What does a change of use imply for fire detection?
A change of use refers to any modification of the purpose of a room or building that changes the nature or quantity of combustible loads, human occupancy, or ignition sources present. Moving from offices to workshop or warehouse directly modifies the parameters on which the initial detection installation was designed: the fire load, the presence of dust or vapours, the number and mobility of occupants. Fire detection installation is never fixed in time: it was dimensioned according to standard NBN S 21-100-1 for a specific building configuration. As soon as this configuration changes, the initial dimensioning is no longer guaranteed valid. This is why Belgian regulations, via the Royal Decree of 7 July 1994, reason in terms of building destination and classification (low-rise, medium-rise, high-rise building): a change of use can shift the applicable requirements.
Why must the fire risk analysis be redone?
The risk analysis must be repeated as soon as a change of use modifies the hazards present in the building, because the installed detection responded to a risk that no longer exists in the same way. A production workshop generates dust, solvent vapours or heat sources that offices do not produce. A storage warehouse increases the fire load per square metre and modifies the possible fire spread. The Code on Well-being at Work (Book III, Title 3) requires the employer to assess fire risks in the workplace and to reassess them when conditions change. The company's prevention advisor, in conjunction with the BOSEC certified installer, must therefore repeat this analysis before any technical decision on detection: type of detectors, zoning, number of detection points, and not the other way around.
How to revise the technical documentation of the installation after a change of use?
The technical documentation of the fire detection installation must be updated to reflect the new building configuration, in accordance with standard NBN S 21-100-2 relating to maintenance and control. This revision covers several elements: the detection zoning plan, the choice of technologies (optical smoke detectors, heat detectors, linear detection), the location of signalling devices, and alarm procedures in case of evacuation. A workshop with machine tools or a warehouse with high-level storage often requires different technologies from those suited to offices. Revising the documentation is not an administrative formality: it determines the reliability of detection. An optical smoke detector installed for offices can, for example, generate false alarms in a dusty environment, or conversely miss a fire start masked by the activities of the new use.
Is a new acceptance of the detection installation required?
A new acceptance of the installation is necessary when the change of use results in a substantial modification of the existing detection installation, and not a simple minor adaptation. If the zoning, number of detectors or detection control panel are significantly modified, the modified installation must undergo a pre-commissioning inspection, in the same way as a new installation according to the principles of NBN S 21-100-1. The territorially competent emergency zone (hulpverleningszone) may be consulted for advice, particularly if the change of use modifies the building classification within the meaning of the Royal Decree of 7 July 1994. In all cases, the operator has an interest in documenting this new acceptance: it serves as a reference for subsequent periodic inspections and protects the company in case of loss, particularly with regard to insurance.
Concrete case: from an office floor to a carpentry workshop
A tertiary building equipped with optical smoke detector detection, dimensioned for offices, was converted into a carpentry workshop by its owner. The activity immediately generated wood dust in suspension, causing repeated false alarms of the detection control panel. The risk analysis repeated with the prevention advisor highlighted two problems: optical detectors unsuited to the dusty environment, and a fire load significantly higher than originally planned due to the storage of panels and solvents. The solution consisted of replacing part of the optical detection with multi-criteria detectors and heat detection in the cutting areas, then reviewing the zoning to isolate the solvent storage area. The technical documentation was completely revised and a new acceptance was organised with the installer before full recommissioning of the control panel.
What mistakes should be avoided during a change of use?
The most common mistake is to keep the existing detection installation without verification, considering that it remains valid because it still works technically. An installation can be operational in the electrical sense while being totally unsuited to the new fire risk of the building. Another mistake is to modify the activity gradually, without ever formalising the change of use with the prevention advisor or the emergency zone, which delays compliance until a periodic inspection or a loss. Finally, some operators neglect to update the technical documentation of the installation even though the equipment has been modified in the field: this gap between the documentation and the installed reality greatly complicates maintenance interventions and inspections according to NBN S 21-100-2.
Comparison: offices, workshop, warehouse, what differences for detection?
| Criterion | Offices | Production workshop | Storage warehouse |
|---|---|---|---|
| Fire load | Low to moderate | Moderate to high depending on process | Often high depending on goods |
| Environment | Clean, little dust | Dust, possible vapours | Variable, significant storage height |
| Suitable technology | Optical smoke detectors | Multi-criteria detectors, heat detectors | Linear detection, aspiration depending on height |
| Human occupancy | Continuous, dense | Continuous, fixed workstations | Occasional, low density |