It is important to note that elevator shafts, like stairwells, are vulnerable to smoke contamination as well. Due to both the Stack effect and the Breaking-of-the-Seal effect, smoke penetrates into both the elevator carriages and shafts during a fire. Additionally, when elevator carriages are forced to make stops on smoke filled floors, both the elevator shaft and the carriage itself can quickly become contaminated beyond usable limits.
The most common vulnerability found in high-rise buildings today, however, is in the Heating, Ventilation, and Air Conditioning systems (HVAC). The design of most HVAC systems inadvertently amplifies the Stack effect and defeats compartmentalization measures:
"[The] central air system in a high-rise building interconnects 10 to 20 floors for the purpose of heating and cooling. Ducts, shafts, and poke-through holes penetrate fire-resistive floors, walls, and ceilings. These air-conditioning openings and holes allow fire and smoke to spread throughout the 10 or 20 air-conditioned floors of a high-rise building."xii
With the HVAC system?s design inadvertently aiding the rapid spread of toxic smoke to the upper floors and stairwells of a building, not only are the occupants? chances of safe egress further reduced, but as the floor itself becomes heavily contaminated with smoke, the occupants? total chance of survival diminishes significantly as well.
Hence, due to both the design flaws inherent in high-rise buildings today and the inadequateness of their primary evacuation methods, occupants cannot rely solely on their building?s stairways or elevators for safe egress.
Case Study #1: Garley Building Fire, Hong Kong (1996)
During welding work in an elevator shaft in the basement of the 16-storey Garley Building in Hong Kong, highly flammable materials ignited and caused a fire that travelled up the elevator shaft and rapidly spread throughout the top three floors of the building.xiii Because the building?s windows could not be opened to let the heat and smoke out, and because the stairways were heavily contaminated with smoke or impassable due to the fire, 39 people were killed, 22 of which were found charred in a single office on the 15th floor, and 80 people were seriously injured.13
Case Study #2: Meridian Bank Building Fire, Philadelphia (1991)
When a pile of linseed soaked rags left by a contractor on the 22nd floor of the 38-storey Meridian Bank Building ignited, it precipitated a massive 12-alarm fire that eventually brought 51 engine companies, 15 ladder companies, 11 specialized units, and over 300 firefighters to the scene.10
With a "well-developed" fire existing on the 22nd floor, fire spreading via the stairwell down to the 21st floor, and heavy smoke contamination of the stairwells and floors immediately above the 22nd floor at the time when the fire department arrived, the situation for occupants still remaining on the floors above the 22nd looked grim. So severe was the smoke contamination in the stairwells above the 22nd floor that three firefighters tragically lost their lives when they became disoriented and could not find their way to fresh air before their air supply ran out.10 An eight member rescue team launched to recover the three fallen firefighters also became disoriented in the thick smoke and ran out of air as well. Luckily, however, they were rescued by another team and sustained only moderate injuries.10
After an eleven hour firefighting effort failed to bring the blaze under control, firefighting efforts in the interior of the building were suspended due to the risk of structural collapse. However, the fire was controlled when it reached the 30th floor and the automatic fire suppression system triggered.10
Miraculously, the only fatalities resulting from this fire were the three brave firefighters who succumbed to smoke inhalation after they became disoriented and ran out of oxygen. By demonstrating the difficulty and danger that smoke contamination poses to firefighters, this case study illustrates the insurmountable feat that an evacuation, under similar conditions, would be for an occupant. Thus, this case study is a perfect example of how the primary evacuation methods of today?s high-rise buildings are simply inadequate at providing occupants with a safe and reliable means of egress.