What question is your article answering?Fire alarm zones explained (detection zones and alarm zones)
Fire alarm zones explained: the difference between a detection zone (where a fire is detected) and an alarm zone (where the alarm sounds), defined by a competent designer per BS 5839-1.
Direct answer
A fire alarm zone is a defined area of a building used to indicate where a fire has been detected so that people can be located and directed quickly. BS 5839-1 distinguishes a detection zone (the area covered by a group of detectors/call points shown as one location on the panel) from an alarm zone (the area within which the alarm signal is broadcast, used in phased or staged evacuation). The exact rules — such as maximum zone area, search distance and how zones relate to building layout — must be taken from the current BS 5839-1 and applied by a competent designer; this article explains the concept, not the limits.
Applies to
- Products / Models: Not applicable (a system design concept)
- Firmware / Version: Not applicable
- Region: UK
- Standards: BS 5839-1 (zoning)
Why buildings are divided into zones
- When the panel signals a fire, staff and the fire service need to find the source quickly. Zones narrow the search to a defined area.
- On a conventional system the zone is what the panel can indicate; on an addressable system the panel can indicate the individual device, but zones are still defined for clear, consistent indication and for the building plan.
Detection zone vs alarm zone
- Detection zone — the geographical area monitored by a group of detectors and manual call points that the panel reports together as one location. It answers "where has something been detected?".
- Alarm zone — the area within which the alarm warning is given. In a simple building the whole building is one alarm zone; in larger or phased-evacuation buildings the building is divided so that some areas are alerted before others. It answers "where is the alarm being sounded?".
- A detection zone and an alarm zone are not always the same area; how they are defined is a design decision.
How zones are defined
- A competent designer defines the zones from the building layout, its use and the evacuation strategy, in line with the current BS 5839-1.
- BS 5839-1 places limits on things such as the size of a detection zone and how far someone should have to travel to confirm the source; the precise figures must come from the standard, not from a general article.
- The zone plan is documented (often as a zone chart displayed at the panel) and confirmed at commissioning and handover — see Fire alarm commissioning and handover: what to expect.
Zones and the system category
- Zoning works alongside the system category (what the system is designed to protect and how much of the building it covers) — see Fire alarm system categories explained (BS 5839-1: L, P and M).
- Changing the building layout or use can change both the zoning and the category; review them together with a competent person.
When to contact technical support
- If you need to understand how your Hochiki panel indicates zones or how many zones it supports.
- If a building change means the zone plan may need revising — this requires a competent designer, not a general article.
Safety note
This article is general guidance for Hochiki Europe products. Installation, commissioning, maintenance and modification of fire detection and alarm systems must be carried out by a competent person in accordance with the applicable standards (for example BS 5839-1 in the UK) and the requirements of the relevant authority having jurisdiction. Always refer to the current product manual and data sheet for the exact model before carrying out any work.
References
- BS 5839-1 (current edition) — detection zones, alarm zones and zoning recommendations
- The system's zone plan / zone chart
Last reviewed: 2026-06-16 — Reviewed by: Takashi Ishikawa