Smoke control fire safety: smoke vents, IFG, public-access building compliance

Smoke control in offices falls under three complementary frameworks, each with its own triggering thresholds.

• Regulatory framework applicable to non-ERP commercial buildings: article R4216-30 requires the treatment of windowless or basement rooms, and articles R4216-1 to R4216-34 govern exits and evacuation.
• Type W public-access building regulations (offices receiving the public beyond 100 people): provisions DF 1 to DF 11 apply to circulation routes of more than 30 m and to enclosed staircases.
• ITGH 25 (high-rise buildings, with the lowest floor of the top level above 50 m): systematic mechanical smoke control, compartments of 750 m² maximum, dedicated fire-resistant ducts.

Technical instruction IT 246 sets the calculation rules: effective smoke vent area (SUE) at least equal to 1/100 of the floor area for natural smoke control, flow rate of 1 m³/s per m² for mechanical systems. In type W public-access buildings, we generally target a ratio of around 1 m² of smoke vent for every 250 m² of floor area, with systematic verification of the Technical Approvals of the products installed.

Our interpretation differs from common practice on one specific point. The conventional wisdom in the profession treats natural smoke control as a default option as soon as it is technically permitted. In practice, on projects under 400 m², installing motorised smoke vents generates a significant additional cost with no measurable operational gain compared with compliant facade openings. Below 300 m² of floor plate or on a ground floor with no circulation constraint, smoke control via facade openings is sufficient. Conversely, in basements and in horizontal circulation routes of more than 30 m, natural smoke control is excluded by IT 246: only mechanical smoke control is permitted.

Kytom’s four-step method, average lead time 12 weeks

The method unfolds across four successive steps, applied by the Kytom teams since 2006. The average lead time of 12 weeks between audit and handover reflects our experience on recently delivered operations.

1. Regulatory audit: cross-referencing IT 246, type W public-access building regulations and the requirements applicable to workplaces (R4216-30), identifying gaps, verifying the Technical Approvals of the equipment in place.
2. Sizing: calculation of the SUE per smoke compartment of 1600 m² maximum, choice between natural smoke control via certified smoke vents and mechanical smoke control via fans rated 400 °C/2h, free air inlets equal to 1.5 times the extraction area.
3. Design and integration: coordination with the category A SSI, connection to safety-operated devices (DAS), manual controls at fire brigade access points.
4. Commissioning: flow rate checks with an anemometer, trigger tests, handover of the SSI identity file, training of operators on the safety register.

The associated compartmentation requires 1-hour fire doors (EI 60) at access points to floor plates larger than 500 m², with automatic closures controlled in accordance with IT 247. The branches manage the structural, electrical and HVAC packages in-house, which avoids loss of information on complex projects.

For the thermal engineer: hydraulically separating HVAC and smoke control, the error that reclassifies the entire project

The subject is poorly framed as soon as it is linked to thermal comfort. For the thermal-energy engineer, the temptation is to share fans, ducts and controllers between HVAC and smoke control: an apparent investment saving, space gains in the plenum, simplification of the BMS. This pooling is the leading cause of IT 246 non-compliance observed on operations taken over second-hand: it systematically generates significant maintenance overcosts compared with an installation properly separated from the outset.

Three rules structure the design on the energy side:

• Network separation: smoke control fans rated 400 °C/2h on dedicated electrical circuits, powered downstream of the SSI, with no aeraulic link to the comfort AHU. Any pooling triggers a complete reclassification at the commission.
• Distinct aeraulic balance: the smoke control SUE cannot be offset by hygienic air renewal flow rates. The free air inlets equal to 1.5 times the extraction area are calculated independently of the RT/RE2020 air change rate.
• BMS for monitoring, not control: the supervision system can display the status of the DAS and the 400 °C fans, but control remains hard-wired to the category A SSI. This is a structural constraint, not an architectural option.

The CNPP Q19 standard adds an annual infrared thermography of the electrical panels powering the SSI, a check often overlooked in standard multi-technical maintenance plans.

Measured benefits and upstream trade-offs on occupied sites or high-rise buildings

Feedback from delivered operations shows a high rate of compliance on the first pass before the safety commission, provided the technical file and acceptance tests have been rigorously conducted upstream. Economically, a mechanical smoke control system correctly sized from the outset generates annual maintenance costs significantly lower than those of an undersized installation taken over second-hand, where iterative compliance upgrades durably weigh down the operating budget. The asset valuation of certified buildings in operation remains a parameter tracked by real estate brokers, with no consolidated public figures to date.

Three operational constraints warrant an upstream trade-off:

• Work on an occupied site: SSI shutdowns require a hot-work permit, reinforced human surveillance and a night or weekend schedule, with a significant increase in project cost.
• HVAC/smoke control separation: smoke control fans must remain separate from the comfort networks, on pain of complete reclassification and the risk of IT 246 non-compliance.
• High-rise above 50 m: ITGH 25 requires fire-resistant ducts and compartments of 750 m² maximum, which can substantially increase the mechanical extraction budget.