What is a critical link in a fire detection system?
A critical link is a section of cabling whose failure during a fire would compromise detection, alarm or evacuation. This typically concerns the loop between the detection control panel and the detectors, the emergency power supply to the panel, links to sirens and sounders, as well as control links to smoke extraction or fire door release systems.
Not all links in an installation are equally critical: an information line to a monitoring station does not have the same requirements as a general alarm line. It is the responsibility of the installation designer, based on the functional analysis of the building, to determine which links must remain operational in the event of fire and for how long. NBN S 21-100-1, which governs the design and installation of fire detection systems in Belgium, requires this choice to be documented in the design file, not left to the installer's discretion on site.
What fire resistance requirements apply to fire alarm system cabling?
The general principle is that cabling for critical links must maintain its functional integrity for a duration compatible with the building's evacuation scenario, even when exposed to flames. This duration depends on the building category defined by the Royal Decree of 7 July 1994 (low-rise, medium-rise or high-rise building) and the evacuation strategy adopted.
In practice, this translates into selecting cables tested to maintain electrical continuity under fire exposure, according to standardized European tests (test standard EN 50200 is the most common reference for this type of cable, with endurance classes expressed in minutes). The designer sets the required duration for each link identified as critical, and this requirement must appear in the file submitted before acceptance. An ordinary cable, even of good electrical quality, does not meet this requirement if it has not been tested and certified for fire resistance.
What do the RF1h and RO designations on fire cables mean?
In common technical terminology, RF1h designates a cable whose electrical continuity is guaranteed for one hour of fire exposure, and RO designates a cable resistant to short-circuit and without flame propagation, but without extended function maintenance requirement. These commercial designations refer to test classes defined by European fire resistance standards for cables.
It is not the commercial designation that is authoritative, but the manufacturer's test certificate and its consistency with the requirement set in the installation design file. In the same building, several types of cables are typically found depending on the link function: a high fire resistance cable on general alarm and smoke extraction control links, a non-flame-propagating cable on less critical links. The prevention advisor or design office must be able to justify this choice link by link, not globally for the entire installation.
How should fire-rated penetrations of fire alarm cabling be treated?
A fire-rated penetration is the point where a cable passes through a wall or slab separating two compartments. This passage must be sealed with a certified material to restore the fire resistance rating of the original wall, otherwise the cabling itself becomes a path for fire and smoke propagation between compartments.
The Royal Decree of 7 July 1994 imposes compartmentation requirements according to building height (low-rise, medium-rise, high-rise), and poorly executed firestopping negates the effect of compartmentation even if walls and floors are correctly dimensioned. On site, each penetration must be identified, sealed with a product suitable for the wall type (concrete, plasterboard, lightweight partition) and documented by a technical sheet or dated photograph. This is a point that emergency zones (hulpverleningszones) systematically check during their visits, as it is one of the most frequently found defects in new installations.
What points should be checked when accepting a fire detection installation?
Acceptance of a fire detection installation must include a specific check of critical link cabling, separate from the simple functional test of detectors. This involves verifying that the installed cable corresponds to the type prescribed in the design file, not just that the alarm triggers correctly in testing.
Concrete points to verify:
- 1.Certificates for cables used on links identified as critical correspond to the fire resistance requirements set in the design file.
- 2.Each fire-rated penetration is sealed and documented, with visible identification on site.
- 3.Cable routes do not run alongside particularly high-risk areas (technical rooms with high fire load) without additional protection.
- 4.Consistency between the submitted cabling plan and the actually installed cabling is verified point by point, not by sampling.
These verifications determine the validity of the file submitted to the emergency zone and serve as the basis for the maintenance plan required by NBN S 21-100-2.
Who checks cabling compliance during periodic inspections?
Periodic inspection of a fire detection installation, carried out according to NBN S 21-100-2, includes a visual examination of the condition of cabling and fire-rated penetrations, in addition to functional tests of detectors and the control panel. A BOSEC-certified installer, or ANPI in the context of a more thorough inspection, is authorized to carry out this type of verification.
The emergency zone retains its role of advice and control over the entire installation, including compartmentation aspects related to cable routing. In practice, degradation of penetration firestopping (subsequent drilling for a new cable, renovation work) is one of the most frequently identified defects between two periodic inspections, as it often occurs after initial acceptance, during technical interventions with no apparent connection to fire safety.