Concerns are growing about a disconnect between fire safety design assumptions and performance in real-life situations
The Regs: Geoff Wilkinson examines the move towards evacuation lifts in tall building fire escape strategies
The recent trend for high-rise buildings in London asks many questions about the appropriateness of planning and building regulations, not least whether our current approach to evacuating them is correct.
Ask anyone with a basic understanding of means of escape and they will probably tell you that a building should be evacuated within three minutes and that the lifts must not be used in case of a fire. That is not feasible if the building is 20 plus storeys - never mind the 50 plus storeys of many currently in for planning approval.
The traditional strategy within high-rise buildings is to incorporate high levels of compartmentation, combined with smoke ventilation. This allows designers to adopt phased evacuation techniques where only those immediately at risk evacuate, while others remain safe on the non-fire floors. This means that stairs can be designed to accommodate relatively small numbers of people, taking up less floor space, which is of course at a premium in a tower building. There is also a trend to utilise fire-engineered solutions such as smoke shafts, pressurisation or depressurisation as an alternative to traditional smoke ventilation; again saving space.
However, concerns are growing that there is a disconnect between fire safety design assumptions and how these buildings perform in real life. The 2009 Lakanal House (pictured) fire which saw six deaths and 20 serious injuries, showed exactly what can go wrong if the escape strategy is not understood, maintained and communicated to the building owners and tenants.
There is also the issue of what happens if a tower building needs to be fully evacuated, for example in case of a bomb threat?
The 9/11 evacuation of the World Trade Centre was the largest full-scale emergency evacuation of modern times - requiring the evacuation of some 17,400 people. The evacuation was generally considered a success as ‘only’ 12 per cent of building occupants failed to escape. Furthermore, of those that failed to escape, it is estimated that 3 per cent perished on the impact floors, leaving approximately 9 per cent who survived the impact but were unable to evacuate. Studies into the evacuation, however, suggest that there were still a number of issues which hampered evacuation. These included wayfinding (people did not know the location of emergency stairs), escape speeds on stairs (significantly lower than fire engineers assumed) and the time required to empty a fully occupied building (modelled evacuation times exceeded two hours).
So what is the answer to evacuating these buildings? Current thinking is moving towards the wider acceptance of evacuation lifts as a way of getting people out of the building in the quickest possible time. Regulations already allow the evacuation of disabled people using fire-fighting lifts - see cls 46.9 of BS9999. If such lifts are suitable for disabled people then why should not lifts be used by able-bodied people as well?
BS 9999 indicates that a lift to be used for evacuation needs to be designed and installed in accordance with the relevant provisions in BS 8300, BS EN 81-1 or BS EN 81-2, and BS EN 81-70. However, it goes on to say that a fire-fighting lift, and even in some circumstances a lift not designed for evacuation, may be usable too.
This thinking is likely to be adopted formally in the next revision of Part B due out in 2016, which could theoretically lead to stairless buildings. In the meantime, those working on tall buildings, or those interested more generally in lift evacuation strategies, should consider attending the 2nd International Conference on Tall Buildings Fire Safety on 17-20 June at the University of Greenwich, London. www.bcptesting.com
Geoff Wilkinson is managing director of Approved Inspectors Wilkinson Construction Consultants