Chapter 11: Fire-Alarms and Automatic Fire Extinguishers

Assuming that a town has a well-appointed fire brigade, equipped with the most up-to-date engines, it still cannot be considered efficiently protected against the ravages of the fire-fiend unless the outbreak of a fire can be notified immediately to the stations, and local mechanical means of suppression come into action almost simultaneously with the commencement of the conflagration. “What you do, do quickly” is the keynote of successful fire-suppression; and its importance has been practically recognised in the invention of hundreds of devices, some of which we will glance at in the following pages.

The electric circuit is the most valuable servant that we have to warn us of danger. Dotted about the streets are posts carrying at the top a circular box, which contains a knob. As soon as a fire is observed, anyone may run to such a post, smash the glass screening the knob, and pull out the latter. This action flashes the alarm to the nearest fire-station, and a few minutes later an engine is dashing to the rescue. Help may also be summoned by means of the ordinary telephone exchanges or from police-stations in direct telephonic communication with the brigade depôts.

All devices depending for their ultimate value on human initiative leave a good deal to be desired. They presuppose conditions which may be absent. For instance, an electric wire in a large factory ignites some combustible material during the night. A passer-by may happen to see flames while the fire is in an early stage. On the other hand, it is equally probable that the conflagration may be well established before the alarm is given, with the result that the fire brigade arrives too late to do much good.

What we need, therefore, is a mechanical means of calling attention to the danger automatically, with a quickness which will give the brigade or people close at hand a chance of strangling the monster almost as soon as it is born, and with a precision as to locality that will save the precious time wasted in hunting for the exact point to be attacked.

Mr. G. H. Oatway, M.I.E.E., in a valuable paper read before the International Congress of Fire Brigades in London in 1903, says that the difference between the damage resulting from a fire signalled 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 “burn out.” The reformer, he continues, who aims at reducing fire waste must turn his attention primarily to hastening the alarm. The true cure 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 occur, and to check them before they have grown beyond control. He cites the fire record of Glasgow of 1902, from which it appears that three fires alone accounted for 40 per cent. of the year’s total loss, ten fires for 73 per cent., and the other 706 for only 27 per cent., or an average of £72 per fire. Had the first three fires only been notified at an earlier stage, nearly £72,000 would have been saved. Captain Sir E. M. Shaw, late Chief of the London Fire Brigade, has put the following on record: “Having devoted a very large portion of the active period of my working life in bringing into general use mechanical and hydraulic appliances for dealing with fires after they have been discovered, I nevertheless give and have always given the highest place to the early discovery and indication of fire, and not by any means to the steam, the hydraulic, or the numerous other mechanical appliances on which the principal labours of my life have been bestowed.”

A fire given fifteen minutes’ start is often hard to overtake. Imagine a warehouse alight on three floors before the alarm is raised! Engines may come one after another and pour deluges of water on the flames, yet as likely as not we read next morning of “total destruction.” No stitch in time has saved nine!

The sad part about fires is that they represent so much absolute waste. In commercial transactions, if one party loses the other gains; wealth is merely transferred, and still remains in the community. But in the matter of fire this is not the case. Supposing that a huge cotton mill is burnt down. The re-erection will, it is true, cause a lot of money to change hands; but what has resulted from the money that has already been put into the mill? Nothing. So many hundred thousands of pounds have been dematerialised and left nothing behind to represent them. The great Ottawa fire of a few years ago may be remembered as a terrible example of such total loss of human effort.

THE HISTORY OF FIRE-ALARMS

The first recorded specification for an automatic detecting device bears the date 1763. In that year a Mr. John Greene patented an arrangement of cords, weights, and pulleys, which, when the cord burnt through, caused the movement of an indicating semaphore arm. As this action appealed only to the eye, it might easily pass unnoticed, and we can imagine that Mr. Greene did not find a gold mine in his invention.

Twenty-four years later an advance was made when William Stedman introduced a “philosophical fire alarum.” “His apparatus consisted of a pivoted bulb having an open neck, and containing mercury, spirit or other liquid. 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, whilst an advance upon the first referred to, is quite impracticable. Evaporation of fluid, expansion of mercury, a stiff crank, or other causes which will readily occur to you, and the thing is useless.”[14]

In 1806 an automatic method for sprinkling water over a fire appeared. The idea was simplicity itself: a network of water mains, with taps controlled by cords, which burnt through and turned on the water. William Congreve patented, three years later, a sprinkler which was an improvement, in that it indicated the position of the fire in a building by dropping one of a number of weights. But string is not to be relied upon. It may “perish” and break when no fire is about, and any system of extinction depending on it might prove a double-edged weapon.

The nineteenth century produced hundreds of devices for alarming and extinguishing automatically. All depended upon the principle of the expansion or melting of metal in the increased temperature arising from a fire. At one time the circuit-closing thermometer was popular on account of its simplicity. “Its drawback,” says Mr. Oatway, “is the smallness of its heat-collecting surface, its isolation, and, last and worst of all, its fixity of operation. In thermometer or fuse-alarm practice it is usual to place the detectors at intervals of about ten feet or so, so that a room of any size will contain a number. If a fire breaks out, 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 composition of the solder or shifting the wire, an actuating point must be selected which is high enough to give a good working margin over the maximum industrial or seasonal heat 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° Fahrenheit, it will be clear to every one 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 degrees of a rise to wait for; whilst if it happens to be a winter’s night, the alarm is held back for a rise of perhaps 120°. What chance is there in this case for a good stop?”

Mr. Oatway has examined the fuses under different conditions, and his conclusions are drawn from practical tests. Great intelligence will not be required to appreciate the force of his arguments. Inasmuch as the rise of temperature caused by a fire is relative, during the early stages at least, to the general heat of the atmosphere, it becomes obvious that an automatic fire-alarm should be one which will keep parallel, as it were, with fluctuations of natural heat. Thus, if the “danger rise” be fixed at 100°, the alarm should be given on a cold night as certainly as at midday in summer. It was the failure of early patterns in this respect that led to their being discredited by the fire-brigade authorities.

The writer already quoted has laid down the functions of a perfect alarm:--

(a) To detect the fire at a uniformly early period, under all atmospheric and industrial conditions.

(b) To give the alarm upon the premises, and simultaneously to the brigade, by a definite and unmistakable message.

© To facilitate the work of extinction by indicating the position of the outbreak in the building attacked.

The “May Oatway” alarm has got round the first difficulty in a most ingenious manner by adapting the principle of the compensation methods already described in connection with watches.

The alarm consists of a steel rod of a section found to be most suitable for the purpose. To the side is attached by screws entering the rod near the ends a copper wire, which is long enough to sag slightly at its centre, from which depends a silver chain carrying a carbon contact-piece. A short distance below the carbon are the two terminals of the electric circuit which, when completed by the lowering of the carbon, gives the alarm. Now if there be a very gradual change of temperature the steel rod lengthens slowly, and so does the copper wire, so that the amount of sag remains practically what it was before. But in event of a fire the copper expands much more quickly than the steel, and sags until the carbon completes the circuit. The whole thing is beautifully simple, very durable, quite consistent, and reliable. As soon as the temperature diminishes, on the extinction of the fire, the alarm automatically returns to its normal position, ready for further work.