The long-awaited BS 9991:2024 – Fire safety in the design, management and use of residential buildings, represents one of the most significant overhauls to residential fire safety in nearly a decade. With the introduction of buildings over 18m requiring two stair cores, and that all buildings with passenger lifts regardless of height require evacuation lifts, has substantially changed layouts of residential buildings and therefore its smoke ventilation requirements. There are also big shifts concerning smoke ventilation systems in their purpose, design limits, and performance expectations, have all been redefined.
Below we explore the main highlights you need to know.
Focus Shift
BS 9991:2024 now provides guidance for managing people who need assistance to evacuate, which is why evacuation lifts are included in modern designs. While lifts in buildings under 18m can open directly into a stair core, those in taller buildings must open into a firefighting lobby. In practice, most designers favour a lobby arrangement even in shorter buildings, as it offers both regulatory compliance and practical usability. This shifts the smoke ventilation focus from protecting the staircase to keeping the lift lobby smoke-free, ensuring it is safe for evacuees waiting for the lift. As written within the standard, smoke systems should not extract directly from the lift lobby, as this could draw smoke in. Instead, a natural air inlet (via a shaft or Automatically Opening Vent (AOV)) combined with a Mechanical Smoke Ventilation System (MSVS) in the corridor is a standard solution. See the example arrangement below for a typical setup.

Redefinition of Height Thresholds
The 2024 edition introduces clearer height-based thresholds for the type of system:
- AOVs: no longer recommended above 18m (previously 30m).
- Natural smoke shafts: limited to 30m maximum building height (previously no limit).
- Mechanical Smoke Ventilation System (MSVS) or Pressure Differential Systems (PDS), suitable for all building heights but must be used for any >30m.
These stricter thresholds aim to ensure predictable smoke behaviour and system performance at height.
Mechanical Smoke Ventilation Systems (MSVS) Under the Microscope
Where an MSVS is used:
- The design is typically verified using computational fluid dynamics (CFD) modelling. Instead of relying on comparative assessments against a code-compliant solution (e.g., a natural smoke shaft), performance must now be proven deterministically by demonstrating that the system meets defined criteria, such as protecting the stair core or evacuation lobby during escape and firefighting.
- Integration with HVAC systems is allowed only if the entire network meets smoke-control criteria (e.g. smoke control dampers and multi-compartment smoke control duct etc.).
- As clarified in Corrigendum 01 (June 2025), section 20.2.2.3, for buildings over 60m in height, MSVS design must also consider seasonal climatic effects on the building, in accordance with BS EN 12101-13.
- Where extended travel distances within a common corridor are permitted using sprinklers and smoke ventilation, the smoke-control system should be provided in addition to the standard stairway and/or lobby protection ventilation and designed to complement it. The corridor system should include both an extract and a fresh-air supply, ensuring that smoke is drawn away from the stair and the corridor is cleared effectively by using a two-shaft smoke-control system. Single, extract-only shaft systems are not considered reliable for maintaining tenable conditions along the extended corridor.
Construction and Component Standards
BS 9991:2024 strengthens requirements for the components and installation of smoke ventilation systems, ensuring that performance is backed by proper certification and testing rather than improvised solutions.
- All AOVs must comply with BS EN 12101-2, achieving the required aerodynamic free area (not geometric free area).
- Non-certified or retrofitted actuators on vents are no longer acceptable.
- Smoke control dampers must comply with BS EN 12101-8 and:
- Provide fire resistance (integrity) equivalent to the compartment in which they are installed.
- Be tested in accordance with BS EN 1366-10 from both sides.
- Be tested in their installed orientation (horizontal or vertical) and construction type (duct or wall).
- Achieve the leakage level S1000 (-1000Pa ambient and -300Pa under fire conditions).
- Have a minimum operations classification of C10000.
- Products tested as “smoke rated fire doors” are not acceptable replacements for smoke control dampers even if they have additional testing to BS EN 12101-2.
- The use of magnetic or electromagnetic devices to hold AOVs or dampers closed is not permitted, as these have been shown to fail under fire conditions.
- Smoke shafts must be of Class A1 materials, fully sealed with a smooth internal finish, and achieve a leakage rate ≤ 3.8m³/hr/m² at 50Pa under negative pressure.
Maintenance, Testing, and Ongoing Compliance
The revised standard reinforces ongoing responsibilities under the Fire Safety Regulations 2022 and Regulatory Reform (Fire Safety) Order 2005 and Building Safety Act 2022:
- Like BS 9991:2024, there is now included Annex I: Routine inspection and maintenance of fire safety installations. Greater clarity on specific smoke ventilation requirements is available in the free Smoke Control Association (SCA) Guidance on Maintenance of Smoke Control Equipment.
For residential buildings that are <18m:
- The Fire Safety Order 2005 mandates that life-safety systems, such as smoke ventilation systems, must be maintained and tested “as often as necessary” to prevent risks of death or serious injury in the event of a fire. BS 9991:2024 builds on the previous revision regarding information for fire and rescues service by specifically including smoke ventilation. It states where not otherwise accounted for (see following bullet point) residential buildings with a top storey more than 11m about ground should be provided with a secure information box, which should include relevant information (operating instruction & access codes) for smoke ventilation systems. Along with simple floor plans indicating firefighting facilities e.g. smoke ventilation.
