Standpipe and Sprinkler Operations
All material for this series of articles is taken from the Nassau County, N. Y., Fire Training Manual. Prepared by Battalion Chief Thomas D. Ryan, FDNY (ret.), it is produced here through the courtesy of the Nassau County Vocational and Educational Extension Board, Charles R. Wallendorf, director; James C. Rogers, chief fire training instructor.
BESIDES the post indicator and O.S. & Y. valves which normally control the flow of water in a sprinkler system, two special types of valves are found in automatic systems. Dry pipe systems are quite similar to wet pipe systems with the exception that, in the former, the lines are kept full of air until a head opens. The dry pipe valve (Figure 27) is then operated, charging the entire system with water and sounding a local alarm or in some cases transmitting the alarm to a supervisory service which then notifies the fire department. In some occupancies (schools, hospitals, etc.) the alarm is directly transmitted to the fire department. Details of a typical drv pipe installation arc shown in Figure 28.
The dry pipe valve is designed so that, in the normal position, the valve will hold a clapper or seat (D) open.
The water then rushes into the sprinkler system and out the sprinkler head. At the same time it passes into the outlets at (L) and (M), actuating the alarm device and accelerator or exhauster.
When fire conditions indicate the system should be shut down, the supply may be closed off at an individual O.S. & Y. valve on an individual floor or at the main valve shown in the open position (stem out). In this latter move, the drain valve should be opened so that the remaining water in the system beyond the valve will not have to be discharged and possibly cause additional water damage. Fire fighters may then work in comfort under the opened heads. Before the main supply valve is again opened, the drain valve must be closed, the dry pipe valve reset, air pressure built up in the system by the compressor and the alarm system drained and placed once more in its normal position ready to operate.
One objection to the use of a dry pipe system is the loss of time between the opening of a sprinkler head and the issuance of water, an interval made necessary to permit the escape of the compressed air content of the sprinkler pipes. The problem is overcome by the installation of quickopening devices and by proper attention to the maintenance of these devices. There are two general types, accelerators and exhausters. In the first type, when a sprinkler opens and air pressure drops 1 or 2 pounds, the diaphragm (F) (figure 27) becomes unbalanced. This forces open a valve which permits the air pressure in the system to enter the intermediate chamber of the differential valve, and the valve trips. In the exhauster type, the diaphragm causes a larger valve to open and the air in the system discharges to atmosphere through an outlet. Air pressure in the system is thus reduced until the dry pipe valve itself trips.
Both dry and wet pipe systems are commonly equipped with means of sounding an alarm upon the opening of a head and the flow of water past the valve proper. One type employs a flexible vane or paddle in the waterway which activates a water motor gong on the outside of the building. Other types sound an electric gong inside the building when water pressure actuates an electric switch at the alarm valve (Figure 29). Some installations employ both types and also notify a supervisory agency, such as ADT or other service.
The water pressure from public mains is variable and so it becomes necessary to provide means of counteracting the effects of water hammer and momentary surges in water pressure to prevent the transmission of false alarms. Retard devices are installed between the alarm check valve and the water motor gong or pressure switch (Figure 30). By such means, in cases of momentary surges, the action of the water is retarded for several seconds to provide time for the clapper of the alarm check valve (Figure 29) to reseat and cut off the water from reaching the alarm activator. This necessary time interval in many cases prevents the alarm being sounded due to a common water main fluctuation.
If a fire actually opens one or more sprinkler heads, the flow of water lifts the main clapper off its seat and opens the auxiliary valve so that water quickly fills the retard chamber and contacts the electric circuit closer, sending the alarm to the office, throughout the building or to distant points. At the same time, the water may activate the water motor gong and sound the alarm inside or outside the building.
Automatic sprinklers have various temperature ratings which approximate the temperatures at which they will operate in a heated atmosphere. Where high heats are maintained, such as over boilers, over ovens and in drying rooms, a higher degree head must be used than in an ordinary occupancy. If high-degree heads are used where not required, i.e., in an ordinary atmosphere, the value of the sprinkler protection is materially reduced. The difference between the various heads, as to their ratings, is not only indicated on them but they may also be identified by colors. The table lists the ratings of the various heads, operating temperatures and distinctive colors. All heads which fuse at a fire should be replaced by those of duplicate ratings. If responding units do not have replacement heads, such can usually be procured from the owner or building superintendent.
Sprinkler heads are made of metal, screwed into the piping at standard intervals and generally have a ½-inch opening. The disc or seat of the sprinkler head is held in place (preventing the escape of water) by a strut or two levers inserted between the seat and the top of the yoke. Most frequently the strut is of metal, consisting of two or more pieces held together with fusible solder (Figure 31). Many types, however, use as a strut a quartz bulb which expands and breaks under heat or a solid chemical held in a cylinder which disintegrates by heat action.
When constructed, the struts or levers are set in place under compression and are released when the fusible device operates from the heat of the fire. The disc is released from the ⅛inch openings and water flows out under pressure. The force of the water against the deflector of the head breaks it into a heavy spray, part of which passes through the openings in the deflector to hit the ceiling and part is deflected downward.
