AUTOMATIC FIRE ALARMS.
Their Evolution, Necessity and Advantages.
In a paper read at the International Fire Prevention congress recently held in London, England, G. H. Oatway, of Glasgow, Scotland, insisted upon the necessity for automatic fire alarms, with direct communication to the headquarters of fire departments. Taking for his theme the $65,000,000 annual fire-waste in the United Kingdom, he argued for the general installation of such automatic systems, and assumed as an axiom, that, “other things being equal, the measure of loss will invariably depend upon the hold the fire has obtained before its existence is discovered, and that anything which expedites the alarm is a direct advantage.” Hence, “the difference between the damage resulting from a fire signaled in its early stage and the same fire reported when it has spread to two or three floors is often the difference between a nominal loss and a burnout.” For which reason, “the reformer who aims at reducing fire-waste must turn his attention, primarily, to hastening the alarm. The true crux of the matter is, not what quantity of gear it takes to deal with huge conflagrations, but how to concentrate at the earliest stage upon the outbreaks as they oc^ur, and to check them before they have grown beyond control.” The figures of fire-waste everywhere show that, if immediate notice is given of a fire, and it is attacked in its earliest stage, the loss both by fire and water is very considerably less than it will be at any subsequent period, even if only a few minutes later. Looking at this very obvious feature it was a matter of astonishment to the writer, who is a “colonial,” on coming to the British Isles three years ago, to find, not only that there were no automatic alarms installed as a defence against fires not detected in their incipiency— consequently against fire-waste—and, therefore, not signaled to the fire departments, but actually no street alarms in operations. Mr. Oatway then spoke of the evolution of the fire alarm system in England from the year 1763, when John Greene patented the first automatic detecting device—an arrangement of cords, weights, and pulleys, and their aim— namely, the operation of an indicating arm when the cord burned and allowed a balance weight to fall. No provision was made for any audible alarm, and it remained for someone to notice the altered position of the semaphore before any advantage could be taken of it. In 1787 followed an audible alarm, the “philosophical fire alarm” of William Stedman, whose apparatus consisted of a pivoted bulb having an open neck, and containing mercury, spirit, or other aquiform fluid. As the heat of the room increased, the expansion of the fluid caused it to spill over, release a trigger, and allow a mechanical gong to run down. This arrangement was right in theory, but impractical in management, owing to the possibilities of the fluid evaporating, the mercury oxidising, or the crank being too stiff to work. The year 1866 saw the birth of the sprinkler system—a reticulation of mains controled by a lever kept in a closed position by suitable cords, which, when burned through, or severed, or sufficiently weakened in any way, caused a deluge of water. In 1809 William Congreve patented a combination string (still the same old string) and solder alarm to act in conjunction with a sprinkler or water main system. The water lever fell when the cord in any room let go from whatever cause; the water flowed; and the weight down showed where the fire was. Of course today such a contrivance would be laughed at, as neither string nor soft solder under tension are reliable for any length of time, and, with a fixed call or actuating point of no degrees, the result was bound to be disastrous. Many more such devices were patented; most were possessed of some merit; few, however ingenious in their details, had any promise of permanency. The majority of them aimed at local alarm only—that is to say. they rang a bell, lowered a semaphore, or did something at a given temperature. All the devices could be broadly classed under two heads—automatic alarms and automatic sprinklers. The latter, however good their record after 100 years of evolution, “have serious limitations,” and, however, helpful, cannot supersede the automatic alarm, whose actuating principle is the increase of temperature due to the fire—a “certain quantity”— and one which, “if properly applied, can be absolutely relied upon.” By not being properly applied they are mischievous, and in Mr. Oatway’s eyes the most mischievous is the “circuit-closing thermometer.” whose drawback is the “smallness of its heat-collecting surface, its isolation, and, last and worst of all. its fixity of operating point.” This objection applies to all non-compensated automatic detecting appliances. “In thermometers, or fuse-alarm practice, it is usual to place the detectors at intervals of about ten feet, so that a room of any size will contain a number. If a fire breaks out, the room rapidly warms up. The ceiling is blanketed with heat, and every detector feels its influence. Each is affected, but none can give the alarm until some one of the number absolutely reaches the set point or melts out. Having no means of varying the fusing point of the solder, or of shifting the wire in the thermometer tube, an actuating point must be selected, which is high enough to give a good working margin over the maximum industrial or seasonal temperature of the year, and thus it comes about that, if the fire breaks out in winter or when the room is at its lowest temperature, the amount of loss is considerably and quite unnecessarily increased. In a device set to fuse at 150° Fahr., it will be clear to everyone that the measure of the damage will depend upon the normal temperature of the room at the time of the outbreak. If the mercury is in the nineties, there is only some sixty-degree of a rise to wait for; whilst, if it happens to be a winter