Every time we see the horrifying images of the World Trade Centre’s twin towers disintegrating in front of our eyes, we must surely ponder the terror and dread experienced by of those trapped in the buildings in the seconds before they died. It has left a legacy in terms of the challenges of high-rise building safety that are as real today as they were in 2011. And the question is still being asked: “How can people trapped in these buildings be evacuated?”
Achieving safe evacuation from any building is a challenge, but probably not more so than in high-rise structures that today punctuate the skyline of just about every major city across the world. The reality is that designing and constructing new buildings to achieve total safety in the event of a major fire or terrorist explosion is just about impossible; with many existing high-rise buildings the situation is even worse – we have no option but to work to overcome any barriers to safe evacuation that may have been designed-in. The inevitable consequence is that considerable time and energy has gone into devising evacuation and safety solutions that overcome these challenges or at least go some way towards minimising the casualty toll.
However, before deciding on a solution – be it a partial or complete solution – it is important to take a close look at the nature of high-rise buildings and how we behave in them in an emergency. The World Trade Centre tragedy in New York is probably the most researched and analysed evacuation challenge of all time, so what barriers to safe evacuation have been exposed?
Evacuation via a staircase is, in many instances, the only available option. However, the limited capacity of stairs in relation to the potential number of people attempting to escape means that, even if the staircases have not been engulfed in toxic smoke and flames and are a safe exit route, it will soon become gridlocked by an ever-increasing number of people attempting to reach safety. This, in itself will increase panic and may well lead to life-threatening crushes. It will also inevitably deny firefighter access to the fire, potentially resulting in it spreading and entrapping more people in higher floors in the building.
This reliance on stairs for safe evacuation is, of course, even more questionable for any unaided physically or mentally disabled occupants that may be wheelchair-bound, partially sighted, blind or deaf. The problem is not really eased where elevators are still in operation. While some high-rise buildings do incorporate shelter-in-place “areas of refuge” their capacity is limited and, in the case of the World Trade Centre collapses, would have proved to be valueless. In the majority of cases, shelter-in-place facilities still require the occupants to be evacuated at some stage.
Phased evacuation, aided by the use of voice alarm systems, can and does make a valuable contribution towards effective evacuation. This phased evacuation option is, of course, unavailable to those trapped and isolated above the fire – as was the case for many in 9/11 – and, in any event, time may simply not permit the phasing to be fully accomplished before lives are lost. It is worth remembering that, for those lucky enough to escape the World Trade Centre buildings in New York, the mean length of time to descend to the ground for the WTC 1 building was 40 minutes and for the WTC 2 building was 22 minutes.
Evacuation Options.
In an attempt to offset these challenges, fire engineers, architects, developers, owners and occupiers of buildings are looking at alternative options to achieve safe and swift evacuation from high-rise buildings, and a number of solutions are now available. It has to be pointed out however that each solution has to take into account the particular design characteristics of the building for which it is intended.
In some instances, the challenges increase as the number of floors gets greater and as the building gets higher. Some solutions are focused solely on the safe evacuation of single occupants, others on evacuation groups of people, while others still additionally assist the emergency services in delivering firefighters and firefighting equipment to the upper floors of a building.
The available solutions fall into two general categories: equipment for the “internal” evacuation of individuals, and systems for the supplementary external evacuation of greater numbers of building occupants. Equipment designed for “internal” evacuation tends to be aimed at safely evacuating single mobility impaired or handicapped individuals. While this undoubtedly performs an important function, such equipment is not capable of evacuating large numbers of people from a building that, potentially, is at risk of being engulfed in fire or of imminent collapse.
Supplementary External Evacuation.
While there are other systems on the market, such as escape chutes and rescue climbers, the most popular supplementary external evacuation systems generally comprise either controlled decent devises or platform rescue systems. One of the leading manufacturers in the former field is a US-based organisation, High Rise Escape Systems (www.hres.com); another US-based company, Escape Rescue Systems (www.escaperescue.com) is a leading exponent of platform rescue systems.
- Controlled Descent Devices.
Controlled descent devices or CDDs look like, and work in a similar way to a pulley – as one side goes down lowering the building’s occupant in a protective “evacuation suit” that offers flame and heat protection, the other side comes up ready for the next user. This process is repeated until all occupants have been evacuated. The CCD descends at a speed of between one and two metres a second, meaning that a descent from 20 floors up takes around just 60 seconds. They have either portable or fixed-mounted anchoring systems to allow for rapid “pre-planned” or speedy “unplanned” attachment to the structure.
- Platform Rescue Systems.
Platform rescue systems (PRS) move vertically along guides or other means on the exterior of a building and operate in much the same way as an elevator or lift. They are installed inconspicuously on the roof of a high-rise building and, during an emergency, cabins automatically deploy and lower to the street level.
First responders board as they arrive at ground level and control the fire-protective cabins as appropriate for the given emergency. They can deliver up heavy hose loads, fresh air tanks and much needed supplies, while evacuating people on the way down. These systems can evacuate dozens of people from different floors simultaneously, and some can hold up to 30 people in each cabin and incorporate up to five cabins. The system repeats this cycle, transporting firefighters and equipment up and into the building and evacuating building occupants to safety.
A Culture of Safety.
Safe evacuation relies on more than merely having the equipment in place.
Good housekeeping is absolutely essential to ensure that evacuation routes are not blocked, that emergency lighting is in perfect working order, and that there is an accurate head-count of the people in the building at any one time. Signing-in and signing-out may be irksome, but it avoids risking firefighters’ lives seeking for someone that may not even be in the building. Communication is also imperative.
Also important is for the building’s occupants to be fully aware of the evacuation procedures and equipment that is in place; for that, training is vital. It is, with the wisdom of hindsight, astonishing that in “The World Trade Centre Evacuation Study”, Principal Investigator, Robyn R.M. Gershon, stated that 94 percent of the World Trade Centre’s occupants had never exited the building as part of a drill, that 82 percent had never been provided with evacuation plans, and that 74 percent were never provided with written fire safety instructions. He went on to conclude that the factors significantly associated with length of time to evacuate included a low level of knowledge, a lack of emergency preparedness, multiple sources of information, and overcrowding on stairs or in lobbies.
There are lessons there for all of us.
Contact: For further information, go to www.hres.com or www.escaperescue.com
Photographs: HRES 1 (courtesy of High Rise Escape Systems); HRES 2 (courtesy of Escape Rescue Systems);
