The Fire Hazards of Popular Radio
How Best to Avoid Them—Various Dangers Described and Methods of Rendering Installations Safe Pointed Out—Advances Predicted
THE modern and progressive fire chief must reckon with the wireless both as a hazard and as an assistance to his fire department work. The following paper treats of the radio from the standpoint of its fire hazards:
Widespread application of radio in the entertainment, educational and publicity fields, with its general establishment throughout the country of radiophone broadcasting stations, furnishing daily popular programs, and coupled therewith, a renewed and increasing interest in amateur radio, has multiplied materially the mere number of potential fire hazards in our residential districts.
It is not the present purpose to proclaim that thus a very serious and material hazard has been added to our already sufficiently numerous evils; but rather to attempt to set forth wherein the hazard lies, and to show that with reasonable vigilance, it need not be great. This latter statement is indeed substantiated by the small number of electric fires ascribed to radio in the past year, in spite of the amazing increase in the number of radio stations installed.
Inasmuch as by far the greater number of such stations are receiving stations in residences for the reception of popular broadcasting, the essentials of such stations, the general classification of apparatus affording such essentials and the hazards thereof will first be taken up.
Essentials of Radio Receiving Stations
The essentials of a radio receiving station are: First, something to extract from the electric field surrounding the earth a portion of the energy thereof; second, something to pick out from such extracted energy a particular portion, the variations in which constitute the signals it is desired to receive; third, something to convert this energy to audible sound and so detect it.
The first essential may be called in a most general way the “antenna.” An antenna may consist of a wire or group of wires or a plate of metal, suspended in the air out of doors, with a lead-in running to the radio set inside the house; or it may consist of a similar wire or wires entirely within the house, which may be stretched in the attic or around the room, or may be wound on a pair of crossed sticks, or similar supporting device (the so-called loop antenna), or again, existing wiring in the house, such as the electric light, bell or telephone circuits may be utilized. Again, the antenna may be a piece of insulated wire buried in the ground or merely a wire leading from the receiving set to the water pipe or other grounded metal. The ground itself has not been mentioned as an essential, for the reason that direct connection to it is not necessary for good reception of radio signals, nevertheless, even when not connected, it is effective to a greater or less extent by inductive actions, through the air.
Hazard of Outside Antennas
The principal hazards of outdoor antennas may be enumerated as follows:
Installation in proximity to other wires which are charged or may become charged by contact with charged wires elsewhere, so that breakage of the antenna, due to its own weakness, or due to falling limbs or structures may cause it to cross such charged wires and so bring dangerous electrical conditions into the house.
Inadequate insulation which may invite trouble during thunder storms.
The lightning hazard, the elevated conductor is itself a species of lightning rod, and with proper insulation and adequate, well maintained lightning arrester or ground switch and ground connection is a protective device rather than a hazard; but with poor insulation or none, or an inoperative arrester or ground-switch or with too small a ground-wire or with an inefficient ground, it is quite possible that lightning could cause considerable trouble. However, let it be said that there are in long common use metal clothes lines, installed on flat roofs and run between buildings, with no pretense of grounding, which afford an equal lightning hazard.
“It is not the present purpose to proclaim that a very serious and material hazard has been added to our already sufficiently numerous evils; but rather to attempt to set forth wherein the hazard lies, and to show that with reasonable vigilance, it need not be great.”
Hazards of Inside Wire Antennas
The hazard of the inside wire antenna is very slight, residing chiefly in careless installation, so that it may come in contact with lightning or power wires in the building.
The use of existing service wires inside the house for antennas, particularly the electric light or power wires carries the hazard of accidental leading of the service current into the radio circuit, either by inadvertent wrong connection or by the breakdown of the insulation of the condenser device used for purposes of connection. Practically no hazard resides in the use of either the loop, the buried wire or the ground lead antenna.
