acted upon.

The generation and distribution of electrical energy, so far as it relates to the health and safety of the workers, may be considered under the following heads:--

(_a_) The risk of shock by accidentally coming in contact with conductors at high pressure, whether in generating or transformer stations.

(_b_) The fencing of all mill-gearing and machinery used for the conversion of mechanical into electrical energy.

(_c_) The health of the operatives.

Before dealing with these specific points it may be desirable to state in general terms what is meant by “generating and transformer stations.” A generating station is a place in which, by the aid of steam, gas, water, or other source of power, mechanism is used for driving dynamos, which are machines for converting mechanical into electrical energy, whether for producing light, driving machinery, running railways, tramcars; for depositing metals, plating, welding, heating, etc., etc., or for charging storage batteries.

Transformer stations vary in size from buildings of considerable proportions to mere cellars, or even boxes too small for entry. In such places are found appliances for the conversion of small current at high pressure to large current at low pressure, or _vice versâ_. Stationary transformers are used for alternating currents, while rotary converters or transformers, requiring more room and attention, are necessary for direct currents.

To appreciate the risks hereafter described, a statement in the most elementary terms now follows, showing how mechanism can produce the foregoing results.

A conductor of electricity, _e.g._, a piece of copper wire made to traverse a magnetic field (that is, the space between the poles of a magnet), has an electro-motive force, or difference of electric pressure, set up in its ends, which depends upon its length in the field, its velocity, and the strength of the field, being in fact proportionate to the product of these three. As the movement cannot continue in a limited field in one direction indefinitely, it must be reversed, thus causing a reversal in the electrical state of the ends. If the ends slide on stationary conductors, these too will share the electrical state of the ends, and alternating current will pass between these stationary conductors if they are joined by a conducting wire. This current will be greater as the difference of pressure is greater and as the electrical resistance of the conducting circuit is less. In order to increase the effect of a moving conductor, its length may be increased by suitable windings, the arrangement of which, however, cannot be described in these pages. The effectiveness, moreover, is enormously increased by winding over a laminated iron core, which greatly increases the magnetic force. If, instead of connecting the ends to sliding contact rings from which an alternating current is taken off by stationary contact brushes, the ends of a number of coils are joined to a series of insulated commutator bars, it is possible by suitable connections so to arrange that all the coils remain in action and that the points of the commutator rubbed by the fixed conducting brushes do not change in their electrical pressure, so that a direct (_i.e._, non-alternating) current is the result. This is desirable for arc lighting, and is essential for charging batteries and generally for effecting chemical change.

Dynamos of many forms are made. Sometimes the field magnets revolve, the armature being stationary, but usually the reverse is the case. In some machines there are two poles only, in others, many. The main principle, however, is the same in all.

When the direction of the current is not commutated, it will, in consequence of the rapid revolution of the armature, alternate or change its direction very frequently, 100 alternations in a second being not uncommon. The currents produced may be classed as low pressure, high pressure, and extra high pressure. Currents at low pressure distributed from generating stations are invariably direct. High pressure currents are distributed either as direct or alternating. One, if not more, extra high pressure station in Great Britain supplies alternating current.

Opinions differ as to the pressure at which these currents become dangerous. The recommendation made by the Committee before referred to was to the effect that currents should be considered dangerous at 700 volts direct, and 350 alternating; and that all metal conductors carrying a current equal to or greater than this should be deemed to be at high pressure. It is from currents at high pressure that we may expect special danger to life from shocks caused by parts of the body coming in contact with conductors differing considerably in pressure, not necessarily metal conductors, for one contact may be with earth, especially if the ground is damp. American experts have laid down that the pressure which may be relied upon to cause death is 1500 volts. According to this standard, the Home Office Committee would appear to have erred on the side of extreme caution. Subsequent events, however, have proved that this is hardly the case. Possibilities fore-shadowed in section 19 of its report have almost literally been realised in a large factory at Bradford, where a lad, aged nineteen, engaged in doing repairs, came in contact with a frame of an arc lamp. He was working in a warm cellar, his boots were damp, and, unhappily, he stood upon an earthed metal plate. The frame of the lamp accidentally touched formed part of the circuit. A leakage from the positive brush to the dynamo-frame, which was earthed, created a short circuit between the frame of the dynamo and the frame of the lamp, the man forming a part of the circuit. A direct current, of 250 volts only, passed through his feet, probably through his heart, causing death. It is much to be regretted that artificial respiration, as recommended by eminent authorities and described in the report of the Committee, was not attempted. An article published in _Nature_ of 23rd August 1900, gives in detail a description of experiments carried out by Professor H. F. Weber, of the Zurich Polytechnic, to decide what pressure is dangerous on electric railways with overhead trolley wires. These experiments were undertaken owing to a dissension, between a firm of electrical engineers and the Baden authorities, as to the proper pressure to be used for two electric railways to be worked by the 3-phase alternating current. The details showing the physiological effects on the human body are highly interesting, Professor Weber allowing himself to be the medium of the experiments, and constituting himself the measuring instrument. Two series of experiments were made. In the first, a person seized the two bare leads with both hands simultaneously, or both of the leads fell upon a bare part of the human body. In the second, a bare part of a person standing on the railway, or on a car, came into contact with one of the leads. Professor Weber draws the following conclusions:--

“A simultaneous touching of both of the poles of an alternating
current circuit is dangerous as soon as the pressure exceeds 100
volts; and since it is impossible to set one’s self free, the
case must be regarded as fatal whenever immediate help is not at
hand.”

