Office fire safety: bringing buildings up to code and turnkey works
Passage units: sizing exits according to the Labour Code
A category A fire safety system on a 300 sq m floor under a short lease means 15,000 EUR in extra cost for zero regulatory gain: R4227-5 and NF S 61-931 allow a category E fire safety system with a type 4 alarm. Office fire safety rests on four pillars: 1 h fire-resistant compartmentalisation (EI 60), smoke extraction for circulation areas longer than 30 m, fire safety systems from category A to E, and exits sized in passage units. Since 2006, Kytom has supported code compliance on occupied sites, with an average lead time of 12 weeks, validation by an approved inspection body and phasing by zones of 150 sq m to 250 sq m. As an Office Manager, Property Director or CFO, you often inherit the file without having chosen its timeline: a commission visit, an observation from a technical inspector, a lease signing or a refurbishment all trigger the urgency.
Exits govern evacuation and rely on the concept of the passage unit (UP): one UP equals 0.60 m, a single UP is raised to 0.90 m, and two UP correspond to 2 x 0.70 m = 1.40 m under article R 235-4-2. One UP corresponds to 0.60 m to 0.90 m in width, two UP require 1.20 m to 1.40 m, three UP require a minimum of 1.80 m.
The number of UP required depends on the theoretical occupancy of the floor:
- up to 19 people: 1 UP, 1 exit
- from 20 to 50 people: 2 UP, 2 separate exits
- from 51 to 100 people: 2 UP, 2 exits
- above 100 people: 1 additional UP per 100
Articles R4227-4 to R4227-9 require at least two opposing exits from 50 people or 300 sq m. A 0.90 m door counts as 1 UP, a 1.40 m door as 2 UP. A single staircase 1.40 m to 1.50 m wide allows a maximum occupancy of 100 people per floor under article R4227-5.
For the CFO: theoretical occupancy drives CAPEX, not actual occupancy. The administration uses the theoretical occupancy calculated on the usable area (1 person per 10 sq m in a standard office), not the number of active badges. On an 800 sq m floor occupied by 50 actual people but theoretically sized for 80, you need two 2-UP exits, that is two 1.40 m doors and two compliant stairwells. Anticipating this calculation as soon as the lease is signed avoids costly structural rework, often ranging from several tens of thousands of euros depending on the floor configuration.
Kytom checks these ratios from the preliminary design stage, before partition plans are finalised. An approved inspection body validates compliance before handover.
Contrarian view: the industry’s conventional wisdom over-applies UP to small floors. On a floor of fewer than 19 people with a single already-compliant exit and no planned change in occupancy, triggering a full UP study is disproportionate: a visual audit by a technical inspector is enough. For a fixed lease of less than 24 months, resizing exits for a theoretical occupancy never reached in practice generates a cost with no realistic payback: it is preferable to file a reasoned waiver request with the safety commission, accepted in 60% to 70% of cases according to our experience.
1 h fire-resistant compartmentalisation, high-risk rooms and smoke extraction: the 3 lines of defence
Compartmentalisation limits the spread of fire and smoke. In the office sector, three levels of protection structure the design:
- Floor perimeter: EI 60 fire doors (1 h fire-resistant) on access points to floors larger than 500 sq m, with automatic closure triggering coordinated with the fire safety system under technical instruction IT 247.
- Internal subdivision: every 25 to 30 m in circulation, and a smoke extraction zone for any volume larger than 1,000 sq m or 60 m in length.
- High-risk rooms: EI 60 isolation for archives, cleaning rooms, waste; EI 120 for server rooms and boiler rooms; EI 120 for stairwells.
Smoke extraction of horizontal circulation areas becomes mandatory from 30 m in length, with extractors slaved to the fire safety system. Summary table of fire-resistance classes:
| Element | Classification | Reference |
|---|---|---|
| Floor door >500 sq m | EI 60 | IT 247 |
| Stairwell | EI 120 | Labour Code R4227 |
| Server room | EI 120 | DTU |
| Circulation partition | EI 30 | R4227-5 |
Kytom coordinates the joiner, the fire safety system electrician and the heating engineer to ensure the slaving systems are consistent at handover. On our recent code compliance projects, the lack of coordination between joiner, fire safety system electrician and heating engineer is the main source of reservations at the safety commission.
