Zoning Requirements under BS 5839-1:2025

Overview

Under BS 5839-1:2025, zoning is a fundamental design principle of fire detection and fire alarm systems. Proper zoning ensures that:

• The location of a fire can be quickly identified
• Occupants can evacuate safely
• Fire & Rescue Service attendance is effective
• The fire strategy of the building is supported

Zoning is covered primarily in:

• Clause 12 - Fire Detection Zones
• Clause 13 - Alarm Zones

Zoning must always align with the evacuation strategy and system category (L or P category).

1. Fire Detection Zones (Clause 12)

Definition

A fire detection zone is:

A subdivision of the protected premises such that the occurrence of a fire within it is indicated separately from an indication in any other subdivision

In simple terms:

• Each zone must allow responders to narrow down the fire location.
• A fire signal must identify which part of the building is in alarm.

1.1 General Requirements

All fire detection zones must:

• Be clearly identifiable at the Control & Indicating Equipment (CIE)
• Correspond with a Zone Plan
• Be arranged to assist in locating the fire quickly
• Support safe evacuation and firefighting operations

1.2 Maximum Zone Size

Under BS 5839-1:

• A fire detection zone should not normally exceed 2,000 m²

• A single zone should not normally extend beyond:

  • More than one storey
  • Separate fire compartments (with some defined exceptions)

Storey Rule

Each storey should normally be treated as:

• A separate fire detection zone

Exceptions may apply where:

• The total floor area is small
• The building layout makes multi-storey zoning logical

1.3 Search Distance Requirement

The standard introduces the concept of search distance:

The distance a person must travel within a zone to determine the fire’s location

Search distance should not normally exceed:

• 60 metres

This ensures:

• Firefighters can rapidly identify the seat of fire
• Zones are not so large that location becomes impractical

1.4 Zoning in Non-Addressable Systems

For conventional (non-addressable) systems:

• Each zone corresponds to a physical circuit
• Automatic detectors and MCPs are grouped per zone
• The panel indicates only the zone, not the device

Therefore:

• Zone design is critical to minimise search time
• Larger buildings require more zones

1.5 Zoning in Addressable Systems

In addressable systems:

• Each detector has a unique address
• Exact device location is displayed

However:

⚠ Zoning is still required

Even with full addressability:

• The building must still be subdivided into fire detection zones
• Zones must still comply with maximum area and search distance rules
• A zone plan is still required

Addressability does not remove zoning obligations.

1.6 Manual Call Point (MCP) Only Zones

Where a zone contains only MCPs:

• It may exceed 2,000 m² in certain circumstances
• However, clarity of indication must still be maintained

2. Alarm Zones (Clause 13)

Definition

An alarm zone is:

A geographical subdivision of premises in which a fire alarm warning can be given separately and independently from other subdivisions

This relates to:

• Sounder circuits
• Phased evacuation
• Staged alarm systems

2.1 Relationship to Evacuation Strategy

Alarm zones must align with:

• Simultaneous evacuation strategy
• Phased evacuation strategy
• Staff alarm strategies
• Two-stage alarm systems

For example:

2.2 Independence of Alarm Zones

Where multiple alarm zones are used:

• A fault in one zone must not disable others
• Sounder circuits may need duplication in large open areas
• Zoning must prevent total loss of warning in critical spaces

3. Zone Plans (Clause 22.2.5)

BS 5839-1:2025 makes it clear that:

A Zone Plan must be provided where:

• There is more than one zone on any storey

The plan must:

• Be displayed adjacent to the CIE

• Clearly show:

  • Building layout
  • Zone boundaries
  • Zone numbers
  • Staircases
  • Final exits

Unacceptable Variation

Clause 6 explicitly states that:

The absence of a zone plan in premises with more than one zone per storey - particularly premises in which people sleep - is unacceptable

This is considered a serious life safety deficiency.

4. Zoning and System Categories

Zoning design must reflect system category:

Improper zoning can undermine:

• The life safety objective
• Fire engineering solutions
• Compartmentation strategies

5. Common Design Mistakes

❌ Over-Large Zones

Exceeding 2,000 m² or 60 m search distance.

❌ Multi-Storey Zones

Without justification.

❌ No Zone Plan

A serious non-compliance.

❌ Confusing Fire Detection Zones with Alarm Zones

They serve different purposes.

❌ Assuming Addressable Systems Remove Zoning Requirements

They do not.

6. Engineering Considerations (UK Practice)

In real-world UK installations:

• High-rise residential blocks typically zone per floor.
• Schools often zone per wing or floor.
• Hospitals require zoning aligned with progressive horizontal evacuation.
• Warehouses may require additional subdivision despite open plan.

Zoning should always be:

• Risk-based
• Strategy-driven
• Documented in design certificate
• Reflected in cause & effect programming

7. Zoning is a Design-Stage Responsibility

Fire detection zoning must be determined during the system design stage, not during installation or commissioning.

Under BS 5839-1:2025:

• System category must be defined before design begins (Clause 4)
• Responsibilities for design must be clearly documented (Clause 5)
• Variations must be formally recorded and justified (Clause 6)
• A formal Design Certificate is required (Annex G)

Because zoning affects:

• Compliance with maximum zone size
• Search distance
• Storey separation
• Cause & effect programming
• Alarm zoning
• Zone plan layout
• Fire strategy alignment

…it forms part of the core system design.

Design Certificate Implications

The Design Certificate confirms that:

• The system category has been correctly selected
• The protected areas are defined
• Zoning complies with BS 5839-1
• Any variations are declared

If zoning is not defined at design stage:

• The designer cannot legitimately sign the Design Certificate
• Responsibility becomes blurred
• Compliance is questionable
• Liability increases

Practical Engineering Note (UK Reality)

On many UK projects:

• Zoning is “worked out on site”
• Zone boundaries are adjusted after first fix
• The zone plan is drawn after commissioning

This approach is non-compliant.

The zone layout should be agreed and documented before installation begins.

Installation should follow the design, not determine it.

Best Practice

At design stage, the designer should produce:

• A zoning drawing
• Defined zone numbers
• Zone boundaries per storey
• Confirmation of zone sizes (m²)
• Confirmation of search distances
• Alarm zoning strategy
• Statement of compliance within the Design Certificate

8. Compliance Checklist

When reviewing a design:

• Does each zone comply with 2,000 m² limit?
• Is search distance ≤ 60 m?
• Is each storey separately zoned?
• Is a zone plan provided?
• Do alarm zones align with evacuation strategy?
• Are fault scenarios considered?

References

• BS 5839-1:2025 - Clause 12 (Fire detection zones)
• BS 5839-1:2025 - Clause 13 (Alarm zones)
• BS 5839-1:2025 - Clause 22.2.5 (Zone plans)
• BS 5839-1:2025 - Clause 6 (Unacceptable variations)