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THE WORLD TRADE CENTER FIRES (NOT SO HOT EH?).
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Joined: 06 Mar 2004
Posted: Mon Sep 27, 2004 6:33 am Post subject: THE WORLD TRADE CENTER FIRES (NOT SO HOT EH?).
THE WORLD TRADE CENTER FIRES.
First you need to know that the north tower of the World Trade Center suffered a very serious fire on February 23, 1975. You also need to know that this fire caused no serious structural damage to the tower and that no steel-framed high-rise has ever collapsed due to fire. The following is a report concerning the February 23, 1975 fire.
The February 23, 1975 North Tower Fire.
This 110-story steel-framed office building suffered a fire on the 11th floor on February 23, 1975. The loss was estimated at over $2,000,000. The building is one of a pair of towers, 412 m in height. The fire started at approximately 11:45 P.M. in a furnished office on the 11th floor and spread through the corridors toward the main open office area. A porter saw flames under the door and sounded the alarm. It was later that the smoke detector in the air-conditioning plenum on the 11th floor was activated. The delay was probably because the air-conditioning system was turned off at night. The building engineers placed the ventilation system in the purge mode, to blow fresh air into the core area and to draw air from all the offices on the 11th floor so as to prevent further smoke spread. The fire department on arrival found a very intense fire. It was not immediately known that the fire was spreading vertically from floor to floor through openings in the floor slab. These 300-mm x 450-mm (12-in. x 18-in.) openings in the slab provided access for telephone cables. Subsidiary fires on the 9th to the 19th floors were discovered and readily extinguished. The only occupants of the building at the time of fire were cleaning and service personnel. They were evacuated without any fatalities. However, there were 125 firemen involved in fighting this fire and 28 sustained injuries from the intense heat and smoke. The cause of the fire is unknown.
So now you know that the WTC towers were well designed and quite capable of surviving a serious fire. I repeat that this was a very hot fire that spread over eleven floors. This was a serious fire.
Much was learned from the 1975 WTC fire. In particular, the fact that the fire had not been contained to a single floor but spread to many floors, caused much concern. The points of entry of the fire to other floors were identified and the floors of each building were modified to make sure that this would never happen again. For some strange reason, the modifications failed to preform on September 11, 2001 and again the fires spread from floor to floor.
The 2001 World Trade Center Tower Fires.
Videos of the towers indicate the fires of September 11, 2001, were less severe than your typical office fire. The dark colored soot in the smoke plume indicates an oxygen starved fire. Such a fire will burn well below the maximum 825 deg C (1,520 deg F) that a hydrocarbon fire can burn at when the fuel and air are mixed in perfect proportions. Of course, if the hydrocarbon is mixed in perfect proportions and burnt in pure oxygen rather than air, then temperatures of about 3,000 deg C (5,500 deg F) can be achieved.
Some thoughts about the World Trade Center Tower fires (from various sources).
(1) One complaint is that much of the jet fuel burnt outside the buildings. This was particularly true in the case of the south tower. After the impact nearly all of the jet fuel would have been spread throughout the area as a flammable mist. When this mist ignited it would have emptied the building of almost the entire fuel load, which then "exploded" outside the building. This is exactly what was seen in the videos of the impacts.
(2) If any quantity of liquid jet fuel did manage to accumulate in the building, then its volatility would lead to large amounts of it being evaporated and not burnt (pyrolysed) in the interior of the building. This evaporated fuel would burn on exiting the building, when it finally found sufficient oxygen.
(3) The jet fuel fires were brief. Most of the jet fuel would have burnt off or evaporated within 30 seconds, and all of it within 2-3 minutes (if all 10,000 gallons of fuel were evenly spread across a single building floor as a pool, it would be consumed by fire in less than 5 minutes). The energy, from the jet fuel, not absorbed by the concrete and steel within this brief period, would have been vented to the outside world.
This means that the jet fuel fire did not heat the concrete slabs or fire protected steel appreciably. Large columns such as the core columns would also not heat appreciably, even if they had lost all their fire-protection. Unprotected trusses may have experienced a more sizeable temperature increase. The jet fuel fire was so brief that the concrete and steel simply could not absorb the heat fast enough, and consequently, most of the heat was lost to the atmosphere through the smoke plume.
(4) Even if the fire-rated suspended ceilings and spray on fire-protection from the trusses was removed by the impacts and the trusses were heated till they had lost most of their room temperature strength, we know from the Cardington tests and real fires like Broadgate, that the relatively cold concrete slab will supply strength to the structural system, and collapse will not occur. Remember, that at Broadgate and Cardington, the beams/trusses were not fire-protected. Consider this quote: After the Broadgate Phase 8 fire and the Cardington frame tests there were benchmarks to test composite frame models. Research intensified because almost all the tests had unprotected steel beams (no fire rated suspended ceiling and no spray-on fire retardant) but collapse was not seen .
(5) Since the jet fuel fire was brief, and the building still stood, we know that the composite floor slab survived and continued to function as designed (until the buildings were demolished one or two hours later). After the jet fuel fire was over, burning desks, books, plastic, carpets, etc, contributed to the fire. So now we have a typical office fire. The fact that the trusses received some advanced heating will be of little consequence. After some minutes the fires would have been indistinguishable from a typical office fire, and we know that the truss-slab combination will survive such fires, because they did so in the 1975.
