There were five emergency power systems in WTC 7. Three of them (American Express, OEM, U.S. Secret Service) drew fuel from the other two and larger systems (Salomon Smith Barney, Silverstein Properties). (1c), (8)
The emergency power for the building (Silverstein Properties) was provided by two 900 kW generators on the southwest corner of Floor 5. They drew fuel from a 275 gallon tank nearby, and this was replenished by pumps drawing from two 12,000 gallon tanks at ground level under the loading dock, at the southwest corner of the building.
The SSB emergency power system used nine 1,725 kW generators on Floor 5: three in the southwest corner, two near the west end of the north face, four at the east end of the north face. Louvers for air intake and exhaust were situated on the building faces near the generators. Because there was already a 275 gallon "day tank" on this floor, the SSB system pumped on demand from their own pair of 6,000 gallon storage tanks, also situated under the loading dock, under the southwestern part of the building.
The fuel supplier was contracted to keep the tanks full, and they were full that day.
Fuel pipes for all systems except SSB ran up the western side of the core of the building, along elevator shafts. The SSB pipes ran up a shaft through mechanical spaces near the southwest corner of the building.
Kindling
After 1 p.m. on September 11, 2001, WTC 7 was an evacuated, stricken building. The southwest corner and central third of the south face had been ripped open by the cascading debris from the collapse of WTC 1. Fires burned in sections of Floors 6 through 30 at different times, and they migrated along their floors independently, seeking new sources of fuel. From the street the fires on Floors 11 and 12 appeared most intense. Many fires in the area went unchecked because utility power for electrical pumps, and water pressure for fire engines had either diminished or been lost.
This is what happened.
A Pumped Oil Spill
The debris fall ripping into the southwest corner ruptured the oil pipes of the SSB pressurized fuel distribution system. Operating as intended -- the lack of utility power triggering the "need", and the lack of pressure due to a severed pipe signaling the "demand", the SSB system pumped oil up from its 12,000 gallon basement reservoir, maximally with a pressure of 50 psi (pounds per square inch) and flow rate of 75 gpm (gallons per minute), onto Floor 5.
Pumping would have started at 9:59 a.m., when Con Ed cut utility power to WTC 7; and the spilling would have started a half hour later when the pressurized pipe was cut. The SSB pumps could have drained the two 6,000 gallon tanks in 2 hours and 40 minutes. Engineers from the New York State Department of Environmental Conservation found that "there was a maximum loss of 12,000 gallons of diesel from two underground storage tanks registered as 7WTC." (10)
Additionally, "Both tanks were found to be damaged by debris and empty several months after the collapse. Some fuel contamination was found in the gravel below the tanks and the sand below the slab on which the tanks were mounted, but no contamination was found in the organic marine silt/clay layer underneath." (7)
By contrast, 20,000 gallons of oil was recovered from the two 12,000 gallon tanks of Silverstein Properties. (10)
Pulled up by the emergency pumps, the SSB diesel fuel went , from the 6,000 gallon storage tanks, under the loading dock, under the southwestern part of the building, to floor 5.
It may all have been pumped out by 1 p.m., or it may have been pumped out at a rate as low as 29 gpm for 7 hours. Since this fuel was absent from the wreckage, it was burned. You can see it as the huge plume of black smoke rising from the World Trade Center, in panoramic photographs of that day. Diesel fuel can supply 2.13 MW of power per gpm given an air supply of 1333 cfm (cubic feet per minute). (11)
Thus, a diesel fuel gusher of 75 gpm burning with excess air would produce 160 MW of heat; a total energy of 1536 GJ for the 12,000 gallons. This energy is equivalent to that released by an explosion of 367 tons of TNT. If the pumping rate is lower, or the air supply is throttled, then the burning would occur at a lower rate. Since the louver system along Floor 5 was designed to supply each of the nine SSB engines with 80,000 cfm, it seems likely that a fuel oil fire there would find sufficient air for combustion.
For a discussion of heat at 9/11, and energy units, CounterPunchers will soon be able to have my study, "the Thermodynamics of 9/11", to be published shortly on the CounterPunch website as part of our final package on the actual physics and engineering realities of the collapse of the WTC buildings.
This article is a visualization of what probably happened.Only gods and the dead have certainty; we, the living, have rationality and courage to guide us through the puzzles and the perils of life.
When technical accuracy might otherwise require an author to mire his work in a morass of qualifiers, he may choose to preface his work by stating a general qualifier that attaches to the entirety of what follows, the sum and each individual part. In this case, extracting a quote without providing the qualifying preface generates the classic quote out of context.
