The World Trade Center Bombing:
Report and Analysis
Provided by Fire Engineering / FEMA
http://www.interfire.org/res_file/pdf/Tr-076.pdf
These are just two interesting sections that I picked up at a quick glance of the doc. There are a least a few more gems to be mined here.
Sprinkler system. The design of the sprinkler system in both towers is similar. Generally, the direction of water flow in the risers is downward.
There are three separate risers in each tower, with each riser serving
different groups of floors.
The risers are designated A, B, and C. Riser A supplies the uppermost floors, 99 through 110; riser B supplies floors 32 through 98; and riser C supplies floors 1 through 31. The risers pass through the floors in the service closets on each tenanted floor and deviate from plumb vertical only as required by changes in building construction at various evations.
Two different capacity holding tanks - 10,000 gallon and 5,000 gallon - are used in the same sprinkler system. The 10,000-gallon tanks supply the sprinkler system exclusively and are located on the 110th floor; the 5,000-gallon tanks serve both the sprinkler and fire standpipe systems and are located on the 110th and 42nd floors.
The sprinkler tanks supply water to inlets of risers A and B and are automatically refilled by the domestic water system via float-control valves. The fire standpipe tanks supply water to risers A, B, and C and normally are also refilled by the domestic water system. Riser C in 1 WTC is crossconnected with riser C in 2 WTC via a four-inch pipe from the Siamese connections. The function of the cross connections is to provide FDNY with the capability to supply water to the C risers in both towers and control their pressures.
The sprinkler centrifugal pump in each tower on the 108th floor has
a dual purpose. Its main function is to increase the pressure of the water
to the sprinklers on the floors closest to the holding tanks (floors 107 to
99) to that required for operating the sprinklers. However, the pump also
is used to supply water to some of the fire hose racks (FHRs) on the 110th floor.
As the downward distance from the holding tanks increases (floors
98 and below), the pressure (head) of the water in the risers increases to
the point where the additional pump pressure is not required.
The rest of the complex -namely, the subgrade levels, 5 WTC, and
4 WTC - is part of a second sprinkler system completely separate from the one of the towers. This second system consists of a large loopmain with risers going down into the subgrades and sublevels and rising up in 5 WTC and 4 WK.
more....
Why didn't this system have any effect on the fires that did break out? One plane wiped out almost the whole system in each building?
Vulnerability of Buildings to Blast
Damage and Blast-Induced Fire Damage
by Ronald J. Massa
The popular conception of an explosion, as depicted in TV action movies, generally is more dramatic than accurate. The big fireball, resulting fire, and apparent chaos at the blast scene do not accurately characterize the high-explosive detonations of materials such as TNT or C-4.
First, building fires usually are not a dominant effect of high-explosive detonations. If the detonation occurs outdoors, in a well-ventilated area, the hot gases from the initial detonation rarely ignite anything, although they can cause charring of nearby materials. If an explosive is detonated outside but in a car (i.e., a car bomb), the result will depend on the size of the explosive. The expanding hot gases from smaller (lower charge weight) explosive detonations will ignite flammable materials in the car, such as upholstery, fuel, and tires. The smaller explosive charges will do less mechanical damage to the car and often will result in a concentrated fire within the confines of the vehicle. As the charge becomes larger, more mechanical damage will be done to the car, and fire effects will be less concentrated. For example, expanding gas pressure will propel the engine and transaxle apart from the rear axle and wheels, and relatively small fires will appear as a number of the car’s components come to rest at (perhaps) widely separated locations.
Unless the detonation is specifically designed to be incendiary, only locally available combustible materials will be ignited. The particular difficulty with explosion-induced fires is that ignition can occur at almost the same time at widely separated locations because the hot gas cloud expands and propels ignited or ignitable objects away from the center of the blast.
Building fires generally are not an issue when explosive detonations occur outside of buildings. And except in cases where detonations are incendiary in nature, building fires generally are not a major issue when detonations occur inside of buildings. Interior explosion-induced fires generally are caused when something within the building is ignited by the explosion. The problem is like the ignition of gas lines in an earthquake - the earthquake’s mechanical effects themselves do not directly cause fires.
When the detonation occurs inside a building and in a confined and fuel-rich space, such as in a parking garage, the hot gases from the detonation cannot expand freely to mix with an ever-increasing volume of cooler air. The shock effects and mechanical damage from the explosion will overturn vehicles, fracture gas tanks, break pipes, and breach walls, exposing a variety of materials to the hot gas cloud. Many of these will ignite, generally on the periphery of the affected space, where the expanding gas causes the least local oxygen deprivation.’ Thus, suddenly the detonation will spawn many separate fires. From that point on, the building will respond as it would had each of the fires been set with a match. However, if the building were severely damaged by the blast, life safety systems may be incapacitated, gas lines severed, and electrical systems disturbed, all of which will increase the fire vulnerability of the building.
All things considered, while severe explosion-induced fires are unlikely from exterior detonations, interior detonations, particularly those in confined, fuel-rich spaces, frequently result in fires that are exacerbated by damaged building systems. Whether inside or outside, blast effects such as shock waves, expanding gas, and heat frequently dissipate within a second.2 Discreet fires ignited in this interval generally will require a much longer period (typically several minutes) to become serious building fires.
Unfortunately, there are other adverse factors to consider. Ignition at many locations simultaneously and damaged life safety systems already have been mentioned. But the blast also may blow out windows, providing undesirable venting to the fire. If the detonation is a “dirty” one, using a low explosive or smoke-producing components, toxic smoke can be rapidly propelled throughout the structure, creating an instant, additional hazard to building occupants at locations where they are safe from the direct effects of the blast.
Sounds like even you dove a plane into the building and even if it blew up inside of the building, the results would be more shock and awe and the fires would have been relatively small and certainly not enough to cause the complete failure of the structure less then 2 hours later. Unless you blow up something in a fuel rich environment, like a parking garage. Interesting.
