Innovation Fire Engineering have completed four internal CFD case studies to investigate various ventilation strategies for both the common corridor and the evacuation lift lobby within a residential building. A total of four possible ventilation options have been assessed – as shown in the table below.
The silver medal for ventilating an evacuation lift lobby goes to Solution 2, see details below.
Table 1 – Ventilation options modelled in Solutions 1–4
| Solution | Common Corridor | Evacuation Lift Lobby |
| 1 (‘Code-compliant’) | 1.5m² Natural Shaft | 1.5m² natural smoke shaft |
| 2 (‘Fire Engineered’) | Mechanical Shaft | Cross-vented via stair AOV (double ‘floppy door’) |
| 3 (‘Fire Engineered’) | Mechanical Shaft | 1.5m² natural smoke shaft |
| 4 (‘Fire Engineered’) | Mechanical Shaft | 1.5m² AOV |
Background
In March 2024, amendments were made to Approved Document B Volume 1 (ADB V1) seeking to provide new guidance on residential buildings over 18m and evacuation lift lobbies. As well as requiring a second stair in residential buildings taller than 18m, ADB V1 amendments stated that an evacuation lift lobby should provide a refuge area for those waiting for the evacuation lift, to not be directly accessible from any flat and that any smoke control system designed to protect the staircase should extend the same level of protection to the evacuation lift and evacuation lift lobby.
CFD Modelling Details – Solution 2
The CFD geometry is based on a generic corridor and lift lobby arrangement, whereby the maximum single direction travel distance within the common corridor is 7.5m (ADB Vol 1). Building height is assumed to be over 30m and the single stair modelled to its full height. The corridor is assumed to be a dead-end portion.
In Solution 2, the common corridor is ventilated via a 0.6m² mechanical smoke shaft. The evacuation lift lobby is unvented, with both the lobby and stair doors assumed to be pulled open by the smoke extract fan (‘floppy door design’). This allows resupply air via the head of stair 1m² AOV.
The fire size, CFD parameters, and timeline are consistent with industry practice and guidance.
Figure 1 – Solution 2 CFD domain (plan view)
CFD Results – Solution 2
Please see the smoke and visibility videos below.
For Solution 2, the evacuation lift lobby and stair remain free from smoke ingress, providing acceptable conditions during escape and firefighting.
Discussion
The CFD results for Solution 2 show acceptable conditions. However, door opening forces and corridor pressures would need further testing, as the design relies on two doors being pulled open by the extract fan. This may increase risk compared to a single-door design.
It would be great to hear thoughts on Solution 2.
Next week, in our final article covering Solutions 3 and 4, we will be awarding the Gold Medal in our CFD Evacuation Lift Olympics.
