Smoke Ventilation - ODPM Project FP
By Stewart Miles, Senior Consultant, BRE Fire and Security.
As part of a research programme for the Buildings Division of the Office of the Deputy Prime Minister (ODPM) to support and underpin the development of Part B of the Building Regulations for England and Wales and its supporting guidance, BRE has recently completed a project to examine the smoke ventilation of common access areas of flats and maisonettes and their relationship to the provision of Compartmentation and Means of Escape procedures.
As part of a research programme for the Buildings Division of the Office of the Deputy Prime Minister (ODPM) to support and underpin the development of Part B of the Building Regulations for England and Wales and its supporting guidance, BRE has recently completed a project to examine the smoke ventilation of common access areas of flats and maisonettes and their relationship to the provision of Compartmentation and Means of Escape procedures.
Smoke containment, provided by the provisions for compartmentation and smoke-rated fire doors, and coupled with limiting travel distances, plays a key role in the overall smoke management strategy for flats and maisonettes. Furthermore, the additional benefit to life safety provided by two escape paths, and when present two escape stairs, has been underlined by the project findings.
Where smoke does enter the common access areas, smoke ventilation and control measures can offer varying levels of additional protection. Assisted by project partners Buro Happold and the University of Ulster, and with guidance from a Steering Group, a range of such smoke ventilation measures were investigated using Computational Fluid Dynamics (CFD) and reduced-scale physical modelling. Supported also by a review of published research and current practice in the UK and overseas, the project has considered both the initial stages of a fire where occupants would be making their escape, and also later stages where fire fighting operations may have commenced or evacuation from other building stories be required.
The range of smoke ventilation schemes investigated includes external wall ventilators, naturally ventilated smoke shafts, mechanical smoke exhaust from the corridor and pressurisation of the stairway with and without smoke/air relief from the corridor. In both the physical-scale experiments and the CFD simulations the transport of smoke and heat from a dwelling fire into adjoining corridors and stairs has been examined. Provisions for replacement air and the influence of adverse wind and stack pressures was also investigated.
Figure 1 illustrates part of the 1/5th scale physical model, showing smoke travelling along the ceiling of a corridor in one of the experiments. The model also included a stair and lobby section, and allowed a range of natural and mechanical smoke ventilation schemes to be studied.
Figure 2 shows a typical output from BRE's CFD fire model JASMINE, here showing contour plots of temperature for a scenario with a naturally ventilated smoke shaft where some smoke enters the stairwell.
The project has demonstrated that, if exposed to smoke from a dwelling fire for more than a short duration, the adjoining common corridor / lobby can be expected, in general, to become smoke filled. While external wall vents to the lobby / corridor may then in some circumstances maintain tenable conditions inside these spaces, in general an engineered mechanical solution would be required to achieve this. This could be in the form of either a smoke extraction scheme or a pressurisation scheme with protection extended into the common corridors.
If the remit of the smoke ventilation scheme is primarily to offer additional smoke protection to the common stair, then a range of natural and mechanical approaches are suitable. Arguably the simplest and most robust approach is provided by external wall ventilators located in the adjoining common lobby / corridor. The project has demonstrated that a higher level of protection can be provided by a naturally ventilated smoke shaft located in the lobby / corridor. This serves to draw smoke from the corridor and depressurise the corridor relative to the adjoining stair. However, such a smoke shaft arguably requires greater design effort and post-occupation maintenance than an external wall ventilator.
Alternatively, air/smoke can be mechanically extracted from the corridor and, provided replacement air provisions are made, the stair can be protected from smoke ingress. Stair pressurisation, with air/smoke relief from the corridor, provides an alternative means of mechanically protecting the stair. These mechanical schemes can be designed according to non-fire pressure differential and open door air speed criteria, and in general will be more robust with respect to adverse wind and building stack pressures than external wall ventilators or naturally ventilated smoke shafts.
A final report, giving details of the whole project, including the modelling studies and the review, will be available to the public from the BRE website.
Where smoke does enter the common access areas, smoke ventilation and control measures can offer varying levels of additional protection. Assisted by project partners Buro Happold and the University of Ulster, and with guidance from a Steering Group, a range of such smoke ventilation measures were investigated using Computational Fluid Dynamics (CFD) and reduced-scale physical modelling. Supported also by a review of published research and current practice in the UK and overseas, the project has considered both the initial stages of a fire where occupants would be making their escape, and also later stages where fire fighting operations may have commenced or evacuation from other building stories be required.
The range of smoke ventilation schemes investigated includes external wall ventilators, naturally ventilated smoke shafts, mechanical smoke exhaust from the corridor and pressurisation of the stairway with and without smoke/air relief from the corridor. In both the physical-scale experiments and the CFD simulations the transport of smoke and heat from a dwelling fire into adjoining corridors and stairs has been examined. Provisions for replacement air and the influence of adverse wind and stack pressures was also investigated.
Figure 1 illustrates part of the 1/5th scale physical model, showing smoke travelling along the ceiling of a corridor in one of the experiments. The model also included a stair and lobby section, and allowed a range of natural and mechanical smoke ventilation schemes to be studied.
Figure 2 shows a typical output from BRE's CFD fire model JASMINE, here showing contour plots of temperature for a scenario with a naturally ventilated smoke shaft where some smoke enters the stairwell.
The project has demonstrated that, if exposed to smoke from a dwelling fire for more than a short duration, the adjoining common corridor / lobby can be expected, in general, to become smoke filled. While external wall vents to the lobby / corridor may then in some circumstances maintain tenable conditions inside these spaces, in general an engineered mechanical solution would be required to achieve this. This could be in the form of either a smoke extraction scheme or a pressurisation scheme with protection extended into the common corridors.
If the remit of the smoke ventilation scheme is primarily to offer additional smoke protection to the common stair, then a range of natural and mechanical approaches are suitable. Arguably the simplest and most robust approach is provided by external wall ventilators located in the adjoining common lobby / corridor. The project has demonstrated that a higher level of protection can be provided by a naturally ventilated smoke shaft located in the lobby / corridor. This serves to draw smoke from the corridor and depressurise the corridor relative to the adjoining stair. However, such a smoke shaft arguably requires greater design effort and post-occupation maintenance than an external wall ventilator.
Alternatively, air/smoke can be mechanically extracted from the corridor and, provided replacement air provisions are made, the stair can be protected from smoke ingress. Stair pressurisation, with air/smoke relief from the corridor, provides an alternative means of mechanically protecting the stair. These mechanical schemes can be designed according to non-fire pressure differential and open door air speed criteria, and in general will be more robust with respect to adverse wind and building stack pressures than external wall ventilators or naturally ventilated smoke shafts.
A final report, giving details of the whole project, including the modelling studies and the review, will be available to the public from the BRE website.
Other Articles...
© Copyright 2011 Means Of Escape Terms & Conditions Privacy Policy
Copyright © 2011 Think Agency - Website Designers Kent