Undersized fire detection: what signs to look for?Undersized fire detection: what signs to look for?

How do I know if my fire detection system is undersized?

A fire detection system is undersized when its design no longer corresponds to the actual use of the building: rooms reallocated without revision of the detection, extensions not connected to the control panel, detectors installed for an activity that no longer exists. The gap develops gradually, often invisible until an incident or inspection reveals it. Identifying it requires systematically comparing the original installation plans, designed according to standard NBN S 21-100-1, with the current occupancy of the building. This comparison work is rarely done spontaneously: it is triggered by a change of tenant, an extension, or a periodic inspection report (NBN S 21-100-2) that identifies gaps. The following sections detail the concrete indicators to monitor.

What are the signs of an uncovered zone after room reallocation?

An uncovered zone is indicated by the absence of detectors in a room whose use has changed since the initial design of the installation: a former office converted into a storage room, a reserve transformed into a workshop, an open floor plan partitioned into several cells. The original detection plan remains aligned with the old configuration, while the fire risk has changed in nature.

Concrete signs to look for:

• partitions or repartitioning visible on site but absent from the detection plan;
• rooms with particular risk (storage, technical room, kitchen) without appropriate detector;
• detection zones that no longer correspond to the actual fire compartments of the building;
• a room permanently occupied by staff when it was originally classified as "infrequently used technical room".

This gap is corrected by a plan review, comparing the existing detector layout to the actual use observed on site, room by room.

How to identify a building extension not integrated into the fire detection system?

An extension not integrated into the fire detection system is recognized when the new rooms do not send any information to the existing control panel, or when they are covered by an autonomous installation disconnected from the rest of the building. This case is common after expansion work carried out by a different trade than the one responsible for detection.

Revealing indicators:

• visible detection cables that stop abruptly at the boundary of the old building;
• a control panel whose number of loops or zones displayed no longer corresponds to the actual exploited area;
• an NBN S 21-100-2 inspection report that mentions zones "outside controlled perimeter";
• an extension classified by the building as part of the same compartment, while detection treats it as a separate unit.

Bringing it up to standard involves integrating the extension into the same detection plan as the existing building, with verification of zoning consistency according to the Royal Decree of 7 July 1994.

What are the signs of poor detector positioning?

A poorly positioned detector is identified by a location that no longer corresponds to the actual configuration of the ceiling, furniture or room activity: a detector hidden by a mezzanine added later, a smoke detector installed above a deep fryer or battery charging area that should receive a heat detector, or a detector lost in a blind spot created by new layout.

Situations to monitor on site:

This identification work is ideally done during the periodic inspection visit, comparing the initial plan to the observed configuration.

What other alerts reveal a gap between installation and use?

Other signals, less visible than uncovered zones, also reveal a gap between the detection installation and the actual use of the building. They often appear in monitoring documents rather than on site itself.

• The maintenance register, required by NBN S 21-100-2, mentions repeated anomalies in the same zones without lasting corrective action.
• The number of people present in the building has increased significantly since the initial design of the installation, which changes evacuation criteria without the detection having been reviewed.
• The prevention advisor or the emergency zone (hulpverleningszone) issues remarks on the consistency between the evacuation plan and the detection plan during an opinion.
• The alarm control panel still displays zones designated by the name of a former activity, a sign that technical documentation has never been updated.

These administrative signals are just as revealing as a physical absence of detector: they indicate that documentary monitoring has not accompanied the building's transformations.

What approach should be adopted to bring the installation up to standard?

Bringing an undersized fire detection installation up to standard follows a structured approach, starting from documentary assessment to result in an adaptation validated by a competent body. It is not limited to adding detectors where they are visibly missing.

1. 1.Gather the original installation plans and compare them to the current building configuration, room by room.
2. 2.List the gaps identified during successive NBN S 21-100-2 inspections, particularly repeated untreated remarks.
3. 3.Have an assessment carried out by an installer familiar with standard NBN S 21-100-1, including extensions and reallocated zones.
4. 4.Establish an upgrade plan, prioritizing zones with particular risk and rooms with high occupancy.
5. 5.Have the extension or modification of the installation validated, ensuring that the equipment used benefits from BOSEC certification when applicable.
6. 6.Inform the competent emergency zone (hulpverleningszone) if the modification affects the general safety organization of the building.

This approach is part of the general obligations of the Code on Well-being at Work (Book III, Title 3), which requires the employer to maintain fire prevention measures adapted to the reality of operations, not just to the original building configuration.