It will be-at once seen that the remedy for antenna hazards is anti-carelessness. A secure, well insulated antenna in a safe location, with proper arrester and ground connection, need cause no worry.
Second Essential Is Tuner
The second essential is the energy selecting apparatus or tuner. This is practically a small coil of wire, with a variable number of turns, with or without an electrical condenser, which latter is usually a bunch of metal plates in close proximity but insulated from each other in two groups, the insulator is either air, oil or some solid material. There is no direct fire hazard in this apparatus by itself.
The third essential is the device for converting the received electrical signal into sound. The simplest type is a crystal, held lightly in contact with a piece of metal and the whole connected in series with a telephone. There is no fire hazard in this type of detector.
Hazard of the Detector
The other, and most desirable type of detector, is the thermionic tube, which is a species of electric light bulb containing one or two internal electrodes insulated from each other and from the filament. These usually require two separate batteries for their operation, and either storage or primary cells may be used. Storage batteries of from two to six volts are perhaps most commonly used for lighting the filaments, while dry batteries of from twenty to one hundred volts are used for operating the telephone circuit. The telephone is used just as with the crystal detector, or more than one tube may be used and a loud-speaker or giant telephone used in place of the small head set. Each tube used usually has an adjustable rheostat to regulate the filament current, and often a similar higher resistance device is used to regulate the telephone battery potential.
The hazards of these devices are the usual hazards of low potential electric circuits. With dry batteries, there is little or no hazard; but a fresh, small, one hundred volt, telephone battery can draw an arc that will set fire to various insulating compounds. Storage batteries of the sixty to one hundred ampere hour size can deliver a very husky current on short circuit and careless or accidental wrong connections have been known to burn out rheostats and coils and even to start a blaze on the insulation of No. 14 rubber-covered wire when the wire fused off on short circuit. Care in installation, and the use of fuses at the battery terminals, will reduce these hazards to a minimum.
Storage batteries usually contain sulphuric acid; this is not strong enough to have any elements of fire hazard; but it will destroy clothing and wood work, and is unpleasant at least in contact with the skin.
Sometimes Hazard in Ground Wire
The hazard of the ground wire is ordinarily slight, but such wire should be large enough to carry any accidental current it might receive, and to resist being broken or detached easily. It should be securely attached to the ground (preferably the water service) by a proper clamp. The gas service should not be used for a ground. Any made ground should be the same as would be installed for an effective lightning rod.
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All of the above hazards, and possibly others, have been taken into account by the underwriters in the rules they published last year for the provisional regulation of radio receiving installations. Inspectors, whether from underwriters or from fire departments, should insist on a full compliance with those rules, which, if effected, will make the radio receiving station fire hazard a trivial one.
The Amateur Sending Station
It is now in order to say a little about amateur sending stations, such as may be found in private houses or outbuildings mostly operated by an enthusiastic junior contingent of high school or college age. Right here the writer wishes to pay a compliment to the young people engaged in amateur radio during the past fifteen years; the advances made in the art, and the achievements in extending world communication, can be largely traced back to radio amateurs who began their research as boys. The average high school boy of today knows more and better about the theory and practice of electrokinetics than did the graduate electrical engineer of thirty years ago, and this largely by reason of his work with radio.
Without going into details of various radio sending apparatus, let us consider that a radio sending station must have an antenna, a source of power, a device for generating and regulating electromagnetic waves and a means of impressing voluntary signals thereon.
Many of the hazards of such a station are exactly like those of the receiving station, and will not be re-enumerated; suffice to say that for sending, materially higher voltages are used, and greater precautions regarding insulation must be observed. The smaller stations frequently use batteries for the source of power, which again puts them within the general hazard class with the receiving station.
