Building Exit Strategy
By John K Y Ng | Submitted On August 01, 2007
Emergencies in high-rise buildings can arise from numerous factors including man-made, weather-related, building system failure, and terrorist acts. In these emergencies, the presence of sprinklers will not control the emergency. These emergencies might require a total or partial building evacuation. But when a tall building has over fifties occupied floors; many questions and concerns have been raised regarding the difficulty of evacuating hundreds or even thousands of people and their safety. This article summarizes the importance of building exit strategy to ensure that everyone would have the equal opportunity to get out in the event of an emergency that requires total building evacuation.
Building Evacuation
If there is an evacuation called for, it is the stairways that will be used by all occupants. Unless damaged by fire or made untenable due to smoke or fire, the interior stairways provide the most stable and least threatening path to the outside and safety. Mobile occupants who are not incapacitated by the fire can safely walk to safety using the interior stairs with little assistance from fire fighters. Immobile or incapacitated victims will require assistance in using the stairs and may need to be carried out of the building.
In extreme emergencies, everyone would have to get out quick and the whole building would need to be emptied in the shortest possible time. But when a tall building has over fifties occupied floors; the sheer numbers of people make evacuation difficult as it takes more time for occupants to evacuate by using the stairs. Hence it is imperative that adequate egress capacity and exit strategy must be available for any emergency, not just fire. Building size, population, function, and iconic status should be taken into account in designing the egress system.
Historically the used of elevators by occupants as a means of escape under fire conditions are considered to be hazardous and should be avoided. However with "mega" high-rise buildings now exceeding 400 meters (1,312 ft) in height, full evacuation for thousands of people utilizing stairs alone would appear to be problematic, especially if the needs of the mobility challenged are taken into account. Some fire safety professionals believed if an elevator is remote and separated from the fire area with an auxiliary power supply, it could be used for rescue purposes under the fire department's control, especially to evacuate immobile occupants.
Most buildings are not equipped with fire escape for alternative means of egress. People are entrapped in blazing tall buildings if the main egress path is cut off and they are beyond the reach of the fire department's aerial devices. In such extreme situations and if the conditions permit, the only rescue option left is to use helicopter to airlift people from the roof. However, this is a very dangerous attempt and the least preference tactic. The rising smoke and the intense heat from the fire could cause the rotor of the helicopter to explode.
Lessons Learned From WTC Evacuations
There are lessons to be learned from any disaster. The World Trade Centre tragedy demonstrated the particular vulnerability of high-rise buildings during an emergency evacuation.
In 1993 a massive bomb was planted in the parking garage of the World Trade Center. Medias reported that there were no emergency lights according to survivors. Some people, including a pregnant woman, were evacuated via rooftop helicopter landings. Most, if not all, of these people emerged with their faces blackened with soot from the thick, acrid smoke in the darkened fire stairs.
One occupant, so the story goes, was wheelchair-bound and couldn't navigate the stairs. People are always told NOT to use elevators in a fire, so he couldn't go that route either. Rather than leave their friend to his death - two other occupants hand-carried him 51 flights down to the street - with one of the carriers suffering a heart attack.
Apparently it took a full seven hours to evacuate all the occupants. This was unacceptable to most people - especially those who occupied the towers.
Following the terrorist attacks on the World Trade Centre on 11 September 2001 where many of its occupants had no time to escape before the towers collapsed, the National Institute of Standard and Technology (NIST) estimate of how many people might have died if the building had been fully occupied when the planes struck at the WTC: 14,000 rather than 2,749 - that should be a cause for everyone to recognise the value in improving the odds of surviving a major fire in a high rise building, regardless the cause.
With egress access identified as an impediment to speedy evacuations, stakeholders must anticipate the need to rapidly escape; plan primary and alternative escape routes if the main egress paths could become unavailable. Failure to develop an exit strategy is a key factor in many large loss fires.
Recommendations
Following the investigations conducted under the National Construction Safety Team Act, one of the recommendations in the National Institute of Standard and Technology (NIST) World Trade Center (WTC) collapse Report for the improved in building evacuation system designs is that all high-rise buildings over 20 stories be designed, or existing structures be reviewed for retrofitting, to accommodate timely full building evacuation of occupants due to building-specific or in large scale emergencies. The recommendations include facilitate safe and rapid egress, methods for ensuring clear and timely emergency communications to occupants, better occupant preparedness for evacuation during emergencies, and incorporation of appropriate egress technologies, which may allow all occupants an equal opportunity for evacuation and facilitate emergency response access.