Contrarian view: enhanced compartmentalisation is not always the right answer. Contrary to common practice, on a floor smaller than 500 sq m with no high-risk room and with direct exits to the outside, adding EI 60 doors at access points is not required by IT 247: doing so generates an extra equipment cost per door with no regulatory benefit. Doubling up mechanical smoke extraction on a length shorter than 30 m adds nothing: natural smoke extraction through facade openings remains the economical solution.
Fire safety systems category A to E: choosing the right configuration based on use and lease term
The fire safety system (SSI) combines detection, safety activation (compartmentalisation, smoke extraction, shutdown of technical installations) and the alarm. The regulations define five categories:
- SSI A: generalised automatic detection, automatic safety activation, mandatory in ERP types J, U and complex office floors.
- SSI B: partial detection, automatic safety activation of the compartments concerned.
- SSI C, D, E: simplified configurations for lower-risk buildings.
The regulatory checks of the CNPP reference frameworks apply annually: Q18 for electrical installations and the fire safety system, Q19 for automatic extinguishing systems. The signalling panel centralises alarms and faults, with relay to a room accessible 24/7.
For the Asset Manager: the fire safety system is a depreciable asset, not an expense. A well-sized category A fire safety system depreciates over 10 to 15 years and enhances the asset’s value on resale: a compliant safety commission avoids the 5% to 10% discount observed on non-compliant floors during due diligence. For an 850 sq m office floor, we generally size a category A fire safety system with 1 detector every 80 sq m, manual call points every 30 m of circulation, and a type 1 or 2a general alarm. The installed cost generally ranges from 35 EUR/sq m to 65 EUR/sq m depending on the complexity of the floor and the condition of the existing wiring. Commissioning includes a handover report, clearing of reservations and training of the Office Manager teams.
Contrarian view: the category A fire safety system is over-prescribed in offices. Below 300 sq m on a single-tenant floor with no server room or archives, a category A fire safety system can represent a significant extra cost with no real safety gain compared with a category E fire safety system with a type 4 alarm, which remains compliant and substantially reduces the equipment cost.
Method
- Initial regulatory audit
Diagnosis of the applicable regime depending on the nature of the site (workplaces or establishment open to the public), survey of gaps against the regulatory framework, cross-reading of the lease and the co-ownership rules. Kytom produces a prioritised gap report in 5 working days. - Technical study and costing
Design of the compartmentalisation, aeraulic sizing of the smoke extraction, choice of the fire safety system category. The costing is detailed by package to let you adjust the scope according to your budget. - Filing the works authorisation
Compiling the ERP file (safety notice, fire-resistance plans, certificates) and filing at the town hall. Allow 11 weeks of review on average. Kytom manages exchanges with the preventive safety commission. - Preparing the works on an occupied site
Phasing by zones of 100 to 150 sq m, acoustic protection, work scheduling during off-peak hours if needed. Formalised internal communication to staff with notices and memos. - Execution and testing
Installation of fire-resistant partitions, installation of the fire safety system, fitting of smoke extraction, certified sealing. Smoke tests and triggering tests carried out in the presence of the approved inspection body. - Handover and operating file
Handover visit with the commission, delivery of the complete works file (notices, plans, certificates), staff training on evacuation. Kytom offers annual monitoring coordinated with the maintenance of the other technical packages.
Frequently asked questions
Which fire safety system category for a 500 sq m office floor?
Below 500 sq m with no high-risk room, a category E fire safety system with a type 4 alarm is sufficient. Above that, or with a server room/archives, a category A fire safety system becomes relevant. Systematic validation by an approved inspection body before finalising the design.
