Sprinkler Head Closes Automatically After Putting Fire Under Control
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The sprinkler head has always been one of the best friends a fire fighter has. There are many men who are alive today only because of the efforts throughout the years by men in the fire service to obtain automatic sprinkler protection for hazardous occupancies.
In some cases there has been a reluctance to install automatic sprinkler protection because of a concern for water damage. Now, thanks to the Central Automatic Sprinkler Company, a head has been developed that opens when a fire occurs and closes automatically when the fire is controlled.
This simple operation has many potential benefits, the most obvious being a reduction in the water damage. Given the increased values of building contents, the effect of water damage on continually rising insurance rates and the potential for water damage on every floor below the fire in a high-rise building, we can begin to appreciate what this added feature to the conventional sprinkler system means.
Smaller water supply needed
The possibilities for this new device go even beyond limiting water damage. The fact that the heads close as the fire is controlled also means that fewer heads operate at one time. This benefit can easily be translated into a reduced water supply requirement for a sprinkler system equipped with on-and-off heads since the needed water supply is based on the number of heads that will be operating at one time. When this improvement is recognized and credit is reflected in the design of the system, the end result will be a reduction in cost.
This advantage will hopefully influence building owners to install automatically sprinklers who previously were unable to do so because their properties were not large enough to warrant the expense. We are talking about buildings of 10,000 square feet or less with contents of considerable value or above average risks. Businessmen will be able to take advantage of the more favorable insurance rates on sprinklered buildings and use the considerable savings to expand their businesses and contribute to the growth of the community.
Suitable for residences
To extend this philosophy, it is logical to consider those occupancies where we pay the highest costs for accidental fires—dwellings. Each year the majority of the 7500 persons who lose their lives in fires do so in dwelling fires. The open stair design, combustible building materials, large accumulations of combustibles and an increasing amount of plastic materials in homes make sprinkler protection for dwellings a must. The generally lower water requirements for an on-off sprinkler system lead us to the conclusion that the domestic water supply would be ideal for residential sprinklers. There is virtually no added expense beyond a few off-and-on heads and a small amount of material and labor.
In time, I am confident, reduced insurance rates would be more than adequate to amortize the cost of residential sprinkler systems to preserve our lives and resources. The fire service, which will benefit by reduced exposure to serious fires, will have to become involved in a program to overcome some of the code requirements for connections to domestic water supplies that discourage or prohibit the installation of automatic sprinkler systems in homes.
The installation of on-off sprinkler systems will reduce the number of serious fires that fire fighters encounter and thereby reduce the risks involved in a hazardous profession.
Advantage for chief
The on-off systems will provide other advantages. Upon arrival at a fire where one or more heads have operated, the officer in command does not have to be as concerned about the prompt closing of the sprinkler floor control valve since only those heads that are still extinguishing fire should be open. The on-off heads reduce the risk of closing a valve only to find that the fire is not under control and that an aggressive attack under unfavorable conditions must be initiated or that the sprinkler valve must be reopened until conditions improve.
Now the heads that are controlling or extinguishing the fire can be allowed to continue to operate with the least amount of water damage until the officer in command has an opportunity to investigate the status of the fire, st retch a charged line and determine the most appropriate tactic to control the situation. The pressure on the officer is reduced as well as the possibility of making a wrong decision.
The on-off sprinkler head also should relieve the tension a chief experiences when a water flow alarm indicates activation of the sprinkler system but an inadequate annunciator panel makes it impossible to pinpoint the fire location. As the chief tries to locate the flowing head as quickly as possible, he is put in the difficult position of weighing the damage that will be done by forcible entry against the water damage caused by the flowing sprinkler head. A chief can operate in a more deliberate and effective manner when he knows that an on-off head will cease flowing water when it is no longer needed.
How head functions
The on-off sprinkler head is controlled by a simple energy cell that converts thermal energy into mechanical energy. The cell opens the sprinkler head when a large amount of thermal energy is present and closes it when water reduces the thermal energy by extinguishing the fire.
The heart of the unit is a rectangular cylinder that protrudes from the circular disk above the conventional sprinkler head. The cylinder contains a hydrocarbon wax with a high coefficient of expansion which expands when heated and creates a pressure in the space surrounding the wax. Within this space there is a small piston in a rubber sleeve. As the pressure increases, it pinches the rubber sleeve and causes the piston to exert a horizontal thrust against a concentric cam in the half-inch disk to which the cylinder is attached. The cam is held in place over the waterway by a spring. As the temperature increases enough energy is transferred to force the cam against the spring, allowing water to flow.
As the fire is quenched and the temperature is reduced, the wax cools and retracts. This relieves the pressure on the rubber sleeve and allows the piston to resume its original position. The cam then rotates over the waterway and stops the discharge of water.
The energy cell, which activates at 125°F, has no degradable parts and is programmed to have water available for discharge long before 165°F is reached for sprinkler head operation. Two O rings at the waterway-cam interface ensure a leak-free closing and, in conjunction with a conventional sprinkler strut, provide double protection against accidental leakage.
The on-off mechanism also provides protection against accidental water discharge when, due to mechanical damage, the sprinkler head mechanism is displaced. With conventional heads, these accidents have caused considerable water damage.
The on-off heads are compatible with existing sprinkler systems and can be retrofitted by simply replacing the conventional heads.
THE AUTHOR: John T. O’Hagan is a former New York City fire commissioner and chief of department.