(6) Of course, most of the weight of the building was supported by the central core columns. There is no indication as to how these 47 massive columns might have failed (at least in the case of the north tower, some of these columns, perhaps two or three, would have been displaced by the impacts). We know that the jet fuel fire was too brief to heat them appreciably. Since the central core area contained only lift shafts and stairwells, it contained very little flammable material. This meant that the core columns could only have been heated by the office fire burning in the adjacent region. Consequently, the core columns would have never got hot enough to fail. But we already know this because they did not fail in the 1975 WTC office fire.
(7) Also, the building engineers placed the ventilation system in "purge mode." This forced fresh (cool) air into the core area keeping it free of smoke and hot gases.
(8) You should consider that it has been calculated that if the entire quantity of jet fuel on the aircraft was injected into just one floor of the World Trade Center, that the jet fuel burnt with the perfect efficency, that no hot gases left this floor and that no heat escaped this floor by conduction, then the jet fuel could have only raised the temperature of this floor to, at the very most, 257 deg C (495 deg F). You can find the calculation here.
(9) Another reason that we know the fires were not serious enough to cause structural failure, is that witnesses tell us this. The impact floors of the south tower were 78-84. Here are a few words from some of the witnesses:
Stanley Praimnath was on the 81st floor of the south tower: The plane impacts. I try to get up and then I realize that I'm covered up to my shoulder in debris. And when I'm digging through under all this rubble, I can see the bottom wing starting to burn, and that wing is wedged 20 feet in my office doorway.
Donovan Cowan was in an open elevator at the 78th floor sky-lobby: We went into the elevator. As soon as I hit the button, that's when there was a big boom. We both got knocked down. I remember feeling this intense heat. The doors were still open. The heat lasted for maybe 15 to 20 seconds I guess. Then it stopped.
Ling Young was in her 78th floor office: Only in my area were people alive, and the people alive were from my office. I figured that out later because I sat around in there for 10 or 15 minutes. That's how I got so burned.
Eagar claims temperatures were hot enough to cause the trusses of the south tower to fail, but here we have eye-witnesses stating that temperatures were cool enough for them to walk away.
Interestingly, a tape of radio conversations between firefighters exists (but only relatives of the dead men have been allowed to hear it). Kevin Flynn, of the New York Times, reported:
Chief Orio Palmer says from an upper floor of the badly damaged south tower at the World Trade Center. Just two hose lines to attack two isolated pockets of fire. "We should be able to knock it down with two lines," he tells the firefighters of Ladder Co. 15 who were following him up the stairs of the doomed tower. Lt. Joseph G. Leavey is heard responding: "Orio, we're on 78 but we're in the B stairway. Trapped in here. We got to put some fire out to get to you." The time was 9:56 a.m.
So now we know that, just a few minutes before the collapse of the south tower, firefighters did not consider the fires to be that serious, and were in fact able to get right into the impact region without being killed by the heat that was (according to Eagar) so intense that the trusses glowed red-hot and failed.
(10) Another reason that we know the fires were not as serious as claimed, is that there are photos of people in the impacted region after the planes hit the building (and before it collapsed). The above photos show at least two survivors of the impact and the initial jet-fuel fire.
This photo is an enlargement of the second of the above photos. It clearly shows a women trying to see what is happening on the street below. It is also possible that the brown area to the left may be another women lying on the floor and looking down, but the picture resolution does not allow a us to be sure. An enlargement of the picture of the male survivor is presented on the left below. Initially, we thought that the images had been doctored and the survivors added with Photoshop, but it turns out that the picture of the woman actually appears in the FEMA report (page 18 of Chapter 2: WTC 1 and WTC 2). I have enlarged the relevant section of that photo and circled the woman. The enlargement of the FEMA report photo is presented below on the right, but you should go to the FEMA report and check for yourself.
(11) When fully developed fire conditions (temperatures of over 700｡C) are reached, this results in the breaking of window glass. For example, the 1988 First Interstate Bank fire in Los Angeles, which showed greater heating effects over larger regions than those observed in either tower, rained broken window glass down on the streets below, presenting a considerable hazard to those on the ground. The First Interstate Bank did not collapse.
(12) If the temperatures inside large regions of the towers were of the order of 700｡C, then these regions would have been glowing red hot and there would have been visible signs of this from the outside. Even pictures taken from the air looking horizontally into the impact region show little sign of this.
(13) Another reason the fire would not have been as hot as your typical office fire (at least on the impact floors) is that cross ventilation would have cooled it somewhat. Consider the quote: Cross ventilation resulting from (broken) windows present in opposite walls causes a high intake of air and cooling effects .
(14) If there had been severe fires burning in the core region this would have made the stairwells impassible. However the stairwells below the impact region on the North Tower were sufficiently clear to allow some occupants close to the impacted floors to escape and to allow firemen to reach at least the floors around the 70th level. In the South Tower, at least one stairwell remained operable as there were survivors from above the impact region.
The "Raging" Fires At WTC Tower Seven.
Below is a picture of the "raging" fires at WTC 7, moments before the collapse (it should be noted that the smoke in the background, behind WTC 7, is mainly from the fires in ruins of WTC 1, 2, 3, 4, 5 and 6).
You can be forgiven for not being able to find the fires. To help you out, we present some closeup photos.