High Voltage in Sending Station
Probably the great majority of such stations, however, use the public electric service as a source of power, so that with certain exceptions, the hazards are no different than with any household electrical installation; the underwriters’ rules which make for safety in the latter case are equally effective in the former. It is, therefore, for us to consider only the exceptions as peculiar to radio. The house current which the amateur uses for his energy supply usually comes to him as sixty cycle alternating current at either 110 or 220 volts potential. Now, in order to send out radio signals on 200 meters wave length, which is the maximum allowed the junior amateur by Uncle Sam, he must have 1,500,000 cycle alternating current, and if he wants to cover any considerable distance, he must have more than 220 volts. There are various ways of stepping up the frequency and voltage, utilizing transformers, induction coils, spark gaps, motor generators, thermionic tubes, electrolytic rectifiers, batteries, condensers and various combinations of them; but all of them are in effect some sort of a step-up transformer, coupled with a condenser to form an oscillating circuit, with some sort of an automatic controllable power impulse device which will feed the energy into the oscillatory circuit, in exact rhythm for the wave length wanted. Here again, except for somewhat unusually high voltages to be found in a dwelling house, there is nothing materially different about the hazards of the apparatus itself, from those of similar electrical devices found in garages, battery stations, hospitals and doctors’ offices.
Principle Hazard Is Home-Made Work
The principal hazard is, perhaps, that much of this apparatus is home-made, and the best of materials and best of skill have not been used. Let me say, though, that I have seen apparatus constructed by young amateurs that could not have been bettered either in material or workmanship by the most skilled electrical artisan; even the design would have been creditable to an electrical professor.
The really exceptional hazard is a function of the remarkably high frequency used. If the antenna runs near and parallel to lighting or telephone circuits, the induction is liable to build up a voltage in such utility circuits as to break down insulation and
possibly cause a fire. Sometimes, the high frequency current works back through the transformer, in such a way as to induce high voltage and surges on the house circuit, which may cause a breakdown in insulation, at a point relatively remote from the radio set.
The danger can all be avoided by keeping the high frequency circuits remote from or at right angles to all other house circuits, and by a proper use of condensers, choke coils and leaks or vacuum gaps, to prevent the high frequency from getting back into the electric service supply.
Another exception is more a matter of personal safety than fire hazard. The high voltage, high frequency current is not particularly dangerous to life but it is painful and can burn. However, there is often around such stations, wires carrying 1,000 volts or more of sixty cycle alternating or even of direct current, the touching of which might mean death. In case of a fire in a radio sending station, the power supply should be promptly cut off, to insure that no fireman comes in contact with any very innocent looking but really very deadly little wire festooned over a radio sending set.
Future Advances in Radio Broadcasting
The advances in radio broadcasting in the last year have been wonderful, but hardly a patch on its possibilities as a means of entertainment, publicity, and education has been touched. We may look for accelerative advances from now on, with corresponding increase in its popular use. Its growing use in fire stations, as a means of recreation, should be pleasing to all humanitarian instincts and duly encouraged. Its possibilities in these same fire stations, as an educational measure, cannot be estimated. I do not refer to education along fire lines alone; but to that broad education in citizenship and manhood which it is perfectly possible to have broadcasted in person, to all who care to listen, by the world’s foremost men.
Radio Communication By Fire Department
My good and progressive friend. Chief Taber, tells me that already the Boston fire department has a radio course in their school, and that very shortly the fireboats will be in constant communication with headquarters by radio. It is but a short step to where every fire station in the city has a receiving set with a loud speaker, which, with a radiophone on the transmitter at headquarters, puts every man on duty in hearing of his chief’s voice at short notice. Under such circumstances, I will add one other radio hazard from the firemen’s standpoint, namely, the hazard of failing to do something he heard the boss personally tell him to do, in the hearing of the whole department.
(Paper read before annual convention of the New England Association of Fire Chiefs.)
Leominster’s New Water Main Will Remove Fire Hazard —The fire hazard in North Main Street, Leominster, Mass., caused by the lack of water pressure, will soon be removed, for the pipe for the new 12-inch water main to be laid in that street, is arriving on the job and the water department will soon be ready to start the work of laying the new main.