Similarly, The National Fire Protection Association defines a high-rise building as:
"A building greater than 75 feet (25 m) in height where the building height is measured from the lowest level of fire department vehicle access to the floor of the highest occupiable story."iv
Yet, most fire departments and construction companies operate on a much simpler and more subjective definition of a high-rise as a building that "is too tall for a fire department ladder truck to access from the outside."v
Threats to High-Rise Buildings
According to Ron Klemencic, the leader of a U.S. group of construction experts formed after the 9/11 attacks, buildings simply cannot be designed to "?withstand inbound airline or missile attacks.?"vi The general consensus among industry experts today is that the WTC towers performed remarkably well on 9/11, having structurally survived the initial aircraft collisions. In fact, many industry experts credit the structural resilience of the WTC towers with saving countless lives by granting the occupants time, although limited, to escape from the buildings before they collapsed.
Hence, the single greatest exogenous threat to high-rise buildings today is a terrorist attack. Taking the form of a missile strike or an explosive detonation, a terrorist attack has the potential to transform a majestic high-rise into a pile of rubble.
A missile attack, whether it be by Rocket Propelled Grenade (RPG) or Man Portable Air Defence system (MANPAD), or simply a hijacked commercial airliner, is impossible structurally to defend against. It is impractical to construct all high-rise buildings with enough structural resilience to withstand a significant missile strike or strikes. And structurally withstanding the initial strike is only half the challenge.
The damage caused by a missile strike is threefold. First, the missile inflicts damage on a structure kinetically by exerting destructive energy in the form of force. Second, the missile inflicts damage on a structure thermodynamically by releasing destructive energy in the form of heat and blast overpressure. And third, the missile inflicts damage on a structure through the creation and spread of fire and any other substance, chemical, biological, or radiological for example, that it is carrying.
Similarly, an explosive detonation, such as by a truck bomb or other device strategically placed within or around a building, inflicts structural damage thermodynamically, in the same way as a missile, and through the creation and spread of fire and other potentially hazardous substances contained within. Historically, truck bombs have been the terrorists? weapon of choice against high-rise buildings: Consider the devastation of the 1995 bombing of the Murrah Federal Building in downtown Oklahoma City, the 1993 bombing of the WTC towers in New York City, and the 2003 bombing of the HSBC bank in Istanbul to name a few.
Missile strikes and truck bombs indeed have the potential to deliver hazardous chemical and biological agents to the occupants of high-rise buildings. However, the immense heat generated by the explosion of a missile or bomb would naturally burn-up the majority of any chemical and biological agent present. Overcoming the laws of physics requires a significant technological capacity and proficiency; one typically not possessed by terrorists. As a result, terrorists have historically chosen to utilize the simple, yet effective, raw explosion to kill civilians.
The by-product of most explosions is fire. A fire can also arise under a number of other conditions and circumstances such as electrical malfunction and human error. Lethal in its production of noxious smoke and gases, searing heat, the speed with which it spreads, and its ability to induce structural weakening and eventual collapse in buildings, fire, in an independent capacity, poses the greatest safety risk to occupants of high-rise buildings today.