Sprinkler systems are one of the most important fire protection tools in use today. Monitoring these systems is not only wise, but in most cases it is required by code.
“Of the 41 structures involved in large-loss fires in 2003, only 12 were equipped with automatic suppression equipment. Twenty-two definitely had no automatic suppression equipment ... ” (Large-Loss Fires for 2003, NFPA Journal, November/December 2004).
Also, according to the U.S. Fire Administration, not a single life has been lost by a fire in residences equipped with a fire sprinkler system.
Although fire technicians may not be charged with the installation of fire sprinkler systems, it is their job to monitor them, both locally and remotely. This is accomplished through the use of control valve tampers, waterflow pressure and flow switches, as well as low/high air pressure switches.
Understanding 4 Sprinkler Types
There are four general types of sprinkler systems in use today. They are wet-pipe, dry-pipe, preaction and deluge. In order to most effectively monitor them, technicians should have a good understanding of how each one works.
Wet-type sprinkler systems operate so all branch pipes are pressurized with water at all times. When the fusible link in a sprinkler head melts due to heat, the head opens up and water flows.
Dry-pipe systems operate so all branch pipes are pressurized with air and not water. Water is prevented from entering until it is required. Dry systems are used in environments where freezing is likely.
“A dry pipe system should be installed only where heat is not adequate to prevent freezing of water in all or parts of, or in sections of, the system” (Section A-7.2, NFPA 13, Sprinkler Systems, 2002 Edition).
In this type of sprinkler system, air is pumped into the system by an air compressor whose job it is to maintain a 6:1 ratio between water and air pressure.
The air pressure is designed to maintain the closed condition of a positive-latching clapper valve contained inside the dry pipe valve assembly. The clapper remains closed as long as this ratio is maintained.
When a fusible link in a sprinkler head melts, the sprinkler head opens. This causes the air pressure to drop so the water pressure will open the clapper valve, allowing water to fill the sprinkler system.
As a side note, attachments added to a sprinkler system — such as an air compressor — must be listed for the intended use. Also, according to Section 3-1.3, NFPA 13, Sprinkler Systems, 2002 Edition, wet systems are allowed to provide water to dry-, preaction-, and deluge-type fire sprinklers.
Preaction sprinklers are similar to dry-type in that the branch pipes are filled with air. In addition, they use electrically or pneumatically activated valves that allow water to flow in the system.
Operation of the valve can be through detectors or a sprinkler system. A releasing control panel may also be used. In this case, water is prevented from filling the branch pipes until an event occurs, such as the activation of a heat or smoke detector or the melting of a fusible link in a sprinkler head.
Once detection occurs, water is permitted to fill the pipes. But, until one of the sprinkler heads is activated by heat, water is not released into the environment.
Deluge systems are similar in operation to the preaction type, but the sprinkler heads are open and ready to facilitate the immediate flow of water in protected areas. Once the air pressure rapidly drops, the release valve is opened to allow water to flow through the branch pipes and out of the already open sprinkler heads.
Monitoring Water Flow/Air Pressure Installing water-flow and supervisory devices in sprinkler systems requires a good bit of code knowledge. For example, according to National Fire Alarm Code, NFPA 72, an alarm signal must ensue within 90 seconds of water-flow detection.
Also, according to Section 3-18.104.22.168.2, the number of water-flow devices that can be installed on a single initiating circuit is five. Of course, fire technicians can install more than five flow devices using additional initiating zones.
The use of a listed outdoor notification appliance is also required, unless the sprinkler system is part of a “central station, auxiliary, remote station or proprietary signaling fire alarm system utilizing listed audible inside alarm devices” (Section A.22.214.171.124, NFPA 13, 2002).
In wet sprinkler systems, water-flow detection usually is performed through the use of a vane-type flow switch. This arrangement is only permitted in wet-type sprinkler systems per Section 126.96.36.199 of NFPA 13, 2002 Edition. In addition, fire technicians can achieve the same detection using a pressure switch (see illustration on page 36 of March issue).
Although fire technicians do not usually install vane and pressure switches themselves, it is their job to monitor them.
Supervision Assures Operation
Supervision is another important element in fire sprinkler monitoring. Supervisory devices, such as shutoff tamper switches, high/low pressure switches, and pressure- and vane-type flow switches, are designed to provide early warning of off-normal conditions that occur in a sprinkler system. Examples include main water valves in dry- and wet-type sprinkler systems as well as high-low pressure switches in dry- and preaction-type systems.
NFPA 72, Section 3-8.3.3, 1999, addresses this issue: “The provisions of 3-8.3.3 shall apply to the monitoring of sprinkler systems, other fire suppression systems, and other systems for the protection of life and property for the initiation of a supervisory signal indicating an off-normal condition that could adversely affect the performance of the system.”
In this regard, control valves must be supervised for physical movement. According to Section 2-9.1.1, NFPA 72, 1999, an off-normal supervisory signal must occur when a control valve is turned two revolutions, or one-fifth of the valve’s normal travel.
In all cases, two distinctly different supervisory tones must occur; one for off-normal and the other when the valve returns to its normal position. The same holds true for air pressure switches and other supervisory devices.