The author, Manuel Garcia, Jr., qualified his article as being only his "visualization of what probably happened," in his opinion. He explicitly stated that he lacked certainty regarding what happened.
The source used to "support" your claim to certainty in what happened admits he is uncertain and his entire article was only speaking of his perceived "probability."
Where he says, as you quoted, "This is what happened," it is in the context solely of his perception of probability.
Quoting from where the qualifier appears to where AGAviator started quoting, including the first paragraph quoted by AGAviator:
WTC 7 was mortally wounded. In 5 hours and 21 minutes, it would collapse. This article is a visualization of what probably happened. Only gods and the dead have certainty; we, the living, have rationality and courage to guide us through the puzzles and the perils of life.
WTC 7: By The Numbers
WTC 7 was a 176 m (576 ft) tall, 47 story building with a trapezoidal cross section (about): 99 m (325 ft) along the north face, 76 m (249 ft) along the south face, 45 m (148 ft) north-south width, and 47 m (153 ft) along the east and west sides, (4). WTC 7 was about 107 m (350 ft) north of WTC 1, across Vesey Street.
A number of engineering reports have been written about the collapse of WTC 7, because of its uniqueness. A consistent story emerges through the mass of detail. The basic model of the WTC 7 collapse was stated in the earliest report, by FEMA (1c), and increasingly amplified upon by subsequent investigators at NIST -- the National Institute of Standards and Technology, a federal agency within the U.S. Commerce Department's Technology Administration. See footnotes (5), (6), (7) and (8).
WTC 7 was built in 1987 over an existing Consolidated Edison electrical substation. The Con Ed substation was three stories high, and took up the northern half of the footprint of WTC 7. The 1967 construction of the substation accounted for the eventuality of a building above it, and a much larger and stronger foundation was built. Also, a series of columns rose through the area of the substation, for future use.
The design of WTC 7 was larger than anticipated by the provisions of 1967, so additional foundation columns were sunk. Also, the placement of columns in WTC 7 above Floor 7 did not match all the tops of columns connected to bedrock and waiting to be used. Thus, a series of trusses were designed to transfer the vertical loads above Floor 7 and redistribute them laterally to match the waiting columns below Floor 4. This transition used triangular assemblies of structural steel joined into a framework spanning two stories, Floors 5 & 6.
Part of the transition structure included a Floor 5 made of 11 inches of reinforced concrete on top of a 3 inch 18 gage composite metal deck (supported on I beams); Floor 6 was 3 inches of concrete on a 3 inch 20 gage metal deck; the northern half of Floor 7 was 5 inches of reinforced concrete on a 3 inch 18 gage metal deck, and the southern half of Floor 7 was 8 inches of concrete with two layers of reinforcement (no metal deck). Floors 8 and up (except 21, 22, 23) had 2.5 inches of concrete over 3 inch 20 gage metal decks. These metal decks were sheets of metal with corrugations (metal thickness listed by gage number).
The combination of three massive floors and interconnected triangular supports made the framework of Floor 5 to Floor 7 a diaphragm locking WTC 7 together laterally, core columns and walls (encasing elevator shafts and stairwells) to perimeter columns. The construction of WTC 7 above Floor 7 was similar to that of the WTC Towers (9). The irregular framing between Floors 5 and 7 made for less desirable tenant space, but it was well protected by the robust construction, an ideal location for the building's machinery and the emergency power systems.
Machine Space and Emergency Power Systems
Only machinery resided on Floors 5 and 6. Floor 6 had two large cut-outs, one along the east side, another in the southwest corner, to allow for two-story mechanical spaces. A set of louvers spanned the height of Floors 5 and 6 along the eastern face of the building. Table 1 lists the equipment that resided on Floors 5 through 9 (ground level is floor 0).
Table 1, Machinery on Floors 5 to 9, WTC 7
Floor Items
9 1 generator (1 tank) for (tenant) U. S. Secret Service
8 1 generator (1 tank) for (tenant) American Express
7 3 generators (1 tank) for the Mayor's Office of Emergency Management
The "tank" noted in the table would be a 275 gallon diesel fuel tank, the maximum size allowed on any given floor by the NYC Building Code.
There were five emergency power systems in WTC 7. Three of them (American Express, OEM, U.S. Secret Service) drew fuel from the other two and larger systems (Salomon Smith Barney, Silverstein Properties). (1c), (8)