The Danger of High Voltage Wires in Fire Fighting
Streams in the Vicinity of Such Heavily Charged Wires Hazardous— Heavy Shocks Received Through Streams on Transformers
A QUESTION as to whether fatal electric shocks can be received by firemen through the medium of streams directed on heavy transmission and other electrical systems is one that has been debated pro and con many times and never definitely settled. Certain it is that heavy shocks of electricity can be transmitted by the agency of streams which are directed on heavily charged electrical lines. The part of safety is to avoid directing such streams upon or near any heavily charged wires. Mr. Stephen’s contribution to literature on this subject will be found of great interest and instructiveness.
Among other institutions fostered by the rapid advancement of modern invention there are few that have risen faster and extended further than the recent development of hydro-electric power. This could scarcely have taken place, nor could our present great electrical transmission systems exist, were it not for the fact that the power to light cities and turn wheels may be carried through copper wires over great distances and necessarily at differences of potential that range from approximately 20,000 to 100.000 volts.
Probably this subject does not seem related to that of fighting fire, but whenever one or more of these high tension transmission lines, on steel towers or high poles, enters or approaches the limits of a city the local fire chief has a new complication to consider.
Dangerous High Tension Lines
In most cases the high line feeds a sub-station near the city’s edge and the supply lines radiating from this carry at the most only three or four thousand volts. There are, however, certain plants in various sections that employ processes of electrical smelting, and in nearly every case a high tension line carrying twenty thousand or fortyfour thousand volts comes directly into the plant itself to supply banks of enormous transformers that change the high voltage energy to currents of comparatively low voltage and high amperage.
Whenever this occurs, and whenever there are buildings of non-fire resisting construction situated in the immediate vicinity of these high voltage conductors the question immediately shapes itself in a fire officer’s mind: “How close to one of these can I safely operate a fire stream?” The writer, with the unhesitancy that marks the deportment of beings that rush in where angels fear to tread, once asked this question at an open round table session of a fire chiefs’ association, but this question, because of the proximity of more weighty affairs, did not receive an answer.
Information That Does Not Inform
There is available, in regard to this subject, quite an amount of information in printed form, tabulating in technical terms the results of scientific experi ments made along these lines and from consulting them we learn that a stream of water projected from a nozzle tip will carry a certain number of amperes of electrical current, when played upon a conductor, dependent upon such factors as the voltage, distance, water pressure and size of nozzle tip.
This is indeed valuable information, and does extreme credit to the investigating engineers, but is not exactly all that a fire officer would like to know when confronted with a few precious seconds in which to make up his mind to what extent he will gamble the lives of his men against losing a fire.
It is unfortunately the case in a number of high tension supply installations that there is no local cutoff or disconnecting switch, and in case of emergency the feeding sub-station must be called by phone and the operator asked to open his oil switches.
Some Personal Experience in High Voltage Wires
The writer has long sought for any possible information about the actual experiences of men who have been called upon to fight fire in the near vicinity of high tension transmission lines, but the data obtainable has not been very extensive. The following occurrences, however, are taken front our own personal experience, and are given for whatever they are worth.
Number One—City department was called to an industrial plant that had no private department, finding a roof fire on a wooden building, a few feet from the wires of a twenty-two thousand volt transmission line.
First company arriving laid line from hydrant inside plant, but a plant official attempted to restrain plugman from starting water, protesting that there was danger from the high tension wires.
Department officer in charge emphatically ordered water started, was instantly obeyed, and fire was quickly extinguished without shock or injure to pipemen. It is doubtful whether solid stream touched wires, although they were splashed by spray
Number Two—City department was called to a fire in an industrial plant, finding a fire in a lightning arrestor apparatus. This apparatus consisted of several electrolyte and oil tanks on an elevated platform in the midst of a network of steel towers and wires carrying twenty-two thousand volts. A grass fire had ignited board fence enclosure and this and platform were completely involved. One of the arrestor cylinders exploded, scattering burning oil, the flame momentarily going up as high as the steel towers, with a terrific detonation of arcing through the heated air.
