Leslie Robertson, chief structural engineer of the World Trade Center in New York, discusses the collapse of the WTC on KGNU Community Radio, Boulder, Co., on the fifth anniversary of 9/11 with physicist Steven Jones. In the fall of 2006, amid controversy surrounding his work on the collapse of the World Trade Center, Jones was relieved of his teaching duties and placed on paid leave from Brigham Young University. On October 20, 2006, he announced his retirement.
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The Myth of Controlled Demolition Theories
It is amazing to me how many Engineers cannot understand how the Towers could collapse from fire. WTC 7, a high-rise office building was not hit by any planes and was destroyed by a fire in ordinary combustible furnishings. You may say it’s highly unreasonable to believe that 4 steel constructed high-rise buildings collapsed from fire in one day? Well they all had one thing in common; Long Span steel composite floors with connections not designed for thermal effects. They designed these buildings to maximize office space while maintaining exterior views and providing office layout flexibility and the interior columns were interfering and had to be removed. This column removal was attained by using long span steel beams and girders which are used in many existing office high-rise buildings. The use of long floor spans along with the 1968 building code relaxation lowering the fireproofing requirements have apparently created a condition that with large fires in these buildings could lead to a major collapse. Long span steel beams have a magnified response to heat. They expand a longer distance than short span beams and they still have their full strength in the beginning of the expansion. NIST computer studies show that this strength while the beam is elongating can shear off the bolts connecting the beams to the columns or girders if the connections are not designed to counter this effect. This strength as the beam expands can also crack the concrete slab at the shear studs and buckle the beam itself as differential internal compression builds up in the steel during expansion. A buckled or bowing long span (over 40 feet) beam can impart large tension forces on the connections especially when a sagging beam begins to shrink as it cools. Bowing occurs when the bottom flange of a steel beam expands faster than the top flange. Bar joist floor bowing places immediate pull-in tension on the connections.
The performance of the floor/beam systems in such buildings has been attributed to a complex interrelated sequence of events, described rather simply as follows (Buchanan 2001):
1. The fire causes heating of the beams and the underside of the slab.
2. The slab and beam deform downwards as a result of thermal bowing.
3. Thermal expansion causes compressive axial restraint forces to develop in the beams.
4. The reaction from the stiff surrounding structure causes the axial restraint
forces to become large.
5. The yield strength and modulus of elasticity of the steel reduce steadily.
6. The downward deflections increase rapidly due to the combined effects of the
applied loads, thermal bowing, and the high axial compressive forces.
7. The axial restraint forces reduce due to the increased deflections and the
reduced modulus of elasticity, limiting the horizontal forces on the
surrounding structure.
8. Higher temperatures lead to a further reduction of flexural and axial strength
and stiffness. (NISTIR 7563)
9. The slab–beam system deforms into a catenary, resisting the applied loads
with tensile membrane forces.
10. As the fire decays, the structural members cool down and attempt to shorten in length.
11. High tensile axial forces [pull-in] are induced in the slab, the beam, and the beam connections.
These actions can take place in two or three dimensions
Photo of Steel structure after Cardington tests in the UK
Use of Steel in Construction
Steel has always had a stability problem under fire conditions. Steel members begin to expand immediately when heated and internal thermal stress in the beams, girders, or joists bends, buckles, twists, and warps the steel, eroding structural integrity. Thermal expansion in a long span beam can shear off the bolts connecting the beam. Thermal contraction in a sagging, long span steel beam can tear out the connections as the beam cools. From a collapse potential the long span, bar joist trusses used in the Tower construction was a most vulnerable design. It was evident from the bowing inward of the exterior columns that the sagging trusses pulled-in these columns on the long span side of each building beginning the progressive collapses. There is also evidence that the collapse timing corresponded with the time to heat these steel trusses,- depending on the insulation thickness used in each tower,- to a temperature which expanded the steel enough to collapse the trusses or cause thermal bowing where the lower truss chord expands allowing the top chord to go into suspension, or upon cooling of the sagging contracting trusses pulled in the exterior column walls .
UK engineer Dr. A.S. Usmani, et al., related the following relative to his preliminary findings about the collapse of the WTC Towers: 5
Due to their length and slenderness, the thermal expansion effects in long-span, steel bar joists produce compression buckling in floors at lower temperatures than are presently compensated for in the fireproofing codes. This sort of thing has not been considered in the design of high-rise structures, with the possibility of multiple-floor fires.
