What is an evacuation voice alarm system (EVAC)?
An evacuation voice alarm system, often referred to as EVAC (hulpverleningszone), broadcasts pre-recorded or live voice messages to guide occupants during a fire alert, instead of a simple audible signal. It differs from the conventional siren by its ability to transmit differentiated instructions according to the building zone: evacuate immediately in one compartment, wait in another. The EVAC is connected to the fire detection system and can be controlled manually from the control panel or by the attending fire service. This zone-based operation justifies its use in buildings where simultaneous evacuation of all levels would pose a practical problem, for example congestion of stairwells in a high-rise building.
Is fire detection sufficient without a voice alarm system?
No, detection alone is never sufficient: a fire detection installation compliant with NBN S21-100-1 must always be associated with a means of alerting occupants, but this means is not necessarily vocal. For a large number of buildings, a simple audible signal (siren, electronic horn) meeting the audibility requirements of the standard fulfils this function. The question is therefore not "detection with or without alarm", but "what type of alarm is suited to the building configuration and its occupancy". It is the risk analysis, carried out before the installation design, that determines whether a simple siren is sufficient or whether differentiated voice instructions are necessary to organise a safe evacuation.
In which buildings must evacuation be organised in phases?
The Royal Decree of 7 July 1994 establishing basic fire safety standards classifies buildings as low-rise, medium-rise and high-rise according to their height. This classification determines the permitted evacuation strategy. In a high-rise building, simultaneous evacuation of all occupants via the same stairwells is generally not the chosen solution: the building is designed to allow progressive evacuation, managed level by level or compartment by compartment. This phased management requires the ability to communicate different instructions according to the zone concerned, which only a voice alarm system can do clearly. In a low-rise building with simple occupancy (ground-floor offices, small shop), immediate general evacuation remains the rule and a siren meets this need.
What does NBN S21-100-1 say about choosing between siren and voice alarm?
The standard NBN S21-100-1, which governs the design and installation of fire detection systems in Belgium, does not set a single threshold automatically triggering the requirement for an EVAC. It requires that the choice of alarm mode result from an analysis taking into account the building's purpose, the number of occupants, their ability to evacuate independently (night-time occupancy, persons with reduced mobility) and the complexity of the evacuation route. In practical terms, this analysis points towards a voice alarm system in establishments where occupants sleep on site, where the capacity is significant, or where the building requires staged evacuation. The certified design office or installer then translates this result into the technical specifications of the installation.
In which cases does a simple siren remain sufficient?
A simple audible alarm remains compliant and sufficient when evacuation can be generalised without phasing and occupants are able to react independently to a non-verbal signal. This is the typical case of a low-rise building as defined by the Royal Decree of 7 July 1994, with daytime occupancy, short evacuation routes and few levels. A ground-floor production workshop, small office or limited-area shop generally fall into this category. However, the siren must meet the audibility requirements of NBN S21-100-1 in all relevant premises, including noisy areas or toilets, which sometimes requires several sound diffusion points even without switching to voice alarm.
Who decides whether my building needs an EVAC?
The decision results from a risk analysis conducted with the operator's prevention adviser and technically translated by the BOSEC-certified design office or installer. The territorially competent emergency zone (hulpverleningszone), consulted on the building's safety file, may also impose additional requirements related to the specific site configuration. ANPI publishes reference documents that support the practical application of NBN S21-100-1 and can usefully guide this choice. In case of doubt, it is better to settle the question before the project: integrating a voice alarm system from the design stage costs significantly less effort than adding it afterwards to an existing installation.
Siren or EVAC: quick comparison
| Criterion | Simple audible alarm (siren) | Evacuation voice alarm system (EVAC) |
|---|---|---|
| Signal type | Continuous or modulated sound, non-verbal | Pre-recorded voice message, differentiated instructions |
| Zone management | Single general alarm | Distinct instructions per compartment or level |
| Typical buildings | Low-rise buildings, simple daytime occupancy | High-rise buildings, night-time occupancy, high capacity |
| Decision basis | Simple risk analysis, short routes | NBN S21-100-1 risk analysis, phased evacuation required |
| Regulatory reference | Royal Decree of 7 July 1994, NBN S21-100-1 | Royal Decree of 7 July 1994, NBN S21-100-1, safety file validated by emergency zone |