High-rise building evacuation
Fire Protection and Life Safety have always been a critical design component for high-rise buildings. With the new peaks of the skyscrapers proposed in Asia, study focused on the high-rise building evacuation is being discussed in order to seek input and feedback for future improvement.
General high-rise building definition is slightly different among countries. In the United States NFPA – it is a building where the highest floor of an occupied story is greater than 75 ft (23 m) above the lowest level of fire department vehicle access. For China, it is for the building over 27 meter of residential building and height over 24 meter of non-single story industrial facility, storages and other civil buildings.
With the increasing height of high-rise buildings, a new definition particularly focus on the skyscraper is addressed as the following:
- TALL – 50M
- SUPER TALL – 300M
- MEGA TALL – 600M
These building height brings more challenges for Fire and Life Safety due to the design features itself as well as the people’s egress behavior comparing with the past after 911.
Separately, for example in China, the fire code has progressively stronger requirements while building height rises, some examples are as the following:
Class 1 high rise-buildings over 24 meters need to be provided with the smoke proof stairwells with pressurized vestibules. This can give the occupants more protected means during the egress and evacuation. Also, fireman lifts need to be provided for firefighting and rescue purpose.
Buildings over 100 meters need to be provided with areas of refuge and roof helipad for multiple fire and life safety concerns and purposes.
Buildings over 250 meters the design needs to be reviewed by a special experts panel for approval with enhanced fire and life safety design features.
One of the significant challenges with all the super tall buildings is the egress and evacuation. Before 911, the evacuation plan was always proposed with the 5 floors for evacuation named defined in place (fire originated floor and 2 floors below and above) Regions and countries like China also have specific requirements for area of refuge. They are stated in the fire code for building over 100 meters that need to be designed with a dedicated floor or shared with mechanical floor with ensured fire separation of providing the assembly area for people as a shelter area before or during the evacuation process. This particular requirement which is primarily seen in Asia in the past have been proposed in the other parts of the world such as Middle East where there is growth in tall buildings. The code changes in US based on the investigation of 911 requires additional interior exit stairway for buildings other than Group R-2 that are more than 420 feet (128 000mm) in building height, one additional interior exit stairway meeting the requirements of code shall be provided in addition to the minimum number of exits required by code . The total width of any combination of remaining interior exit stairways with one interior exit stairway removed shall be not less than the total width required by code. Scissor stairways shall not be considered the additional interior exit stairway required by this section.
Exception: An additional interior exit stairway shall not be required to be installed in buildings having elevators used for occupant self-evacuation in accordance with Code.
So you can see from above, elevators have been introduced and proposed for emergency egress purpose due to the big concern of the extended evacuation time as building heights increase. With the new elevator technology and interlock with fire detection system, new concept of using elevator, called life boat, for egress and evacuation is now formally introduced to the code (IBC, international Building Code) as a tradeoff for providing another dedicated egress stair for fire fighters. For other countries, such as China, the motivation of using elevator for egress is because of the concern for the super high rise which the full building evacuation time will be exceeding 2 hours based on the computer simulation as well as some referred existing building fire drill data. The code requires of 2 hour fire rating of the exit stair enclosure. 2 hours full building evacuation time is becoming the threshold criteria for initiating the special egress design study of a combined elevator assisted egress and egress stairs with computer modeling analysis. This is also called lifeboat egress and has been widely proposed for numbers of representing skyscraper buildings. However detailed study including various proposal including number of the proposed elevators for life boat assisting egress is requested in order to get the most cost effective and fire life safety approved design. As this is changing the traditional concept for not to use the elevator for egress during a fire as world-wide accepted practice, this new approach needs to have a solid program in terms of human behavior and elevator design features to ensure it is a practical solution.
Area of refuge (AOR) for example required in China code for building over 100 meters has been introduced to the life boat full building egress process. Below is a table showing some study result:
You can see the goal here is trying to get the full building evacuation time within 2 hours which is the minimum fire resistance rating for the egress stair enclosure. Considering of the various scenarios, factors including occupancy load, area of refuge area location and proposed associated the loading and unloading place, double deck elevators settings, elevator speed etc. and its impact to the overall egress time and efficiency to determining of the best proposal of the combined stair and elevator egress.
In order to implement the proposed life boat egress program, both reliable software and hardware needs to be carefully designed and reviewed and clearly defined in the building/facility’s emergency planning manual. This is including the following elements for the building:
- Vertical function zones
- Typical floor plan, section and elevation plan drawings
- Egress design floor plan including AOR floor
- Elevator design diagram
- Fire detection alarm and notification system
- Elevator life boat design requirements for the elevator
- Emergency power system design
- Emergency management design
- Special egress program of the combined egress stair and lifeboat
- Human movement characteristics in the stairs and elevators
- Develop a dynamic wayfinding guidance system
Conclusions and recommendations
Opportunities and challenges
- Building height increase promotes fire and life safety importance
- New building construction technology can benefit fire and life safety design
- Building design and construction disciplines working with each other more closely
- Architectural creation unbalanced with the FLS hardware and software
- More human factor dominated outcome
- Public expectation and perception delivers both motivation and pressure to the professionals and the building industry
Past, current practice and future trend
- More risk-informed approach considering building’s nature
- Using reliable building technology for egress planning, design and implementation
- Local practice is contributing to the global design standards
- How high is the Limit?
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