Rzeczoznawca, ochrona przeciwpożarowa

A significant problem frequently encountered by fire detection and fire alarm system designers is the protection of building voids, including the spaces above suspended ceilings and under raised floors. In the specification PKN-CEN/TS 54-14:2006, which was valid until recently, building voids fulfilling the following conditions were exempt from protection by automatic detectors:* there is no possibility of significant fire or smoke spreading through the building void beyond the room of fire origin before it is detected by detectors located outside the void, or* a fire in the building void cannot damage safety system cables before the fire is detected.

The specification specified that a building void does not require separate protection when:* it has a height of less than 1 m, and* it has a length of less than 10 m, and* it has a width of less than 10 m, and* it is completely enclosed by elements made of non-combustible material, and* the combustible material is distributed in such a way that the fire load density does not exceed 25 MJ per 1 m² of area, and* safety system cables are not routed through it (unless the cable has a fire resistance of at least 30 min).

The amendment to the specification in question, PKN-CEN/TS 54-14:2020-09, recently published by PKN, introduces significant changes in this scope, unfortunately also introducing serious inconsistencies in the guidelines. In the current version of the specification, the size parameters of the building void (height, width, and height) have been abandoned, and there is no reference to the combustibility of the enclosure of this space. Currently, the single factor is the fire load in this space. However, regarding the fire load, the specification refers only to its Annex C, i.e., the fire load caused by cables in this space, which, from the perspective of the possibility of fire spread, is not the only factor affecting fire development.

Currently, in clause 5.3.9 of the specification, it is indicated that voids do not require protection by automatic detectors if:* there is no possibility of significant fire or smoke spreading through the building void beyond the room of fire origin before it is detected by detectors located outside the void, or* a fire in the building void cannot damage safety system cables before the fire is detected.

And that is where the similarity with the previous wording of the specification ends. Further on, there are provisions stating that voids do not require protection by independent detectors if they:* do not contain a fire load exceeding 25 MJ on any 1 m² of area; and* do not contain a fire load greater than 15 MJ on any 1 m² if the void contains safety system cables.

Up to this point, everything is clear. The problem begins when we read the provisions of clause 6.5.1 g), which refer to the arrangement of detectors above a suspended ceiling as well as in other similar horizontal voids. This clause makes the protection of these spaces dependent on the fire load, but note: taking into account the ceiling construction and the presence of fire detection and fire alarm system cables in this void. One might ask: what about a combustible floor slab construction, which nevertheless occurs in existing buildings? A further contradiction lies in the fact that previously we had a general requirement regarding the fire load per square meter of void area—thus a local value rather than an averaged one across the entire void—whereas here we have a provision stating that in spaces exceeding 200 m², the fire load value cannot be averaged and the load for cable routes must be calculated separately for each square meter of area, implying that for smaller areas averaging would be permissible; moreover, we again have a reference only to the load originating from cable routes while ignoring the building structure. The remaining requirements no longer raise doubts; they make the protection of the space dependent on the presence of fire alarm cables and possibly their location relative to power installations. Rather than ending these solutions merely by pointing out doubts, below is my proposal for designers in individual cases:* suspended ceiling or raised floor made of combustible materials with a classification lower than non-ignitable, or floor slab construction made of combustible materials with a classification lower than non-ignitable — we always use protection by automatic detectors regardless of the load caused by cables or the presence of safety system cables;* suspended ceiling or raised floor made of non-combustible or non-ignitable materials, and floor slab construction made of non-combustible or non-ignitable materials, with a fire load exceeding 25 MJ per any square meter of void area caused by combustible installations in the void — we use detectors arranged according to coverage radii, provided that no detector is located further than 5 m from cable routes running through these spaces;* suspended ceiling or raised floor made of non-combustible or non-ignitable materials, and floor slab construction made of non-combustible or non-ignitable materials, with a fire load not exceeding 25 MJ on any square meter of void area and exceeding 15 MJ on any square meter of void area caused by combustible installations in the void — we use detectors if safety system cables run through the space that do not have a fire resistance of at least PH 30 and are not constructed using cable assemblies ensuring signal and power delivery for the required operating time of the fire protection equipment, but not less than 30 minutes;* suspended ceiling or raised floor made of non-combustible or non-ignitable materials, and floor slab construction made of non-combustible or non-ignitable materials, with a fire load not exceeding 15 MJ on any square meter of void area caused by combustible installations in the void — does not require detectors if the safety system cables have a fire resistance of at least PH 30 and are constructed using cable assemblies ensuring signal and power delivery for the required operating time of the fire protection equipment, but not less than 30 minutes, or are located at least 0.5 m away from power installations.

The terms "non-combustible" and "non-ignitable" mentioned above should be defined in accordance with the regulation on technical conditions to be met by buildings and their location, i.e., materials with a reaction to fire class of at least A1, A2, or B. However, regarding the fire load calculation, keeping real hazards in mind, we should take into account all combustible installations running through the given space and not just the insulation of cables and wires, whereas structural elements of the building are not included. The lack of consistency among the above-mentioned provisions was discussed in Technical Committee No. 264 of the Polish Committee for Standardization and was submitted to the relevant CEN body to be corrected in the next version of the specification. However, until then, one must stick to rules that are technically justified.

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