Why Is Correct Fire Alarm Detector Placement Important?

Automatic fire detectors are designed to identify signs of fire and send a signal to the fire alarm control panel. However, smoke and heat must reach the detector before it can respond.

Consequently, a detector placed in a dead-air space, directly beside an air-conditioning outlet or behind a large obstruction may react later than expected. In some circumstances, the unsuitable location may also increase the risk of unwanted fire alarms.

Correct detector positioning helps to:

• Provide the earliest practical warning of fire.
• Support safe evacuation from the building.
• Reduce unwanted and false alarms.
• Provide suitable coverage throughout the protected area.
• Support compliance with the agreed fire alarm system category.
• Protect people, property and business operations.
• Ensure detectors remain accessible for testing and maintenance.

Importantly, detector placement should be based on the building’s fire risk assessment, fire strategy, system category, room use and physical layout.

What Standard Covers Fire Alarm Detector Positioning?

In UK non-domestic premises, fire alarm systems are generally designed, installed, commissioned and maintained in accordance with BS 5839-1:2025.

The standard covers commercial and other non-domestic buildings, including offices, shops, schools, warehouses, factories, hotels and care environments. It provides recommendations for system design, detector selection, installation, commissioning and ongoing maintenance.

Domestic premises are normally covered by a different part of the standard, BS 5839-6. Therefore, a domestic smoke alarm arrangement should not automatically be used as the design basis for a commercial fire alarm system.

Further information is available from the following authoritative sources:

• BSI: BS 5839-1:2025 for non-domestic premises
• Fire Industry Association: BS 5839 series
• UK Government: workplace fire risk assessments

Where Should Smoke Detectors Be Installed?

Smoke detectors are intended to detect airborne products of combustion. Because many fires produce smoke before a significant temperature increase occurs, smoke detection can provide earlier warning than heat detection in suitable environments.

Optical smoke detectors are commonly used for detecting slow-burning or smouldering fires. They are often suitable for escape routes and occupied rooms where smoke is not normally present.

Typical Locations for Smoke Detectors

Depending on the system category and fire risk assessment, smoke detectors may be appropriate in:

• Escape routes and corridors.
• Offices and meeting rooms.
• Reception areas.
• Classrooms and teaching spaces.
• Hotel bedrooms.
• Care home bedrooms and circulation spaces.
• Retail areas.
• Electrical rooms where environmental conditions are suitable.
• Storage rooms that are not excessively dusty.
• Plant areas where smoke, steam or dust is not normally present.

Nevertheless, the fact that an area appears suitable for smoke detection does not remove the need for a proper design assessment.

Where Smoke Detectors May Be Unsuitable

A standard smoke detector may cause unwanted alarms when installed in an environment where airborne particles, steam or fumes occur during normal activities.

Potentially unsuitable areas include:

• Commercial kitchens.
• Bathrooms and shower rooms.
• Areas containing significant steam.
• Dusty manufacturing processes.
• Vehicle workshops where exhaust fumes may be present.
• Loading bays exposed to external pollution.
• Rooms where aerosols or theatrical smoke are regularly used.

In these locations, a heat detector, multi-sensor detector or specialist detection system may be more appropriate. However, the final selection must be based on the required fire response and environmental conditions.

For a detailed comparison, read our guide to smoke detectors versus heat detectors.

Where Should Heat Detectors Be Installed?

Heat detectors react to changes in temperature rather than visible smoke particles. As a result, they are often selected for environments where smoke detectors would be vulnerable to contamination or unwanted alarms.

However, heat detection normally provides a slower warning than suitable smoke detection. Therefore, a heat detector should not be chosen simply because it appears more convenient.

Typical Locations for Heat Detectors

Heat detectors may be suitable for:

• Commercial kitchens.
• Boiler rooms.
• Plant rooms.
• Garages and vehicle workshops.
• Dusty industrial areas.
• Small storage areas affected by airborne dust.
• Laundry rooms with steam or moisture.
• Areas subject to normal cooking fumes.

Rate-of-Rise and Fixed-Temperature Heat Detectors

Different heat detector classes respond in different ways. For example, rate-of-rise detection responds to a rapid increase in temperature. Meanwhile, fixed-temperature detection operates when the sensing element reaches a predetermined temperature range.

The detector class must be suitable for the normal operating temperature of the room. Otherwise, everyday heat could cause an unwanted alarm, or the detector may not respond appropriately to a developing fire.

What Is the Correct Smoke and Heat Detector Spacing?

Detector spacing should be calculated during the design process. It should not be estimated by looking at the room or by placing one detector in the centre of every space without considering its dimensions.

For general ceiling-mounted point detection, the design commonly considers the maximum horizontal distance from any point in the protected area to the nearest detector.

These figures should not be treated as a universal centre-to-centre spacing rule. Room shape, ceiling construction and detector layout must be considered so that every relevant point remains within the permitted coverage.

Moreover, detector spacing may need to be reduced where there are: