What is the operational sequence following a fire event in a double-interlock pre-action sprinkler system?

The operational sequence following a fire event in a double-interlock pre-action sprinkler system is designed to prevent accidental water discharge while ensuring rapid fire suppression when needed. First, a fire detection event must occur. This is typically initiated by a separate fire detection system, such as smoke or heat detectors, within the protected area. This detection system is electrically interlocked with the pre-action valve. Second, the fire detection system must activate, sending a signal to the pre-action valve control panel. Third, the pre-action valve control panel verifies the alarm signal from the fire detection system. Unlike single-interlock systems, a double-interlock system requires two independent events to occur before water is released into the sprinkler piping. Fourth, after the fire detection system alarm is verified, the pre-action valve opens, allowing water to flow into the sprinkler piping network. However, water is still not discharged from the sprinkler heads at this point. Fifth, a sprinkler head must then activate due to the heat from the fire. The heat causes the thermal element in the sprinkler head to release, opening the sprinkler head. Sixth, once the sprinkler head opens, water is discharged onto the fire, suppressing the flames. The system is designed so that the fire must be confirmed both by the fire detection system and by the sprinkler head activation before water is discharged. This sequence minimizes the risk of accidental water damage due to false alarms or mechanical failures, while still providing effective fire protection. Double-interlock systems are often used in areas where water damage is a major concern, such as data centers or museums.