“Finally, in the event that it becomes unavoidable that hose lines must be operated in the presence of severe electrical hazard there are two factors that may increase the safety of the men handling them: First, a high nozzle pressure to give the greatest working range possible, and second, the use of small nozzle tips to partially “fan” or break the streams and thus decrease their conductivity.”
The department chief, arriving first, took the two 2 1/2-gallon foam extinguishers that were carried on his car and emptied them on the burning platform, blanketing the surface around the unexploded arrestor cylinders and knocking down the fire considerably.
First company arriving laid line from a plant hydrant, but were delayed by having to force hose house door. Meanwhile second company arriving pulled off chemical line and operated it. This truck carried an old Kanawha chemical tank, from which the solution was expelled by compressed air. As this tank was filled with ordinary fresh water the use of the stream it supplied was much safer than that of a straight chemical line would have been, and by the time the 2 1/2-inch line was laid the fire was under control.
“It is unfortunately the case in a number of high tension supply installations that there is no local cut-off or disconnecting switch, and in case of emergency the feeding sub-station must be called by phone and the operator asked to open his oil switches.”
No Danger to Pipemen Through Streams
Number Three—Fire occurred in the upper portion of a frame and tar paper covered structure, two stories in height, forty by twenty-five feet, which contained a complicated electrical installation that carried a 50,000 volt current.
Roof and portion of upper story were almost instantly involved, the flames going high in the air. Plant department had two good hydrant streams operating in one minute, despite the fact that one plug, situated near the building, was inaccessible on account of heat.
During about two minutes that elapsed before high tension current was cut off a terriffic amount of arcing and short circuiting occurred in upper part of building, which was repeatedly swept by streams, with no harm to pipemen. As soon as current was off, pipes were taken up into building and fire was quickly under control, with loss of roof and part of upper story.
Heavy Shocks Through Streams on Transformers
Number Four—A one-story tar paper structure, fifteen by twenty feet, containing an experimental installation, was ignited, presumably from a short circuit, and instantly involved.
Heat from blaze broke insulators of a forty-four thousand volt transmission line overhead and these conductors fell down on the fire, making a fearful display.
Also there were situated, within ten feet of the fire, three great oil filled 3,500 kilowatt transformers, which were in extreme danger of being exploded.
Plant department quickly had two hydrant streams in operation, using nozzle tips one-inch and seveneighths of an inch in diameter, respectively, instead of the one and one-eighth inch tips ordinarily used on open Underwriters’ play pipes.
These industrial plant firemen, in the face of this combined electrical and explosion hazard, held their ground several minutes until the current was cut off, keeping one stream on the fire and the other on the transformers, at a distance of about forty feet.
During this time, the pipemen received repeated and severe shocks that nearly overthrew but did not fatally injure them.
When current went off, pipes were advanced and fire quickly finished, without damage to the big transformers other than having their porcelain bushings broken.
Stream in Vicinity of High Voltage Hazardous
From these experiences it is evident that there is a certain range from which fire streams may be operated in the vicinity of high voltage conductors without loss of human life. However, any procedure of this nature is most certainly very hazardous and in all cases, when possible, the high tension current should be cut-off before the water is started.
It is needless to say that the use of a chemical stream on a high tension wire would probably mean instant death to the operator.
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Danger of High Voltage Wires
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The writer has heard men say that they were shocked by a 220 volt current coining through a lire stream, and that a 500-volt direct current will go through a tire stream. These occurrences, if true, were probably due to the composition of the water.
Personally, the writer has held a brass Callahan nozzle that projected a tire stream on a line of 2.300 volt conductors about 15 feet from the ground and felt no shock.
Finally, in the event that it becomes unavoidable that hose lines must be operated in the presence of severe electrical hazard there are two factors that may increase the safety of the men handling them: First, a high nozzle pressure to give the greatest working range possible, and second, the use of small nozzle tips to partially “fan” or break the streams thus decreasing their conductivity.