To find a sprinkler control valve and to close it may take considerable time. If the fused heads are few in number, they may be closed by using a pole shut-off, sprinkler tongs (Figure 32), or a wooden wedge inserted in the ruptured head.
Discharges and head pressures
The exact amount of water being discharged from a system depends on the number of heads open, the type of head, and the pressures maintained on them. For most systems approximate discharges may be calculated by the following method:
Discharge in gallons per minute 1/2 the pressure in pounds at the head + 15.
The following table presents discharges at pressures up to 100 pounds at the head:
Based on the above, it may be seen that a 1,000-gpm pumper can effectively supply at most 50 heads at a minimum pressure of 15 pounds. A 750-gpm pumper can only supply about 35 heads. Each head will effectively cover 80 to 100 square feet of floor area.
Recommended engine pressures
Exact computations of engine pressures are impractical on the fire ground, due to required information on such factors as the number and type of heads opened, and the number, length and size oi the supply lines to the Siamese. In cases where the pumper is located near the fire building, most authorities recommend a pump pressure of 100 pounds be maintained, particularly on older systems, where there is always the danger of part of the system bursting if excessive pressures are built up on the pumper.
Supplying Siamese connection
The recommended number of supply lines and the method of hooking up to a Siamese is the same for both systems (see Figure 16, July 1963 issue of FIRE ENGINEEIUNG). If the system is automatic and already charged from another source (gravity tank, pressure tank, fire pump or connection to a public main), the pressure on the pumper side of the check valve in the Siamese connection (Figure 26, August 1963 issue of Fire Engineering) must exceed the pressure on the other side before the check will swing open and allow the pumper to actually feed the standpipe or sprinkler system. This also means that the engine pressure must he sufficient to close the check valve beneath the gravity tank on the roof, or on the discharge side of the pressure tank, fire pump, or street main. It is important that a pumper actually discharge some water and not pump continually against a closed check valve. In such cases the water in the pump will heat up considerably and possibly damage the packing or other parts of the pump. As such, this water is unsuitable for auxiliary cooling purposes, with the result that the oil in the engine may heat up to the point where the motor may burn out. A simple solution to this problem is to keep a bleeder valve (drain) open on one of the discharge gates so that a small stream of water spills to the ground and insures complete circulation.
- Whether or not the check valve beyond the Siamese connection is actually open in a standpipe or sprinkler system may readily be determined by the following method:
- Working with caution, slowly close or partially close the discharge gate(s) of the pumper supplying the Siamese. If the check valve is open (pumper actually supplying the water), the engine pressure on a positive-displacement pumper will go up, the motor will start to labor and slow down, and the relief valve will open.
- On a centrifugal pumper under the same conditions, the engine pressure will rise slightly until the relief valve opens and the passage of water through it can be heard. The engine speed will also start to increase (load partially or completely off it) to the point where the motor governor controls it.
- In addition, on both types if the water output is considerable, the intake gage on the pumper will show an increase in intake pressure as gate(s) are closed.
- If either type pumper is not actually putting water into the system (check closed), there will be no change in pump pressure or motor speed when the gate is closed.
- In addition to the method of calculating engine pressures required in standpipe operations, as explained previously, some authorities recommend this method which is adequate for most operations in which supply lines to the Siamese are short and a solid stream type of nozzle is used on the line: Required engine pressure = 100 pounds + 5 pounds per story.
- In standpipe operations where riser water supply is from a gravity tank or a weak water main, it is inadvisable to use l 1/2-inch lines or fog nozzles on floors immediately below the roof as the pressure on the riser outlet will not be sufficient to overcome friction losses in the small hose nor give required pressure on fog nozzles.
Studies of large-loss fires in sprinkler-protected buildings show that fire departments should follow the suggestions below to most effectively use sprinkler systems as a fire control and extinguishment tool:
- Fire departments should have a list of all sprinkler-protected buildings in the area which they protect. Each officer should be familiar with at least those buildings in his district to which he responds on first alarms.
- Sketches should be prepared showing the locations of alarm valves, control valves and fire department connections. Officers should be familiar with this data on buildings in their district.
- Fire departments should have information on the available water supply such as: How many pumpers can be used in addition to those supplying the fire department sprinkler connections; is there a water supply separate from that supplying the sprinkler system that can be used; is there a nearby surface water supply, such as a pond, from which pumpers can draft water?
- Fire department connections for sprinkler and standpipe systems should be inspected at regular intervals by the fire department to assure that caps can be readily removed, that threads are in good condition, and that the connection is otherwise ready for use and threads match those of the fire department.
- One of the first-alarm engine companies responding to a fire in a sprinkler-protected building should stretch two 2 ½-inch lines to the fire department connection.
- Fire departments should impress responsible personnel of sprinkler-protected buildings that once sprinklers have operated as a result of fire, the system should not be shut off before the fire department arrives.
- Extreme caution should be exercised by officers when ordering sprinkler systems shut off. A shut-off should be made only after a thorough check reveals the fire is out and will not rekindle. The fireman ordered to close the control valve should remain at the valve so that it can be opened without delay if needed.
When a shut-off is made by the fire department, someone should be left at the valve until the sprinklers can be replaced and the water supply restored. If the system cannot be put back into service, watch service should be maintained on each floor, in addition to the man at the control valve, until all danger is past.