Fire Protection Systems PDF

Fire Protection Systems • Chapter 15 ^ OBJECTIVE 4 Describe the wet pipe, dry pipe, preaction, and deluge designs for sprinkler systems. TYPES OF SPRINKLER SYSTEMS The NFPA 13 Standard for the Installation of Sprinkler Systems is the fundamental document that governs the design and installation c...

Fire Protection Systems • Chapter 15 ^ OBJECTIVE 4 Describe the wet pipe, dry pipe, preaction, and deluge designs for sprinkler systems. TYPES OF SPRINKLER SYSTEMS The NFPA 13 Standard for the Installation of Sprinkler Systems is the fundamental document that governs the design and installation criteria for sprinkler systems. This standard does not mandate when a sprinkler system is needed; that is the function ofNFPA-101 (Life Safety Code) or a specific building code. There are five types of sprinkler systems defined in NFPA-13. • Wet pipe sprinkler system • Dry pipe sprinkler system • Preaction sprinkler system • Combination of dry pipe and preaction systems • Deluge sprinkler system 1. Wet Pipe Systems The wet pipe system (shown in Figure 15) is the most common system, the easiest to design, and the simplest to maintain. This system contains water under pressure at all times by an open valve (8) and uses a series of closed sprinklers. When a fire occurs and produces enough heat to activate one or more sprinklers (9), the water will discharge immediately from any of the activated sprinklers. To prevent freezing, the wet pipe design should only be used when the temperature of the protected area is maintained at or above 4°C. This system is typically found in office buildings, stores, manufacturing facilities, hotels, and health care facilities. Figure 15 - Wet Pipe Sprinkler System 1. Main water supply 6. Check valve 2. Main drain connection 7. Alarm valve 3. Fire department connection 8. Water supply gate valve 4. Water flow alarm 9. Automatic sprinklers 5. Water pressurized distribution piping 10. Inspectors test connection 3rd Class Edition 3 • Part A2 791 p. Chapter 15 • Fire Protection Systems 2. Dry Pipe Systems The dry pipe system is shown in Figure 16. This design is used in environments where the temperature could become less than 4°C. The piping normally contains air under pressure (5) at 275 kPa maximum. A dry-pipe valve is used to block the water supply and to act as the interface between the water and air (6). The valve operates on a pressure differential principle, with the surface area of the valve face on the air side being greater than the surface area on the water side. The difference in surface area keeps the valve closed. When a fire occurs and enough heat is generated, one or more sprinklers (9) will activate and open. System air will then escape through the open sprinklers, dropping the pressure on the air side of the dry pipe valve. At a predetermined pressure differential, the dry pipe valve (6) will open and water will be supplied into the piping. The pipe network will fill and water will discharge from any open sprinklers. Dry pipe systems are more complex than wet pipe systems. They require a reliable air source and involve specific design limitations, such as the volume of pipe that can be governed by one dry pipe valve, plus special adjustments that are necessary for the anticipated area of operation. Figure 16 - Dry Pipe Sprinkler System 1. Main water supply 6. Dry pipe valve 2. Main drain connection 7. Check valve 3. Fire department connection 8. Water supply gate valve 4. Water flow alarm 9. Automatic sprinklers 5. Air pressurized distribution piping 10. Inspectors test connection 3. Preaction Systems The piping for a preaction system is shown in Figure 17. This system is typically provided with a minimal amount of air pressure, with no water in it, under normal circumstances. The water supply (2) is blocked by a preaction valve (3), which is normally closed. The system is equipped with a supplemental detection system (11), which signals the preaction valve to automatically open when a fire is detected and admit water into the pipe network. However, water will not discharge from the system until a fire has generated a sufficient quantity of heat to activate one or more sprinklers. In essence, the system becomes a wet pipe system once the preaction valve opens. The small amount of air maintained in the pipe is used to monitor the integrity of the pipe. If a leak develops, the air pressure wiU drop (10) and an alarm will sound. 792 3rd Class Edition 3' Part A2 Fire Protection Systems • Chapter 15 f& Preaction systems are typically found in environments that house computer equipment or communication equipment, museums, and other facilities where inadvertent water discharge must be avoided. Figure 17 - Preaction Sprinkler System D^-^-^a 1. Main water supply 8. Low pressure supervisory panel la. Control water supply 9. Solenoid valve 2. Water supply gate valve 10. Supervisory low-pressure alarm 3. Control (preaction) valve 11. Heat detectors 4. Pressure alarm switch 12. Release panel 5. Check valve 13. Fire alarm bell 6. Water motor alarm 14. Trouble horn 7. Manual control station 15. Automatic sprinklers 4. Combination of Dry Pipe and Preaction The combination system has characteristics of both the preaction and dry-pipe systems. Before water can be admitted into the piping, the detection system must activate and the fire must generate enough heat to cause one or more sprinklers to open. WTien one or more sprinklers open, the air pressure will drop and the preaction valve will open. In the combination system, the pressurized air is the primary means of system activation. The system is often referred to as a double-interlock preaction system. This system is common in deep-freeze facilities where accidental preaction valve opening would cause frozen water pipes in a very short time. 5. Deluge Systems Rapidly growing and spreading fires are most effectively contained with a deluge system, such as the one shown in Figure 18. These systems are intended to deliver large quantities of water over a large area in a relatively short period of time. The sprinklers in a deluge system have their restricting elements removed to allow for a large volume stream, as opposed to a sprinkling pattern. A deluge valve (3) blocks the system water supply. In larger systems, there may be several deluge valves, each dedicated to one or more sprinklers or nozzles (12). Each sprinkler or nozzle serves a specific area or piece of equipment. The piping located downstream of a deluge valve is at atmospheric pressure with the sprinklers constantly open. Water supply pressure is maintained up to the deluge valve or valves. In a similar manner to the preaction system, a fire detection system (8) is provided throughout the same area as the sprinklers. Upon detection of a fire, deluge valves are automatically opened, thereby admitting water into the pipe network and to the nozzles. 3rd Class Edition 3 • Part A2 793 ,s> Chapter 15 • Fire Protection Systems The deluge system is common for facilities that contain combustible or flammable liquids. A typical example is process vessels and storage tanks for hydrocarbon products, such as propane. The large volumes of water not only provide some firefighting capabilities, but are often more important for their cooling action. This cooling may prevent thermal damage that would otherwise occur very quickly. Figure 18 - Deluge Sprinkler System ® 1. Main water supply 7. Solenoid valve la. Control water supply 8. Heat detectors 2. Water supply gate valve 9. Deluge Release Panel 3. Control valve 10. Fire Alarm Bell 4. Pressure alarm switch 11. Trouble horn 5. Water motor alarm 12. Open sprinklers 6. Manual control station Note: There are several variations to each of the basic systems. Antifreeze systems, for example, are basically wet-pipe systems with a certain percentage ofantifreeze added to lower the freezing point. This type of system can be used to protect small areas, such as the areas that may be found at outside loading docks or exterior canopies. NFPA-13 specifies select types of antifreeze concentrate and percentages for these systems. 794 3rd Class Edition 3 • Part A2