night, the alarm is held back for a rise of perhaps 120 degrees; what chance is there of a good stop? * * * In a climate which does not maintain a uniform temperature a dead level alarm is unfair to one period of the year or the other. It is too high for some months or too low for others, and I think it is beyond question that the false alarms or unsignaled fires which have earned for the earlier automatic detectors their unenviable reputation and led to their exclusion or removal from brigade stations is due to this cause.” A perfect automatic fire alarm system should perform the following functions: (a) Detect the fire at a uniformly early period under all atmospheric or industrial conditions; (b) give the alarm upon the premises, and simultaneously to the brigade by a definite and unmistakable message; and (c) facilitate the work of extinction by indicating the exact position of the outbreak in the building attacked. For the first of these functions Mr. Oatway employed a detector, which by its own expansion or contraction automatically maintains the uniformity of the rise necessary to produce the alarm under any and every working condition. The detector consists of a steel rod of rather unusual form and cross-section, to which a copper wire seven feet in length is attached: and at the centre of the combination a contact tube holding the carbon bridging piece is placed. The latter is suspended by a silver chain to the detecting wire, and is held at a distance above two platinum terminals attached to the steel rod. The distance between the two is determined by the margin of rise for the alarm. This in practice is usually twenty-five degrees Fahr. The detecting wire is yoked to the compensator, in order that the expansion of the one may equal the expansion of the other, so long as the heat rise is the comparatively gradual one due to gas light, the radiators, or other normal causes. The degree of elongation differs slightly in extent, it is not a mathematical fixture, but the approximation is so close that the pair works well, and affords an “absolute immunity from false alarm and ability to respond to a satisfactory heal test at any time.” The expansion and contraction of the two are equal in the matter of lengthening or shortening. but the difference is in speed. If a fire breaks out, the copper wire is off long before the compensator can overtake it, and the work is done. If the rise is simply gradual and “due to natural causes, the ends of the pair will poke out a little, just as they will crawl back again when the temperature diminishes, but in the centre, where the contact is made, is equilibrium, and the twenty-five-degree expansion necessary to insure contact is automatically maintained and never interfered with. It is only when the one moves before the other can be actuated that the gap between the contacts is closed and the signal dispached.” This signal is by bells or gongs and rightly performs the second function of an automatic fire alarm system, thereby reducing the chances of disaster from loss of life in large or small establishments. Mr. Oatway quoted the instance of one large warehouse where 600 of these “nerve centres” are “all yoked up to four positionindicators, three of which repeat upon the master indicator; and this, in turn, controls and actuates the local alarms and telegraphs the central fire station.” The method of calling them is simple. There is an automatic transmitter, and the code cipher it is intended to send is cut upon the periphery of a disk So long as the unindented edge of the disk is between the printing key and the printing point, there is no message; but, so soon as this armature is pulled down by the current switched on by the automatic detector described, then away goes the disk; a legibly engraved shutter is dropped in the central fire station, and the code cipher is repeated four times, instantly calling out the brigade. The shutter and Morse code were used in combination at the request of the Professional Fire Brigades association, so as to avoid the possibility of any misreading of the telegraphic signal. The shutter by itself is less dependable, because “an outside contact upon the line would bring it down, but no other cause than a consistently closed circuit in the building can give the four times repeated telegraphic signal of fire.” This device also performs the third function of an automatic fire alarm—namely, by indicating the exact seat of the fire and thereby facilitating its extinction by concentration of the firemen’s efforts on the actual danger spot, while at the same time the amount of damage by fire and water is limited. The details employed are simple. There are as many rows of shutters as there are floors in the building, and as many shutters as there are rooms. As each room is affected, its indicator is actuated, and thus the whole area of the fire, with the direction it is taking, if spreading, can be seen at a glance. By means of such automatic fire alarms, therefore, “shortness of gear and shortness of water can best be counterbalanced by hastening the period of attack, and this necessitates the hastening of the alarm.” They also counterbalance that too great tendency on the part of untrained employes to trifle with fires, since many buildings are lost every year through the misplaced confidence of inmates in their ability to deal with the outbreak. At the same time “there is nothing in any automatic system to discourage individual effort; inmates can put the fire out, if they can, but, in any case, the fire department gets timely and definite notice,” and if on arrival it finds the fire extinguished, so much the better. This is the common sense view of it. Helpers work none the less intelligently because they know the brigade is coming; and it is necessary to provide some automatic method of calling them, because no one can ever rely upon any body who is unfamiliar with fire doing the right thing at the time.