What is an automatic fire sprinkler system, it is a fire-fighting system designed to be operated by the fire itself so a as to dispense water in the areas where it is needed to ensue rapid suppression of the fire with the minimum of damage to property. The salient feature of the system is an adequate water supply which may be pumped through a range of supply pipes, usually at ceiling level, to a series of heat sensitive 'sprinklers' which are designed to respond to the thermal conditions created by the fire.
Therefore, only the fire sprinklers which have been affected by the fire will be operated and will allow water to flow from them and distributed in the form of a water spay onto the fire below. Each sprinkler is intended to cover up to about 12m2 for normal risks commercial risks such as Schools or Shopping Centres. Fire sprinkler system, while simple in principle have been developed using a vast amount of ingenuity and experience over a period of more than 100 years in order that it may respond rapidly and reliably to fire conditions while being relatively free from faulty operation.
History of the Sprinkler
In the late 18th centuries the need was felt for a system of fire protection in buildings which was always 'on guard', so that the shortcomings of the haphazard system of Fire Watchmen and manually operated fire appliances with ineffective and unreliable equipment could be mitigated. One of the earliest systems is described by Benjamin Wyatt, FSA, Architect, and was installed in the Theatre Royal, Drury Lane, in 1812. At this time, when it took ships of the line in the Royal Navy some three hours of manual labour to weight anchor as they contained no mechanism other than a hand-operated bilge pump, the system must have been a considerable achievement. It consisted of a
'cylindrical airtight reservoir of 400 hogshead underground at the back of the building, fed by a 10 inch main which branched to all parts of the theatre through a series of transverse pipes each pierced by a series of half inch diameter holes in three rows so as to pour down 2,000 streams of water each equal to that of a small fire engine'.
The reservoir was implemented after the first ejection of water by use of the 75 horse power steam engine of the Water works, the management of which contracted with the theatre 'to set their engine in full action into the reservoirs in less than 20min on any alarm being given.' The water was turned on by a series of valves, which could be operated manually when the fire was discovered. The theatre was divided into sections, so that water need only be discharged in the section affected by fire. They system was designed by Colonel William Congreve and is covered by Patent No. 3606 dated 1812. In subsequent years, many similar patents based on the use of gravity tanks and distributing pipework were suggested. For the protection of ships and buildings in these patents, the essential feature of the sprinkler system was added, that is, the opening of perforations in the pipe or the operation of 'valve boxes' or spray heads by the action of the fire itself. The opening of the perforations or the operation of the valve boxes was usually due to the melting of a plug made of guttapercha, fusible metal or a fusible compound such as mixture of wax, resin, stearine or like substances 'mixed in such proportions as to melt at a temperature not less than 100 degrees fahrenheit'. Thus the essential elements of the modern sprinkler system were born.
In America, the perforated pipe system was first used in 1852, the earliest systems being meant only to protect the roofs of textile-mill buildings. later they were extended to protect picker, card and spinning rooms where rapidly developing fires were common. Indeed, it was the need of the textile industry which provided the main impetus for the development of the sprinkler system. in later perforated pipes systems, holes of 1/10in were used, some 9in apart on alternate side of the pipes, which were mounted just beneath the ceiling. Thus, when the valves were operated the holes squirted water upwards onto the ceiling, from which it fell to cover the floor below. But the major disadvantages of the perforated pipe system sounded its death-knell. It was not selective enough in applying water only to the fire, so a small automatically produced heavy water damage. The holes were readily clogged with dirt or sediment, and the system could not be tested without causing water damage. Also, the task of clearing blockages was a formidable and recurring one. But occasionally the perforated pipe system was successful in controlling fire, and this ensured that protective systems were not rejected altogether.
Instead, the latent potential of the inventors was realised in the first automatic sprinkler, invented by Major A. Stewart Harrison of the First Engineer Volunteers, London, in 1864. The sprinkler was a hollow perforated brass ball or shell of 20 or 3in diameter. A plunger running through the shell from bottom to top held a soft rubber valve in place in an orifice in the supply pipe, and was itself held in place by a retaining string, as shown in the Figure. This feature made it automatic since the flames from the fire would burn through the string and allow the plunger to fall, thus opening the valve. Water was then ejected under pressure from the perforations in the wall of the ball, over the area where the fire was. The Harrison was a more sensitive sprinkler than some later types, but it did not attract attention, possible because the American States were preoccupied by the Civil War
Ten years were to pass before the first automatic sprinkler to be widely used was invented by Henry S. Parmelee of Connecticut, who objected to the rise in the cost of the insurance of his piano factory following the disastrous fires in Chicago in 1871 and in Boston in 1872. After preliminary designs, had failed, he produced in 1875 a simple model having a downward-facing perforated distribution shell on a heavy base. A brass cap normally covered the shell and was affixed to the base with a solder of melting point 160 Celsius. When the solder melted, the cap was pushed of by water pressure and the water was distributed onto the fire below. As might be expected, the sprinkler took several minutes to operate because of the mass of the base and the water contained within the shell, which conducted the heat away. An improved version of 1878 had a rotating serrated wheel to distribute the water and continued to be sold until 1882, when some 200,000 had been installed, mostly by the Providence Steam and Gas Pipe company. This Company was headed by Frederick Grinnell, who in 1882 introduced the first of a series of much improved sprinklers to his own designs. Meanwhile, the insurance aspects of sprinkler protection were being put on a sound footing. When existing insurance companies would not insure the cotton mills of New England, a number of forward thinking mill owners banded together to form their own mutual insurance companies. Each owner undertook to do everything in his power to prevent or control fire loss and the owners together provide the indemnity for the losses which did occur. The new mutual companies, now the Factory Mutual System, took a lively part in promoting the design, development and installation of sprinkler systems.
