19.1 Commentary

Single Stage Fire Alarm:

Suitable for small, simple buildings.
A single alarm signal prompts immediate evacuation of all occupants.

Staged Fire Alarm:

Appropriate for large and high-rise buildings.
Initial warning limited to certain areas or personnel, extending in stages to all occupants.

Scenarios for Staged Alarm:

Large/high-rise buildings: Evacuate areas closest and immediately above the fire first (phased evacuation).
Leisure complexes, shopping centers: Horizontal evacuation to a safe area within the building.
Hospitals: Progressive horizontal evacuation to adjacent fire compartments.
False alarms: Initial alarm restricted to staff for investigation before general evacuation.
Public buildings: Initial staff warning to avoid public panic, managed via a voice alarm system.
Industrial complexes: No need for evacuation in distant areas not affected by the fire.

Alarm System Features:

Two-stage alarm: "Alert" signal for areas not immediately affected, "Evacuate" signal for areas needing immediate evacuation.
Three-stage alarm: Staff alarm, "Alert" signal, and "Evacuate" signal.
Alarm systems should be designed based on formulated fire and evacuation procedures.
Division of buildings into alarm zones may be necessary to facilitate staged alarms.

Additional Facilities:

Voice alarm systems (BS 5839-8).
Emergency voice communication systems (BS 5839-9).

Inner Room Safety:

Smoke detectors in access rooms to warn occupants of inner rooms about potential fire hazards.

19.2 Recommendations

19.2.1 Recommendations applicable to all staged alarm systems

In multi-storey buildings with phased evacuation, if stairway capacity is inadequate to support a simultaneous evacuation of all floors, no single control should cause an “Evacuate” signal to be given throughout the building; a separate “Evacuate” control should be provided for each alarm zone.

NOTE In some buildings, a two-phase evacuation arrangement is used; the area of fire origin is evacuated first and the remainder of the building is evacuated simultaneously as a second phase. 19.2.1 does not apply to such situations, as adequate stairway capacity exists to evacuate the entire building in one phase.

19.2.2 Recommendations applicable to staff alarms

The following recommendations are applicable.

1. Use of Staff Alarms:

● Staff alarms should be used only if staff are adequately trained and numerous enough to handle fire situations.

● In residential care, the fire and rescue service must be summoned immediately when the staff alarm activates, though general alarm signals may have a delay.

2. Triggering of Staff Alarms:

● Typically activated by automatic fire detectors, not manual call points or other devices, unless in cases of frequent false alarms.

● Manual call points might be used cautiously to initiate staff alarms with proper indication and warning systems.

3. Visual and Audible Alarms:

● Visual staff alarms must conform to specified standards.

● Audible fire warnings must be provided in all areas of premises with a staff alarm system.

4. Transition and Detection:

● Staff alarms should transition to audible fire warnings after a preset time (usually within six minutes) or if a second detector activates (coincidence detection).

● The full alarm may be triggered by a second detector in the same or different area.

Inner Room Safety:

● Smoke detectors in access rooms must alert occupants of inner rooms immediately if they are the only escape route, unless visibility is clear between the rooms.

Figure 5 — Typical staff alarm arrangement

Screenshot (10).png

Inner Room Safety:

Smoke detectors in access rooms must alert occupants of inner rooms immediately if they are the only escape route, unless visibility is clear between the rooms.

19.2.3 Recommendations applicable to audible “Alert” signals

The following recommendations are applicable.

Audible Alert Signal:

Should be intermittent with 1 ±0.5 seconds on and off.

Synchronization:

Signals from different fire alarm devices must be synchronized to avoid confusion between "Alert" and continuous "Evacuate" signals.

Signal Change:

Manual and possibly automatic provisions should allow changing from "Alert" to "Evacuate" signals in any area.

Automatic Cessation:

The "Alert" signal may automatically cease after 30 seconds, but should reoccur for at least 10 seconds every three minutes until manually silenced.

19 Staged fire alarms