Longer-span steel structural members expand a greater distance than short-span elements, and, as they are heated, slender elements can fail from buckling under compression at temperatures that are still low enough (400° to 500°C) that the steel retains most of its strength.
According to S. Lamont et al “The furnace test does not consider vial structural phenomena found in the 3D behavior of real buildings including large deflections, restrained thermal expansion and thermal bowing, membrane and catenary load carrying mechanisms in slabs and beams respectively, and compatibility of deflections in two or more directions in an integrated structural frame,”41
Expansion Effects
The wider floor sections of the Towers had longer 60 foot joists, which, because of increased loads, would be inherently weaker and would expand and lengthen a greater distance if exposed to heat. Note: “Steel will expand .06 percent to .07 percent in length for each 100°F rise in temperature. Heated to 1,000°F, a steel member will expand 9½ inches in 100 feet of length.” 21 According to the FEMA, ASCE- Building Performance Study, “an unrestrained, 20-meter-long [about 60-foot] steel member that experiences a temperature increase of 500°C [1,022°F] will expand approximately 110 mm [4.0 inches].”18 Note: Steel expansion begins immediately as the steel is heated and can be destructive to the long span trusses even though the steel temperature is low enough (300 to 500 C) that the steel retains most of its strength.
“Differential expansion of steel is probably the main cause of failure of the floor system used in the towers. Since the top chord of the long-span truss is steel, it will elongate more than the top concrete slab at the same temperature. Steel, if not adequately insulated, will also absorb heat faster than concrete. Steel differential expansion has been shown to be a cause of bowing, shear-induced buckling of the struts and the loss of composite action in the floor system [as a result of] the shear ‘knuckles’ detaching from the concrete. The knuckle bonds sequentially break, starting at the ends, eliminating the composite action under load. “(NIST, 2, Appendix K):
Current practice is to protect the steel by requiring enough insulation to prevent loss of strength by preventing columns from reaching 1000 deg. F (538o C) and beams from reaching 1100 deg. F (593o C) in the standard furnace test. This criterion has proven effective in short span designs. As the steel is heated further and temperatures rise to higher than 600°F, steel loses strength. At 1,200°F (about 650°C), steel loses about 50 percent of its strength. At 1,300°F (about 700°C), the yield point is drastically reduced and steel members fail. The collapse of Building 7 and the Twin Towers has been proven that this protection requirement (i.e. 10000 F. for columns and 11000 F for beams) inadequate when protecting long span steel floors since the expansion effects in steel beams can buckle the beams or fail the connections at lower temperatures (400 to 5000 C). Long span steel must now be protected from heat by adequate fireproofing insulation and integrated properly to compensate for the lower temperature effects of thermal expansion and contraction during fires. To maintain building stability, lateral bracing becomes even more important in construction that features lightweight, long-span floors. All three buildings relied on floor membrane stability to laterally support the columns.
The fireproofing insulation thickness schedules in the Building Code were developed for the short span floors which were used in the older high-rise buildings and this insulation defended against thermal weakness in the steel beams rather than expansion which apparently was not a problem in the shorter spans. Steel weakening occurs later at higher temperatures 1100deg. F (about 600 deg. C). Low temperature expansion effects occur earlier as the steel is first heated to temperatures below 400 deg. C and long span, expansion effects have yet to be compensated for in the fireproofing insulation codes. This deficiency in high-rise office buildings using large open areas, and long span composite flooring systems is a new finding uncovered by the study of the collapse of the Twin Towers and Buildings 5 and 7 and was first illuminated in the engineering computer studies. Further scientific research is critically needed to determine what changes are needed in fireproofing insulation types and schedules for the longer spans and the possibly of requiring span limitations, redundancies in column strength, connections designed to compensate for the expansion and separate lateral column support.