In the United Kingdom, the ‘Parmelee’ Sprinkler was installed in the Edinburgh Rubber Works in 1881, the first sprinkler to be recognised by the insurance offices. It was in the Lancashire cotton spinning mill, however, that sprinklers were mostly installed, and native designs soon replaced the ‘Parmelee’. The ‘Vulcan’ was designed by Mr. J. H. Lynde of Manchester and like the ‘Parmelee had a fusible cap which allowed a central spindle to drop, opening the valve and allowing the deflector plate to assume its correct position for spraying water, the distribution being improved by the deflector spinning on the spindle. Another sealed type sprinkler was the ‘Simplex’ invented by Messrs. Dowson and Taylor of Bolton. The central tube, with deflector attached to its lower end, acted an s valve because its closed end butted into an orifice inside the body. The outer fixed tube was soldered to the central tube and when the solder melted, the latter fell with the deflector into the extended position. John Taylor later joined the firm of Marther and Platt Ltd.
Another interesting sprinkler is shown in Figure 5. In this a fuse trailed from the sprinkler head to the floor, so that a fire would ignite the fuse and cause a small charge in the side canister to explode, thus opening the sprinkler valve. The fuses would be reeled up close to the ceiling by day, but would be allowed to trail at night to give protection. While this arrangement has obvious shortcomings, the principle is a good one and has been successfully in the zoned sprinkler system for the protection of high-racked shortages.
In the original American ‘Grinnell’ sprinkler, the combined valve and deflector plate was held in place against the orifice in the brass diaphragm by means of a compound lever, once piece of which was secured to the yoke by solder and a pin. When the solder melted the levers fell away, the flexible diaphragm exerting a pressure on them via the valve and deflector in order to ensure quick, clean, release. Other early types of sprinkler were the ‘Hudson’, the ‘Mayall’ and the ‘Walworth’ introduced in 1889, but none of these stayed the course, being unnecessarily complex, as was also the ‘Witter’. What was needed was a straightforward ‘simple’ device of high reliability, and the later Grinnell types fulfilled the essence of the requirement.
Sprinklers were first installed in Australia in 1886 by Mather and Platt using the Grinnell system and in New Zealand in 1889. From 1889 their agents in the two countries were Russell and Wormald, a partnership which in 1911 became the firm of Wormald Brothers. The Wormald of the partnership was the brother of John Wormald of Manchester, England, who wrote the first ‘rules for the installation of Sprinkler systems, as described below. The system installed by Mather and Platt in the bedding factory of Laycock, Son and Nettleton, south Melbourne, Victoria, in February 1886, controlled its first fire on 21st December 1886 (only four years after Grinnell had patented this system in the United States of America). Similarly, the first system installed in New Zealand, at the Northern Roller Milling Co. Ltd., Auckland, dealt with many fires.
All the Grinnell types introduced after the summer of 1891 were either of the ‘glass valve’ pattern or the ‘glass bulb’ pattern. In the former, the glass valve was flat on one side and rounded on the other. The round side was pressed into the half-inch orifice in a flexible diaphragm and the valve was held in place by a vertical strut and two leavers (hood and key leavers) all soldered together. When the solder melted in the convected heat from the fire, the levers and strut fell away releasing the valve and allowing a jet of water from the orifice to strike the deflector plate attached to the ends of the yoke arms, thus producing a spray of water droplets. In 1922 the Grinnell ‘glass bulb’ type sprinkler was introduced, mainly to avoid corrosion difficulties which occurred with the strut type. In this sprinkler, the valve was held closed by a glass bulb containing spirit, and the quantity of spirit in the bulb determined its bursting temperature when it was exposed to hot gases from the fire. The Grinnell arrangement did not readily permit control of the loading of the valve on its seating and it was replaced in 1925 by a modified type developed by Mather and Platt Ltd., which has become the basis for most, if not all, subsequent designs of glass-bulb type sprinklers. In this sprinkler, a barrel-shaped bulb is held between a hollow cone and the valve cap, so that the loading on the bulb, and hence on the valve, may be varied by adjusting a screw in the head of the cone. The cone is supported at the junction of the two yoke arms. It is now common practice for manufacturers to use a standard body-yoke arm assembly and to vary the type of bulb and deflector plate to suit the requirements. Thus figure 12 shows a range of three sprinklers all with the same body assembly but with ‘conventional’ ‘spray’, and ‘side-wall’ types of deflector plates. In the late 1950s, the Factory Mutual Engineers introduced the ‘spray’ type sprinkler, to give a broader distribution pattern but less wetting of the ceiling than was given by the ‘conventional’ sprinkler, and in this way they have achieved wider spacing of sprinklers and hence less pipework and cheaper installations in certain types of risk. The ‘side-wall’ sprinkler is used mainly for installation adjacent to walls where an offset water distribution pattern is required.
The development of the sprinkler has continued rapidly since the early 1960s to meet the changing needs of a variety of new types of risk. There are three main areas in which these developments have occurred. The first relates to the need for more penetrative sprinklers in high-piled storages, and this has been met by the development of the ‘large drop’ sprinkler. The second relates to the need for a more responsive sprinkler for use in specific life-safety applications, and the ‘fast response’ sprinkler has been developed to meet this need. The third relates to the need for more aesthetically acceptable sprinklers for use in shops, offices, hotels, restaurants and other similar applications, and to this end, miniature glass bulb sprinklers have been developed.