“These results,” continues the article, “are consistent with several disasters which have happened in practical life.

“In 1896, in Horgen (Switzerland), a man, to prevent himself falling from a ladder, seized with both his hands two non-insulated leads with a P.D. of 240 volts between them, and was immediately killed. In a mine in Silesia, a workman seized in the same manner some non-insulated leads and was killed, on account of his being unable to release them, the P.D. being 300 volts. In the Electric Central Station in Olten, a workman, desirous of proving to his companions that a pressure of 500 volts was quite safe, seized both of the leads and was killed instantly. From this it is obvious that the general opinion of a pressure of 500 volts not being dangerous does not hold good, the limit being much lower. In spite of the great number of disasters which have already happened, the danger does not seem to have been generally appreciated, and workmen and erectors are often seen to deal with leads and apparatus of relatively high pressures in the most careless manner. That disasters have not taken place oftener may be due to the fact that in most cases help has been readily at hand.”

In the second series of experiments the person is supposed to stand on one of the poles itself, namely, the earth, being rather well insulated by means of his shoes. In this case the conclusion arrived at is that--

“To touch one of the poles is not dangerous as long as the
pressure does not exceed about 1000 volts; the intense
stinging which appears at the first slight touching serves as
a protection against the danger, for the hand is instinctively
drawn back rapidly.

“The main result of these experiments is, then, that all
pressures between 100 and 1000 volts must be regarded as equally
dangerous, and consequently there is no reason for not using the
higher pressures between 500 and 1000 volts, especially as they
lead to greater economy in the working of the electric railway.
Further, there is only a very little chance of the passengers
or other persons coming into contact with both of the leads. To
this danger the employés only are exposed, and being generally
people with some electric training, they are acquainted with the
danger, and may be supposed to be sufficiently careful.”

It is of interest to note that the authorities, after the investigation, decided upon allowing a working pressure of 750 volts. Both series of experiments relate to alternating currents.

There is perhaps no better method of impressing upon people the dangers of electric shock than by stating briefly, as under, some of the fatal accidents that have happened during the last few years in electrical stations, factories, and other places in the United Kingdom. Fatalities in transformer stations will be separately noticed. The voltages in most cases were from 2000 to 2400; in one case 1000, and in another (a high pressure station) 10,000:--

1. Touching exposed terminals when manipulating a switch at a generating station.

2. Accidentally grasping an insufficiently protected volt meter wire.

3. When up a ladder in a central station, deceased accidentally came in contact with a highly charged metal conductor.

4. When oiling the bearing of an alternating machine, and using a metal can, the can came in contact with a highly charged conductor. Deceased had one hand on a metal rail intended for the protection of the machinery. The current passed through the metal can, through his body, and thence to earth.

5. When doing repairs at the back of a switch at a central station, deceased accidentally touched two metallic connections varying greatly in pressure.

6. When a workman was carrying an iron ladder in a factory the ladder touched a highly charged conductor in an arc lamp circuit, the current passing to earth through the body of deceased.

7. Whilst performing test operations at an electrical station.

8. An operative was putting some capping on a casing in an electric lighting works. Inadvertently he drove a screw through the insulation of a cable then “dead.” The current was turned on. The operative touched the screw head and at the same time an adjacent water-pipe. The current passed from the screw through his body and the water-pipe to earth. (A brother of this man was killed in a transformer chamber.)

9. An operative, when at work in a factory, accidentally stumbled, and seized hold of a wire stay supporting a pole of an arc lamp. There must have been a defect in the insulation, and this stay was highly charged, the man being killed instantaneously.

10. When covering wires leading to a switch, deceased fell across the terminals of one of the machines.

11. By accidentally touching a synchronising switch in a generating station when doing repairs. The current passed through deceased’s body to an iron column that he happened to be touching at the same time.

12. A boy employed in a large steel factory accidentally came in contact with the frame of an arc lamp lowered for the purpose of recarbonising.

13. An operative employed in ironworks accidentally touched a wire used for raising and lowering an electric arc lamp. He was found on his back in a weighing-cabin. Another workman thought that he was in a fit, and went to his assistance. Both men received fatal shocks.

