Prof. Silvanus P. Thompson, in a recent lecture, says that nothing but a self-acting or automatic system, which will operate at the right moment and at the very spot, without the intervention of any human hand, will meet the case.
Modern automatic appliances for the prevention and extinction of fire may be grouped under the following heads: - (a) automatic sprinklers; (o) automatic fire-doors; (c) automatic alarms; (d) miscellaneous appliances.
(a) Automatic Sprinklers: - Foremost and most important of modern appliances stands the automatic sprinkler. Briefly, it is a species of self-acting valve connected with a system of water pipes placed in the ceiling of a room, which, on the outbreak of a fire, open and distribute water in a shower of spray exactly at the place where the fire breaks out. It is also usually arranged so that, whenever it is called into operation by the heat, it sounds an alarm bell, and summons aid to the spot. It is both fire extinguisher and fire alarm in one. Concerning it, Edward Atkinson, president of the Boston Manufacturers' Mutual Fire Insurance Company, says, " we consider the automatic sprinkler the most valuable auxiliary appliance, the best fire detector, the watchman who never sleeps, and the device which is least likely to be out of order when needed."The saving effected in New England alone during 8 years by the introduction of sprinklers is calculated to amount to 300,000/., and their use is extending every day.
The introduction of sprinklers reduces the risk of conflagration by fire to less than a twentieth part.
The earliest suggestion for the automatic distribution of water in a building appears to have been made in 1806 by John Carey, of London, who took out a patent for " tfee extinguishment of fires in gentlemen's apartments and warehouses " by means of rose sprinklers connected by pipes with a rain-water tank. Valves weighted to open, but held back by a combustible cord, were placed near the ceiling, so as to burn and turn on the water. A few years later, Sir Wm. Congreve took out patents for a system of distribution of water by bulbs, roses, or perforated pipes, supplied by water-mains through valves operated from outside. He also proposed to work valves automatically by cords, which were secured with "a cement fusible at 110° F. or less."
In 1852, William Maccaboy proposed a kind of sprinkler, in which the water was distributed by a rotating "mill" like a Hero's engine, covered with a cap of lead, guttapercha, or fusible alloy. Rotating sprinklers have been subsequently patented by Granger, Parmelee, and others.
In 1861, Louis Rough ton patented a sprinkler having a rose-head with a neck plugged with a fusible substance, such as fusible alloy, or a mixture of wax, resin, and stearine.
In 1864, Captain A. Stewart Harrison, of the 1st London Engineers, produced an excellent form of automatic sprinkler, which embodied a good many of the principles in the more recent forms. Harrison's sprinkler consisted of a rose, through the perforations of which the water would be forced; but an internal valve held back the water, the valve itself being secured by solder. But it should be noted as an important point that Harrison secured the valve at the lowest point of the sprinkler, outside the rose, by a stem, which passed downwards through the sprinkler.
Another form of sprinkler, introduced by F. W. Whiting, has a conical or hemispherical rosette, covered by a thin metal cap, soldered all round the edge. The water pressure tends to tear the soldered flanges apart.
It may be here remarked that 100 sq. ft., i. e. an area 10 ft. square, forms a convenient unit of reference in connection with the distribution of water by sprinklers.
There Were several powerful objections to the methods adopted up till that time. With impure water the perforations of roses or pipes were liable to choke; and in the case of iron pipes, rust produced the same effect. The ingenuity of inventors was called out to meet these difficulties. Harrison countersunk the orifices in his rose; Whiting patented a plan of letting eyelets of brass into the orifices; Burritt devised a method of dislodging sediment or dust, by means of a thimble with a rounded end, which when detached by the melting of the solder, is churned round inside a perforated rose by the action of the water.
A more serious defect was that the water in the sprinkler or pipe, by its near presence to the solder, abstracted the heat and delayed the opening of the valve. This had indeed been positively obviated in the forgotten sprinkler of Harrison, by the interposition of a block of wood between the water-valve and the soldered joint on the stem.
Another defect arose in some cases, where rubber was used as the material of the valve, from the clogging of the valve on its seat. Woodbury, who made a most exhaustive series of tests for the Boston Manufacturers' Mutual Insurance Company, on sprinklers of all kinds, states that it required a pressure of 65 lb. per sq. in. to make some of these valves open.
In 1875, the Boston Manufacturers' Mutual Company issued a pamphlet recommending sprinklers to their clients, although the chief forms to that time were comparatively imperfect. But their use spread rapidly from that date.
In 1874, H. Parmelee introduced a sprinkler which, though now superseded by more sensitive arrangements, did good service, and is still in considerable use It consisted of a metal cap sealed down with fusible solder over an upright revolving turbine-jet. At a pressure of 10 lb. per sq. in. this sprinkler discharges 1 1/2 cub. ft. of water per minute.
The obvious requisites of a good sprinkler are that the solder should fuse at a low and well-defined tempera-, ture, without any appreciable prior softening; that the mechanism should not be liable to get out of order or stick; that the parts opened by heat should be capable of ready replacement without skilled labour; that there should be no leakage at the valve; and, last])-, that the quantity of solder to be melted should be small, and so placed that it is not cooled by contact with too great a mass of metal, or exposed to the drip of the opening valve.