A key characteristic of large open office areas not compartmented by firewalls is that a fire can release a large quantity of heat as the fire spreads over the floor if not extinguished immediately as by a working, water spray system (sprinkler) or by the Fire Department. The water spray systems in both towers and Building 7 were damaged by the forces of plane impacts and in Building 7 by the tower’s collapse impacts damaging the water mains in the streets which also deprived the Fire Department of water. Fire size is another major factor affecting steel failure. FDNY Chief Vincent Dunn explains:
“A large-area fire in which flames involve much of the steel beam in a short period of time will heat a beam to its critical temperature more quickly. A so-called ‘flash fire’—which suddenly involves a large area with flame, can heat [inadequately fireproofed] steel to its failure temperature rapidly.”4
Because long span, lightweight steel, bar-joist floor construction was used to provide wide-open spaces free of columns within the WTC towers, vulnerabilities were introduced. Since lightweight steel trusses are affected by a large fire faster than heavy members, and since they span such larger areas, their failure would be much more serious than would the failure of a short-span element.
The other thing about long span floors is that when an interior column or columns fail under such large area circumstances the building may not be able to redistribute the floor loads to other columns and the collapse is likely to progress upwards putting all the floors above into suspension. If the building is not protected against progressive collapse, global (total) collapse can ensue. Building 7 collapsed because one key interior column failed after the long span floors failed around it. Because of the long spans the key column was supporting a large area of flooring on every floor. It was discovered by the NIST computer studies that failure of this one column would have brought the entire building down without any fire. Such a lack of column redundancy should be corrected by deigning the building to withstand the removal any single column.
Reports of Controlled Demolition, Molten Steel, Thermite, etc.
Scientists rarely speak of the ‘truth’ until they have spent enough time examining the evidence. Its amazing to me how the Architects and Engineers for 9/11 Truth who apparently have little or no knowledge or expertise in fire protection or building collapse, just dismiss the reports of the top Fire Protection engineering experts in their fields and take some theological professor’s absurd babble as gospel. I suppose if their car’s engine broke down they would call the local preacher. The vaguest possibility is immediately touted as the truth and repeatedly echoed on the internet without any research or fact checking. Four years after the 9/11 attack and without inspecting any of the steel the Architect Richard Gage was listening to some equally uninformed Philosophy Professor, David Ray Griffin and had an epiphany and from then on he ‘knew’ that the buildings “had to be brought down by explosives”. “That’s the only way that you could have all the exterior columns in Building 7 fail within a fraction of a second.” How does he know all the columns failed at the same moment? These lower columns were out of sight of the cameras. The first thing to fail was the floors on the east side then the east interior columns as evidenced by the east penthouse on the roof caving in. Five seconds later the west penthouse caved in indicating widespread core column failure and than the exterior frame started to descend, but the outside frame was strong and there were large belt trusses around the entire building between the 22nd to 24th floors. These belt trusses held the upper building steady until a large number of lower exterior columns had failed. With the failure of most of the interior floors and columns there apparently was an 8 floor section of exterior columns without lateral support. When this 8 story section of columns buckled the building began a 2 second period of free fall acceleration. Building 7 took over 13 seconds to collapse not 6.
NIST computer models show that the building was deconstructed by the heat of the uncontrolled fires expanding the long span steel floors, buckling the beams, disconnecting structural steel, and eventually buckling one key column which started the progressive collapse. The design was so flawed that that because that one column buckled the collapse progressed up to the roof and than across the core to take down the entire interior of the building. I want to hear what the Architects & Engineers for 9/11 truth think about a building within which the failure of one column will start a progressive collapse that brings down the whole building. Now that’s an architectural and engineering problem that needs their attention which will not be forthcoming if they continue to believe the buildings were taken down by supposed explosives. The Architects and Engineers for 9/11 truth’s Richard Gage is going all around the country spreading his pseudoscientific misinformation that explosives were used to bring down these buildings.
The top experts in the field, Shyam Sunder the NIST lead investigator, Gene Corley the American Society of Civil Engineers lead investigator both of whom have years and years of engineering experience believe the buildings were brought down by the fires. Gene Corley who was also the lead investigator in the Oklahoma City disaster, - which was destroyed by explosives, - said there was “no evidence of explosives” at the WTC site. He and Johanthan Barnett another experienced Fire Protection Engineer were on the scene immediately and examining the steel. Dr. Barnett described the devastation caused by the interior collapse of several floors in Building 5 (Yes. Building 5.) from fire when the steel beams pulled out from their connections. These are all recognized experts in their fields and have to get things right in order to maintain their positions. I doubt a person inexperienced in the fire protection field could prove them wrong on anything related to the towers collapse without years of study, but they keep trying. The BBC put on the top building demolition expert Mark Loizeaux who explains how the towers collapse could not have been a controlled demolition and all he gets is blasted by the 9/11 ‘truthers’ for being ‘in-on’ the conspiracy.