14. At an extra high pressure generating station an operative was found dead on the floor. Medical evidence tended to show the difficulty of stating with certainty whether the man died from shock or from heart disease. The coroner’s jury, however, found that death was due to asphyxia produced by electric shock.

Our attention may now be turned to fatalities in transformer stations, or boxes in which alternating currents at high pressure are converted to large currents at low pressure. A dangerous pressure is found in the main conductors, this being reduced by causing induced current in the consumer’s circuit, the strength depending upon the proportion of the windings in the primary and the secondary circuits, the secondary being in no way metallically connected with the high pressure main. Under these circumstances, and under normal conditions, the safety of the consumer should be secured. That, unhappily, cannot be said so far as relates to the workers, whose duties take them near the transforming apparatus. It is undesirable to give names, places, or dates, but the following brief summary of fatal accidents that have happened during recent years in transformer stations may be relied upon as being generally accurate. Many non-fatal accidents have happened, but these are not noticed.

1. Attempting to assist a servant of an electrical company, who was working in a cellar on the consumer’s premises, and who received a severe but not fatal shock.

2. Killed when pulling back the slack of a main wire in a street surface-box.

3. Accidental contact with undischarged and unfenced omnibus bar in high pressure distributing station.

4. A second accident of the same kind as the last foregoing, and at the same station.

5. Killed when dusting a high pressure fuse in a cellar transformer.

6. Contact with dangerously placed terminals at a transformer chamber in a cellar.

7. Accidentally touching a high pressure terminal when cleaning or repairing in a street transformer chamber.

8. Touching a highly charged transformer frame in a street chamber. Defective insulation in the main conductor led to leakage and to the frame becoming highly charged.

9. When descending by an iron ladder to a street transformer chamber, the operative came in contact with a highly charged frame of a transformer.

10. Two workmen were removing a transformer from a corporation sub-station. They accidentally put on a wrong switch. The exposed ends of the cable, which were in contact with the transformer frame, caused the frame to become highly charged. Two men touching the frame were killed, others were seriously injured.

11. A workman, when making a connection in a corporation sub-station, came in contact with the bared ends of a highly charged cable.

12. Killed by grasping an imperfectly insulated connection in a street transformer pit.

Such accidents are not confined to operatives. The following are known to have been due to electric shock. At Bournemouth, ’bus horses outside a hotel fell down dead. At Norwich, dogs that passed a certain spot uttered an unearthly howl. At Hartlepool an overhead wire broke, killing a horse. Two cabmen who came to the rescue received severe shocks. The _Matin_ of 27th January 1897 describes how two horses were suddenly struck down by the current from a subterranean cable used for running an electrical tram. In Dublin a gentleman was standing close to an electric lamp in the street, which he states paralysed him, causing him to fall “like a lump of lead.” Others going to his assistance received shocks similar to those of the two cabmen at Hartlepool. The _Melbourne Argus_ records a fatality to a young man who climbed a pole supporting a heavily charged wire, which he touched. “This,” says the _Argus_, “is not the first terrible accident which has happened in connection with the lighting of the city and suburbs. At the Richmond works of the New Australian Electric Light Company, whose wires were concerned in Saturday’s fatality, a workman or overseer was killed instantaneously through touching a “live” wire. Another, who was engaged in the A. U. Alcock works in the city was more fortunate. He seized a wire with one hand to prevent himself from falling, and was so seriously shocked by the current that he could not let go. Another workman, observing his predicament, cut the wire, and he fell to the ground. A third and even more remarkable case than the others occurred some time ago in Russell Street. There had been a violent storm, and a post carrying electric lighting wires had been blown to the ground. In the fall some of the wires broke and trailed across the footway. A pedestrian idly picked up the end of one of the broken wires. In a moment he was kicking and plunging upon the ground, unable to release his hold of the wire. Another pedestrian, who saw the accident, and who recognised that it was a struggle with death, hastened to the rescue, and attempted with all his strength and both his hands to drag the first man into safety. His good heart cost him his life.”

Enough has been said to show that a shock, whether from a direct or an alternating current at high pressure, is highly dangerous to life, many authorities being of opinion that the alternating is the more deadly current of the two.

Where a direct current is transformed, it is done by mechanical appliances. The risks to operatives in such a case include those that are incurred where machinery is left unguarded; but in dealing with alternating currents no mechanism is used, and the risk is confined to the danger from shock. The cases quoted show, better than detailed explanations, the manner in which these shocks are received, and it cannot be out of place to urge the importance of insisting on all known precautionary measures for the protection of those whose duties take them into transformer stations. The number of such places increases year by year, and they are likely to increase to a greater extent in these days, when induction motors, driven by alternating currents, are so rapidly coming in favour for running machinery in factories. Modern science has shown that the alternating current can be used in this manner, and that by substituting the alternating for the direct current, power may be economically conveyed for considerable distances, the advantages of the alternating current being the ready conversion of high to low pressure, and hence the saving of copper in the conducting wires, the further saving of the cost of brushes and commutators, whilst the absence of “sparking” lessens the risk of fire, and the non-handling of brushes, etc., reduces the danger of shock. These advantages were referred to and summarised in the report of Mr Bremner Davis, reproduced in the Report of the Chief Inspector of Factories for the year 1898.

