What makes fire detection particular on a Seveso site?
A Seveso site stores hazardous substances beyond thresholds set by the Seveso III Directive, transposed into Belgian law by a cooperation agreement between the Federal State and the Regions. Fire detection must cover three simultaneous phenomena: conventional fire outbreak, explosive atmosphere linked to flammable vapours or dusts, and sometimes toxic leakage preceding any fire. A system designed for an ordinary tertiary building does not meet these constraints: conventional optical smoke detectors are unsuitable in a zone where solvent vapours can distort detection or, worse, ignite on contact with a non-certified component. The starting point is therefore never the manufacturer's catalogue, but the site's risk analysis, cross-referenced with the conditions imposed by the environmental permit and the design requirements of standard NBN S 21-100-1.
How does the environmental permit frame detection equipment?
The environmental permit is the regional authorisation (issued in Wallonia, Flanders or Brussels depending on the establishment's location) that sets the operating conditions for a classified installation. For a site storing hazardous products, these particular conditions may require a detection system connected to an alarm, a smoke extraction device or specific gas detection depending on the nature of the substances present. The permit generally refers to the site's risk analysis to specify the expected technical requirement level, but it never replaces installation standards: design remains governed by NBN S 21-100-1, maintenance by NBN S 21-100-2. The prevention adviser must verify that the technical choices made meet the conditions written in the permit document, as this is the document that the emergency zone (hulpverleningszone) will consult first during an inspection.
What role does ATEX risk analysis play in detector choice?
The ATEX risk analysis (explosive atmospheres) divides the site into explosion risk zones: zones 0, 1, 2 for gases and vapours, zones 20, 21, 22 for combustible dusts. This classification is not an administrative formality: it directly conditions the equipment authorised inside each zone. Any detector installed in an ATEX zone must bear its own marking (equipment category, gas group, temperature class) consistent with the zone where it is placed. A detector not certified for the identified atmosphere itself becomes a potential ignition source. ATEX analysis also guides the choice between gas detection (anticipating leakage before any ignition) and flame or smoke detection (reacting to combustion already started). Without this documented analysis, no serious design office can size the detection system for a Seveso site.
Which types of detectors are suitable for a site storing hazardous products?
Detector choice depends on the type of risk identified (flammable gas leak, rapid liquid combustion, smouldering fire in solid storage) and the environment (dust, vapours, high storage height). No single detector covers all situations on an industrial risk site.
| Detector type | Principle | Typical use | Main limitation |
|---|---|---|---|
| Gas detector (catalytic, infrared, electrochemical) | Measures the concentration of a gas or vapour in the air | Flammable or toxic product leak before any fire outbreak | Specific to a target gas, requires regular calibration |
| Flame detector (UV, IR or UV/IR) | Detects radiation emitted by combustion | Flammable liquid storage, outdoor areas, tanks | Requires direct line of sight to potential fire source |
| Multi-criteria detector (smoke, heat, CO) | Combines several signals to reduce false alarms | Dusty or humid industrial environments | Higher cost and configuration complexity |
| Linear smoke detector (optical beam) | Covers an axis between transmitter and receiver | High-ceiling warehouses, storage halls | Sensitive to ambient dust and vapours |
How to define zoning and alarm time delay on these sites?
Zoning consists of dividing the site into distinct detection zones (storage zone, ATEX zone, technical rooms, offices), each capable of triggering a localised alarm before the general alarm. This division, required by NBN S 21-100-1, allows immediate identification of the zone concerned and adaptation of the response (confinement, installation shutdown, partial or total evacuation). Time delay is the programmed delay between detection of an incident start and triggering of the general alarm: it allows time for a trained team to verify the reality of the alert before evacuating a site where a production shutdown can itself generate a risk. On a Seveso site, this delay must remain compatible with the kinetics of the danger identified in the risk analysis: a toxic gas leak does not tolerate the same time delay as a smouldering fire in a pallet stock. The zoning and time delay adopted must appear in the file submitted to the emergency zone.
Who controls and maintains detection installations on a Seveso site?
Periodic maintenance of fire detection installations falls under standard NBN S 21-100-2, which sets the maintenance and control operations to be carried out on the system. Gas detectors additionally require regular calibration, the frequency of which is defined by the manufacturer and the site's risk analysis, as their drift over time can render an alarm silent in the event of a real leak. The certification bodies recognised in Belgium to certify equipment and installer compliance are BOSEC and ANPI. The territorially competent emergency zone remains the contact that gives its opinion on the file and can carry out on-site inspections, particularly for high-risk classified establishments such as Seveso sites. The site's prevention adviser should keep a dated register of all inspections and calibrations, a document regularly requested during inspections.