Received wisdom has been that, in general, using lifts in fire emergencies is considered too risky. But following research in the aftermath of the attack on the twin towers in New York, new draft guidance from BRE sets out circumstances where this could be an option.
Buildings in today’s built environment – even those tall and gleaming steel and glass towers in our cities – generally have been designed for evacuation by stairs. In taller buildings, these stairs are usually designed for escaping a limited number of floors at a time – known as phased evacuation. The only real exception to this rule is in the case of lifts designated for firefighter intervention and the evacuation of the disabled. Similarly, underground complexes and subway evacuation is generally by stairs, though London Underground does use escalators.
In the aftermath of the collapse of World Trade Centre towers in New York in 2001, however, designers, engineers and researchers have been asking whether the availability of lifts and/or escalators in appropriate circumstances could improve egress from tall buildings and underground complexes. Some studies since then have indeed indicated that this would allow an improved evacuation time in such buildings.
Specifically, research into the World Trade centre collapse showed that in the 16 minutes before the impact of the second aircraft, 27% of those who evacuated the second tower used the elevators for part of their escape route. The flow rate from tower 2 during this 16 minutes was around twice that for tower 1, where only the stairs were available for evacuation. Other commentators, however, have suggested that from this alone it is not possible to conclude that elevators played a significant positive role. In addition, there is some evidence to suggest that actual rate of people escaping on the stairs was only around 50% of that measured during evacuation drills.
Potential difficulties during the evacuation of the twin towers included obstructions, mobility impairment, illness, fatigue, counter-flow (people and or rescuers going the other way) and footwear that was not suited to walking down many flights of stairs. Approximately 1000 or the 9000 surviving occupants had a limitation that impaired their ability to evacuate, including recent surgery or injury, obesity, heart condition, asthma, advanced age and pregnancy.
The BRE project objectives were to:
– Determine the current methods/modes of operation of passenger lifts and escalators in the built environment.
– Consider the needs of emergency services in using lifts and escalators to access various areas of buildings and underground complexes, and how this may interact or conflict with evacuation.
– Carry out a scoping study on appropriate emergency management and evacuation procedures for a range of events.
– As a further development of the scoping study outlined above, carry out a detailed analysis of different key scenarios.
– Develop models) and then use it them to consider stair, lift and escalator performance under the emergency scenarios identified.
– Identify additional design features and/or management measures necessary to ensure reasonable provision is made for people using the lifts or escalators.
– Develop draft guidance, including appropriate standards on the design and management features needed if their use is to be considered in emergency evacuation and access.
Current practice
The first step was to research the current status of using lifts and escalators in an emergency. The provision of lifts for normal operation in a given building is usually determined by reference to the ‘quantity of service’ – moving a given percentage of the building’s population in a given time – and the ‘quality of service’, i.e. the time between the lift call and when it actually arrives. In the UK, standards governing lift design and installation include CIBSE Design Guide D, BS 5656 Part 2, and BS EN 115.
Evacuation from buildings of people whose mobility is impaired is governed by BS 5588 Part 8, which is currently being revised. Specific types of buildings – such as underground stations and large hospitals – may follow their own detailed codes, while specific tall buildings may have tailored additional measures or procedures.
Studies have shown that using lifts can reduce the total evacuation time by 36%, rising to 56% for the first quarter of evacuating occupants. Other research points to lifts being beneficial in cases of more than eight storeys and that lift capacity, rather than arrangement, is the most important factor in evacuation.
But widening the use of lifts beyond evacuation for just those with mobility impairments is not without its obstacles, not least as it will require a change to the existing mindset and culture of generally avoiding them in fire emergencies. Other potential problems include the somewhat counter-intuitive behaviour of waiting around in lift lobbies in an emergency, coupled with what has been termed ‘learned irrelevance’ which may cause occupants to forget about and so not use the stairs. Another concern would be the possible exposure to fire and smoke if the lift were allowed to open onto the floor of the fire, smoke ingress into the lift shaft, or the failure of any refuge protection. Other potential hazards include overloading a lift preventing it travelling, pressurisation causing door jamming, and power failure. Finally, the feasibility of upgrading existing buildings and the inconsistency of evacuation policy between individual buildings have been raised as concerns.
Potential solutions to some of these hurdles include the provision of refuge floors using dedicated high speed shuttle lifts, lifts stopping at the top call first and not stopping on the way down, and automatic, control room and/or fire service manual control of the lifts. So evacuation using lifts and escalators is feasible but involves significant organisational and engineering challenges.
Outcomes
The outcomes of the project have resulted in draft guidance which sets out the process for considering the use of lifts and escalators. The layout and geometry of the building needs to be considered, and generally tall buildings with large populations, particularly those designed for phased evacuation, would be potentially more suitable. Lower rise buildings, such as airports, shopping centres and subway stations, would also be potential candidates. Needless to say, the process is far simpler for new builds, where these factors can be incorporated during the design process. Existing buildings are a far greater challenge, where considerations could include whether a building’s structure complies with the current Building Regulations. Specific issues with lifts themselves would include:
– Are they ‘collective’ lifts (i.e. can they manage and prioritise multiple calls)?