A new proposal addressing supplemental evacuation equipment has been introduced for the 2009 editions to NFPA code changes for high-rise buildings. It is intended to provide guidance to building owners and others considering the voluntary use of such systems and equipment for exit strategy. If provided, the evacuation equipment is intended to serve in a supplemental capacity and will not satisfy any code requirements pertaining to means of egress. While the proposal is not specific to high-rise buildings, it is expected that such evacuation equipment would be considered for tall buildings.
To comply with these recommendations, tall buildings would need to incorporate life safety features that are beyond the code-required minimum to assist the building staff in implementing the appropriate crisis response evacuation plans that address the life threatening conditions of a tall building emergency to protect both the building occupants and firefighters.
Fire Escape Chute - An Alternative Means Of Escape
There was a program on Discovery Channel named 'Beyond 2000' (out of Brisbane Australia), showed how hospital staff ran a drill wherein they evacuated bed-ridden patients from upper floors via what appeared to be a long stocking, suspended outside the building from a dedicated window/door. This long stocking is a "life saver" device commonly known as fire escape chute.
This escape chute can be installed in the tower from window, rooftop, served as lifeboat to increase egress capacity; in dedicated fire-hardened shafts, so that everyone could escape within an hour - an advantage for disabled people to escape on their own. For controlling the descent down the chute - user merely stick out their elbows/knees. They're typically made of Outer layer: 100 % fiber glass fabric (flame resistant); Middle layer: modacryl / elastomer; (restraint / control the speed of descent); Inner layer: aramid / rhovyl (supports the whole weight of the chute).
Escape chutes are not required by any of today's building or fire codes, making their use voluntary and at the discretion of building owners. However, there is an increase in the use of escape chute at buildings and high-hazard industrial worldwide. They are recognized by many fire authorities as a hardware solution to correct egress deficiencies and to increase egress capacity in old buildings where it is not possible to provide exterior fire escapes or increase the size of existing stairways in its structure.
Think about it. If fire escape chutes is available in multi-story buildings as an alternative means of escape, it can provide a relatively safe means of egress for many people. Given the opinion that elevators/lifts are unsafe for fire egress, stair travel is taxing and potentially dangerous for the aged and the physically impaired; evacuation via escape chutes provides a means of egress available to all people.
Building occupants are generally familiar with the location of the fire escape chutes. Fire fighters should expect to find occupants attempting to use the fire escape chutes when the stairways are untenable. And, even though for many occupants the fire escape chutes is a more threatening egress path, these same occupants may use the fire escape chutes as their first preference due to proximity even if the stairways are clear of smoke, especially for the mobility impaired.
Fire escape chutes would also make the firefighters' job a whole lot easier and safer. Instead of leading/carrying people down several floors in high-rise buildings and simultaneously fighting a fire - people could escape on their own - freeing firefighters to fight the fires.
In fact, because people could get out on their own - the firefighters, would have exclusive access to the fire stairs to get up and a rapid avenue to escape to the street should they need it. How many times have firefighters rank and file needed climbing ropes and gear to rappel down the outside of buildings because those buildings were no longer structurally sound?
Carrying some 100lbs of gear up the stairs means firefighters have to carry it down again as well. How much bottled air can they carry (in their self-contained breathing apparatus) to sustain them both up and down? Firefighters do have a better chance of surviving if they could merely jump into a chute to escape rather than feel their way down smoke-choked fire stairs.
Conclusion
Currently, buildings are not design for the "worst of the worst" on the likelihood of the event and its consequences for any threat or hazard scenario, including hurricane, flood, tornado, earthquake, or fire. Should future high-rise buildings be designed to protect against the most frequent and likely extreme events utilizing redundancy, reliability, and tenability?
Disasters cannot be prevented, but preparedness can minimize the damages and losses that caused by disasters. The World Trade Centre towers in New York were emptied thrice in three decades: on 9/11, the 1993 bombing, and the 1977 bomb threat. Better occupant preparedness for evacuation during emergencies, and incorporation of building exit strategy, would allow all occupants an equal opportunity for evacuation and facilitate emergency response access.
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