For residential high-rise buildings (>18m):
- Under The Fire Safety (England) Regulations 2022, it makes it a legal requirement that:
- Monthly testing of smoke ventilation systems is conducted and records kept, accessible to residents of the building. This should also include testing the interface between the fire detection/alarm system and the smoke ventilation system to ensure it operates correctly.
- For firefighting equipment including smoke ventilation, notify local fire and rescue services electronically of any faults that cannot be rectified within 24 hours, and again once fixed.
- Consider the impact of the fault on means of escape and the need for mitigation measures.
- Consider placing signs on/by defective equipment regardless of repair time.
- Update the building’s fire risk assessment if necessary to ensure compliance under the Fire Safety Order 2005.
- Ensure certain information is readily available for fire and rescue services via a secure information box, including floor plans and central controls for smoke ventilation systems.
- Under the Building Safety Act 2022, this information must form part of the “Golden Thread” for high-risk buildings: digital, secure, accurate, up to date, and accessible.
Other Changes with BS 9991:2024 Effecting Smoke Ventilation Systems
- For small single stairs
- Electrical services should be enclosed within a riser that is separated from the rest of the stair enclosure by 30mins fire-resisting construction. The service riser should not contain any equipment. Access to the service riser should be by an E 30 Sa4 or FD 30S fire door and kept locked.
- The travel distance within the lobby cannot be increased with the provision of sprinkler protection.
- As per Table 3, if the lowest floor is >10 below ground level, then must use a Pressure Differential System (PDS) in accordance with
BS EN 12101-13. - Table 1 – Protected lobby and protected corridor ventilation
- Clarification on smoke ventilation of car parks lobbies. Often under 2015 this was specified as 0.4m² permanent ventilation following section 14.1.6, although table 13 did require 1.0m² geometric free area AOV. Now for car parks either 1.0m² permanent ventilation or via an AOV achieving 0.7m² aerodynamic free area.
- Lobby ventilation to accommodation areas such as communal lounges, storage areas etc still either 1.0m² geometric free area permanent ventilation or 0.4m² geometric free area permanent ventilation with sprinklers throughout the basement, however now can be in accordance with BS 9251:2021 not just BS EN 12845.
- The newly added Figures 27 & 28 – Clarification of recommendations for lobby ventilation – Table 1 add to understand Table 1.
- Refuse lobbies should be provided with 0.2m² permanent ventilation or equivalent mechanical ventilation to prevent the build-up fumes odours as per
BS 5906:2005.Therefore, not for smoke ventilation, which has an impact on controls and damper selection. - Even when there is an alternative-direction travel, sprinklers within apartments and smoke ventilation within the corridors the maximum travel is 45m not 60m allowed under
BS 9991:2015. - As clarified in Corrigendum 01 (June 2025), basement smoke shafts should discharge smoke directly into open air at or above ground level. See section 20.3.2.3 of
BS 9991:2024. - No services within the smoke shafts, including control devices for the smoke ventilation other than actuators and final cable connections.
- Figure 31 – Examples of final exit route and protection from stairways and evacuation lifts, gives clearer examples than the 2015 review by now also including the areas that required smoke ventilation.
- As per amended in Corrigendum 01, in buildings using multi-stairs, where there is a dead-end section of corridor which is provided with a smoke control system to protect the staircase, the travel distance within this section of corridor to the staircase lobby is limited to 7.5 m, even if sprinklers are provided. This cannot be increased unless the staircase is provided with a protected lobby and smoke control systems are provided to both the lobby and corridor. See section 7.2.5 and Figure 10.
- However contrary to the above bullet point, as per Figure 8 for single-stair buildings 11m – 18m if the corridor is ventilated and sprinklers provided the maximum travel distance is 15m.
- The maximum travel distance along a single-direction (dead-end) corridor at a T-junction can now be increased from 7.5m to 15m, provided the corridor is smoke-ventilated and the building is sprinkler-protected. The total travel distance from the furthest dwelling to the nearest stair will depend on the layout: in typical two-stair arrangement, this can be up to 30m, or up to 45m if there is a protected, ventilated lobby in front of the stair core.
Summary: What This Means for Designers and Developers
- Expect more smoke shafts and AOVs per core due to evacuation lift lobby protection and extended travel corridor requirements.
- Natural systems restricted to lower buildings; MSVS & PDS required for >30m.
- CFD validation and interdisciplinary coordination required for high-risk buildings (HRB) requiring Gateway 2 approval.
- Component certification and secondary power resilience under greater scrutiny.
- Examples of common escape routes and operation of AOVs per detection or manual call points included.
This document provides a summary of the key smoke ventilation changes in BS 9991:2024 from the previous 2015 version. However, this is not an exhaustive list.
How Teal Products Can Help You Meet BS 9991:2024
Through our extensive range of industry-leading mechanical and natural smoke control solutions, combined with years of expertise, we provide solutions tailored to your building that are fully compliant with the requirements of BS 9991:2024.
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