Science has not yet explained what is the mystic force known as “electricity.” Its effects, however, are known. How the human system is affected by contact with a conductor charged with electricity at high pressure has been fully considered by eminent scientific men, such as Drs D’Arsonval, Goelet, Hedley, and Lewis Jones, to whom the public are indebted for suggestions on which were based the excellent rules published by the _Electrical Review_, for dealing with apparent death from electric shock. A copy of these suggestions is appended, and one should be found and understood in all places where electricity is used.

The highly interesting question as to how death from electric shock is caused, is ably dealt with by Professor Thomas Oliver, who in an article published in the _British Medical Journal_ of 15th January 1898, placed the public in possession of knowledge gained by experiments and long and careful study. He believes that electricity kills either by suddenly arresting respiration, or by stopping the heart’s action. A series of experiments carried out by him showed that in most instances the effect of the electric shock was felt principally by the heart. This organ immediately ceased to beat where very high pressure currents were used, whilst breathing might continue a few minutes longer. Within the last few months, Drs Prevost and Battelli, of the Geneva University, have instituted a fresh series of experiments, and they have found that whether the direct or the alternating current is used, death comes, practically speaking, in the manner stated by Dr Oliver, viz., by paralysis of the heart. Dogs were in this way immediately killed, and yet the breathing continued for a few minutes afterwards. When fairly high voltages were employed, _e.g._ 550 volts, these experimenters found that the heart was suddenly arrested by one shock, and that, while the breathing was at the same time suspended for a few seconds, respiration gradually returned in a feeble and superficial manner, and soon finally ceased.

After all, the main question is, how to avoid death from electricity; and the obvious reply is, avoid shock. This is no simple matter, but to some extent a solution is found in the recommendations made by the Home Office Committee, which were largely based upon the opinions of Professor C. V. Boys (a member of the Committee), and other eminent electricians. These recommendations are here reproduced in appendix form. In the light, however, of fresh experience showing that an artisan working in a factory was killed by direct current at 250 volts, prudence may hereafter suggest that precautions should be taken in places where the voltage is lower than that named by the report.

The operatives engaged in electrical works do not appear to be subject to any exceptional risks so far as health is concerned; but those who work where plates for storage-batteries are manufactured, or who subsequently manipulate the plates, are liable to suffer from plumbism. Special Rules founded upon the recommendations of the Home Office Committee appointed in 1893, and known as the “White Lead Committee,” were issued by the Home Office. These apply to electric accumulator works, and require the provision of bath and lavatory accommodation, hot and cold water, soap, brushes, towels, respirators, and overall suits for persons employed in mixing dry red lead and dry litharge, and gloves and aprons for persons engaged in “rubbing,” that is, rubbing red lead into the interstices of the lead plates.

Rooms in which accumulator batteries are found are always well-ventilated, preventing any undue accumulation of oxygen and hydrogen gas given off during the charging process, but in electric launches or tramcars, where the accumulator cells are shut up in confined spaces, dangerous explosions have taken place.

So far as the fencing of machinery and mill-gearing used in the generation of electricity is concerned, common sense points to precautions being taken, such as are required in all factories. All dangerous mill-gearing, such as cranks and fly-wheels of engines, shafting, wheels, drums, pulleys, etc., for communicating the first moving power to the machines, should be securely fenced. In doing this, however, special care should be observed lest in removing one source of danger another may be created. In ordinary factories fencing-rails are almost universally of metal. These rails in generating stations should be of wood or other insulating material; for should, perchance, an operative make an accidental contact with metal at high pressure in the circuit, at the same time touching any part of a metal rail, the current would pass through his body to earth, always assuming that the rails are not sufficiently insulated from the earth. Such accidents have happened, and are liable to occur again, to men engaged in oiling bearings, adjusting brushes, cleaning commutators, collector-rings, etc., the risk of course being increased should any defect in insulation cause the current to run to frame. Terrible fatalities due to unfenced machinery have occurred in generating stations, as in other works, none more painful perhaps than one that happened to an engine-driver at an Electric Supply Company’s works, who, when examining bearings, fell into some part of the machinery driven by a 7000 horse-power engine, and was torn to pieces.

As time goes on, there appears to be a fuller realisation of the dangers incurred, and it is not too much to expect that those in positions of responsibility will heartily co-operate with public officials in taking precautions suggested by prudence and common sense.