Positive Alarm Sequence and Presignal Systems
Positive alarm sequence and presignal systems delay occupant notification to allow time for investigation of a fire. While both systems delay occupant notification, the function of the features and where they are permitted are different.
Presignal systems sound an alarm signal in constantly attended location (control room, fire brigade station, etc.) when the initial fire alarm signal is received. Where the system is connected to a remote location or supervising station, the alarm signal is sent immediately upon activation of the initial alarm signal. System operation of a presignal system to provide occupant notification requires human action. A feature that allows the control equipment to delay the general alarm by more than one minute after the start of alarm processing is also permitted.
A common application of presignal systems is detention applications. In detention applications, automatic and immediate activation of the fire alarm system notification appliances is typically undesirable. Since most building occupants in a detention occupancy are incapable of self-evacuation, a fire alarm activation could result in an unnecessary panic.
Manual activation of the fire alarm system typically is accomplished by a pull station located in a secured area (like the constantly attended location) or using a key-operated pull station.
Positive alarm sequence systems also sound an alarm in a constantly attended location when an automatic detector selected for positive alarm sequence. Positive alarm sequence also requires acknowledge of the signal within 15 seconds by trained personnel to prevent occupant notification. Once the signal has been acknowledged, the trained personnel have 180 seconds to investigate the fire condition and reset the system. If the system is not reset during the investigation phase, occupant notification occurs automatically. Additionally, if a second automatic detector is activated during the investigation occupant notification occurs automatically. If any other initiating device is activated, the system automatically triggers occupant notification automatically. Signals are sent to the supervising station when occupant notification occurs.
A common application for presignal systems is hotels. While hotel occupants are generally capable of self-evacuation, false alarms can be problematic. In addition to long evacuation times for large occupant load buildings, there is also the tendency to think a fire alarm is the system “crying wolf”, especially if the activation occurs during late evening and early morning hours.
IBC and NFPA 101
According to NFPA 72, both presignal and positive alarm sequence require AHJ approval. NFPA 101 (Life Safety Code) and IBC (International Building Code) further address these systems.
NFPA 101 permits positive alarm sequence in all occupancy classifications, but only permits presignal in existing occupancy classifications, with both requiring AHJ approval. The IBC does not specifically address positive alarm sequence, and requires fire code official and fire department approval for the use of presignal.