Fire alarm: who is notified and in what order during activation?Fire alarm: who is notified and in what order during activation?

What exactly happens when a detector senses the start of a fire?

A smoke, heat or flame detector that senses an anomaly transmits a signal to the building's fire detection control panel, which displays what is called a restricted alarm. This first stage is not yet a general alarm: it is only visible at the signalling panel, usually located in a technical room or at reception, and is not yet communicated to occupants.

The NBN S21-100-1 standard, which governs the design and installation of fire detection systems in Belgium, precisely distinguishes this restricted alarm level from the next level, the general alarm. This distinction allows verification before triggering a complete evacuation, particularly in case of technical false alarms. The transition from one level to the next depends on the intervention, or lack thereof, of a designated person within the timeframe provided by the system programming.

Who is the surveillance officer and what must they do as a priority?

The surveillance officer is the person designated by the operator, present on site or on call, responsible for physically going to the signalled zone to verify whether it is a real fire or a false alarm. This function is provided for by the fire prevention organisation required in workplaces, under the Code on Well-being at Work (Book III, Title 3).

This officer has a verification timeframe set during system programming, based on the building's risk and estimated propagation time. If they confirm a fire, they manually trigger the general alarm without waiting for the timeframe to expire. If they do not present themselves at the panel or do not confirm within the allotted time, the general alarm triggers automatically, without additional human intervention. This delay is never several tens of minutes: it is solely intended to avoid unnecessary evacuations for spurious activations.

How does the remote monitoring centre intervene in the alert chain?

The remote monitoring centre is a remote station connected to the detection system through a specific contract, subscribed by the operator when the building is not permanently occupied, at night or on weekends for example. It receives the restricted or general alarm signal depending on the programming chosen, and can relay the information to the emergency zone if no officer is present on site to verify.

This remote monitoring is not systematically mandatory: it depends on the type of building, its occupation and the risk analysis carried out with the prevention adviser. However, it is a useful complement wherever continuous human presence cannot be guaranteed. The connection must be consistent with the overall system design described in NBN S21-100-1, and be subject to regular maintenance in accordance with NBN S21-100-2, which sets out the control and maintenance procedures for installations.

When and how is the emergency zone alerted?

The emergency zone (hulpverleningszone) is alerted as soon as the general alarm is triggered, either directly by the officer who calls the emergency services after confirming the fire, or automatically by the remote monitoring centre according to the contract in place. There is no delay at this stage: the call must be made without waiting.

Emergency zones also intervene upstream, when providing opinions on building files and during periodic inspections of installations, in addition to the technical checks provided for by NBN S21-100-2. They are therefore both recipients of the alert in real time and actors in checking the installation's compliance before any incident. The number and call procedure must be clearly stated in the posted instructions and in the building's safety register.

When are occupants informed and how does evacuation proceed?

Occupants are informed only when the general alarm is triggered, by siren, pre-recorded voice message or audible and visual signal depending on the installed equipment. Before this stage, as long as the alarm remains restricted, they are deliberately not alerted to avoid repeated evacuations for unconfirmed signals.

Once the general alarm is triggered, evacuation must follow the plan provided by the operator, with an identified assembly point and a headcount of those present. In buildings classified as medium or high under the Royal Decree of 7 July 1994, evacuation times and routes are dimensioned from the design stage to account for height and occupancy density. Experience shows that the speed of this phase depends mainly on the clarity of posted instructions and the frequency of evacuation drills organised with the prevention adviser.

What timeframes concretely separate the restricted alarm from the general alarm?

The timeframe between these two levels is not set by a single universal figure in Belgian regulations: it is determined case by case during system design, according to the building's risk and its human surveillance. The table below summarises the two levels and what they entail.

This two-stage operation reconciles two contradictory requirements: avoiding unnecessary evacuations linked to spurious activations, and ensuring that a real fire triggers the general alarm without excessive delay if no one confirms in time.