– Can they include additional modes of operation?
– Do they have a non-stop button or lift load non-stop facility?
– Do they have a voice synthesiser?
– Do they have position/out of service indicators at landings?
– Is their condition monitored?
– Are they in a fire resisting shaft?
– Are they lobby protected?
– Is the lift shaft pressurised?
– Are the lifts protected against flooding?
– Is there standby power supply for all lifts?
– Is power supplied to all lifts from two different substations?
– Is the lift power supply independent of the building power supply, protected and routed up the lift shaft?
The human factor
It’s not just the building and lift systems, however, that need to be considered. The characteristics of the occupants play a big part, such as the density of occupation, the occupants’ knowledge of the building and its layout, and the proportion of people with a disability or impaired mobility. It may be easier to introduce and manage evacuation by lifts and escalators if the layout knowledge of the occupants is good and reaction times are low, and it may be more beneficial to do so where densities of people are high and where there are proportionately more people with impaired mobility.
Location and environmental factors are also key. Considerations include the location of the building and its proximity to fire and rescue service intervention, the type of neighbouring buildings, and the building’s potential vulnerability in terms of its proximity to urban centres and airports etc. Human factors of course play a critical role, so evacuation routes need to be simple and clear. Occupants need to be made aware of escape routes other than the obviously visible ones during evacuation exercises.
Building evacuation strategies generally involve three types: simultaneous, phased, or others such as zoned or progressive horizontal evacuation. Using lifts is unlikely to significantly benefit simultaneous evacuation strategies unless they are from high rise buildings and involve a large number of occupants. But significant benefits with this approach are likely for phased evacuation strategies in office premises. For zoned or progressive horizontal evacuation, this approach is likely to especially benefit large or complex lower rise buildings such as airports, hospitals and shopping complexes, where consideration can be given to the use of lifts in compartments horizontally separated from the compartment of fire.
Just as important as the physical characteristics of a building is the management and control of it and those inside it. Obviously this should not just be about managing an evacuation if a fire breaks out, but should be just as concerned with managing the prevention of fire. BS 5588 Part 12 provides a table showing how different sets of circumstances can be categorised into different management levels, from Level 1 (the highest) to Level 3.
Any proposed evacuation plan by lift or escalator should form part of the integrated evacuation strategy. It should be of an equivalent robustness and provide similar protection as existing provisions do under BS 5588 Part 8 for evacuation of disabled people by lifts. In particular it should not compromise the efficacy of other functional fire safety measures – for example, escalators passing through a compartment floor – or undermine other fire protection systems. In other words, it is expected that the use of such an evacuation strategy should be over and above the normal appropriate means of escape provisions for a given building. The whole point of having such a strategy is to increase the resilience of buildings by speeding up the evacuation rate, not to provide the same results by different means.
This means being prepared to install additional fire safety measures, which could include providing lobby protection to lifts (if not already provided), upgrading lift systems, upgrading fire resistance of elements of a building and improving the building’s communications systems with, for example, public address and/or voice alarms and CCTV. Similarly, a Level 1 fire safety management system should be in place if both staircase and lifts are part of an evacuation strategy, while buildings with Levels 2 and 3 fire safety management should not use lifts or escalators for the emergency evacuation of general building occupants. Level 1 is also recommended if there is more than one strategy for the evacuation of a building; for example, phased evacuation for fire events and simultaneous evacuation for other imminent catastrophic events.
Applications
The guidance is likely to go on to assess the appropriateness of lift and escalator evacuation when applied to specific cases. For example, in an existing building with an unprotected escalator or lift – such as a retail store with a simultaneous evacuation policy – it is probably inadvisable to use passenger lifts and escalators in a fire. But they may be used for an imminent catastrophic event if there are sufficient trained staff on hand. For a well compartmented high rise building with limited emergency stair width or capacity, however, lift and escalator evacuation may be a good option. Table 1 provides a matrix of factors that can affect the benefits and implementation of this.
The guidance is also likely to help quantify the benefits of lift and escalator evacuation by providing equations to calculate estimated vertical flow times and the effect of fatigue. Examples of these are summarised in Table 2. Detailed computational evacuation analysis was undertaken to develop correlations between evacuation time, starting location and the mode of evacuation in a high rise office, and these can provide great insight into the efficiency of an evacuation strategy.
In summary, the research finds that the use of lifts is beneficial in all buildings for people with impaired mobility. But if considering using them for the evacuation of the general population of a building, there are many detailed factors to consider, including the building design, management systems and evacuation procedures in place, and a range of human factors and reactions. For some buildings, such as tall offices and underground station, simultaneous evacuation times may be reduced by between 15% and 50%. For other buildings such as medium rise offices, there is little or even a negative effect in terms of evacuation time. The cases analysed indicate that there is no scope for substituting escape stair capacity with lifts or escalators. So the guidance is likely to proposes a range of additional fire precautions in order to enable such evacuation, but these are likely to be recommendations for voluntary adoption only.
This article is based in a paper given by David Charters at a BRE seminar on the emergency use of lifts and escalators for evacuation.