Their spokesperson Kevin Ryan knew very little about how floor assemblies are tested by his own company Underwriters Laboratory. He worked in the water testing section of the UL. Mr. Ryan reported that they tested the steel and it withstood 2000 deg for 3 and 4 hours. The UL tests 17 foot floor and wall assemblies not the steel per se. The problem is that the long span composite floors used in the towers were never tested by anyone in their long span configuration of 60 feet. Building 7 also used long span steel “I” beams. What most architects apparently don’t yet know is that lightweight, long span steel trusses and “I” beams can fail at fire temperatures not yet compensated for in the codes. The standard furnace test can only handle 17 foot lengths of flooring and doesn’t test the connections for fire exposure. The furnace standards were set in the 1930s, 40s, and 50s when about 15 to 20 feet was the standard span used in high rises built for the more conservative codes at that time. These older buildings used shorter spans, more robust columns and beams, stronger connections and better fireproofing then now and stood up to fires quite well. If a floor failed the push-out forces of expansion and the pull-in (catenary) forces created by the short spans were easily handled by the strength of the rest of the structure. For this reason the codes allowed floors to have a shorter (3 hour) rating than the columns and girders (4 hours). The 17 foot furnace test, currently still used, is meaningless for the longer spans and connections. The main problem in the Tower flooring was due to the differential elongation (expansion) of the steel parts of the trusses.
NIST’s studies found that the different expansion rates immediately deformed the steel parts, buckled the top chords and struts in the bar joist floors and disconnected the composite bond between the concrete slab and the steel joists. Greater thermal expansion of the bottom chords releases the tension and allows the cool top chord to sag and bow downwards until it acts as a cable in suspension creating pull-in forces on the columns. Buckling of the top chord allows the bottom chord to act as a catenary. The contraction of sagging, long span steel flooring during the cool down faze after the fire dies down puts heavy pull-in loads on the connections. It is now known that Building 7 collapsed from expansion and/or contraction in the floor beams disconnecting enough of the beams and girders to affect column stability. There was a second or two when the perimeter wall came down at free fall acceleration but this in no way indicates demolition was involved. There was so much destruction of the interior structure over many floors that long sections of exterior columns failed at essentially the same time.
Many people interpreted the loud sounds and debris being projected out sideways during the Tower collapses as an indication that explosives were used. Most of these loud sounds, heard during the collapses were heard after the collapses began. In order for an explosion to cause a collapse it would have to occur before the collapse. Some ‘thunder’ sounds were heard in Building 7 before the exterior columns buckled and these were probably from floors collapsing and impacting the floors below. Explosive forces great enough to destroy the columns would be as loud as ten times the decibel level (140 db) of standing next to the speakers at a rock concert. NIST reports such loud sounds were not heard nor recorded in the video tapes.
The undamaged exterior walls can be seen bending and buckling inward in the videos of both WTC Towers long before any sounds or ground vibrations occurred. In Tower 2, the exterior columns in the east wall were photographed bowing inward up to 10 inches, 18 minutes after the plane's impact. That's 38 minutes before the global collapse began. To be technical, you could say that Tower 2's collapse began slowly, with possibly some noise or impact sounds from falling floors, about 38 minutes earlier than the official collapse time.
Sequence of buckling of Tower 2’s East wall columns.
The explosive sounds and expanding dust clouds occurred just after the east wall buckled inward and started the collapse, and not before the buckling, as would have had to have happened with controlled demolition.
When the undamaged south exterior wall of Tower 1 was photographed it was bowing inward up to 55 inches on floors 95 to 101, about six minutes before these columns were seen buckling inward. This bowing and buckling was witnessed and video taped by the Police Aviation Unit.
In the North Tower "thunder" sounds were heard when some floors apparently collapsed on the south side 12 to 14 seconds before the top of the building was seen to tilt southward and begin falling as a unit starting the global collapse. Since each section of floor on the long-span side weighed about 500 tons, I would take these 'supposed explosive' sounds in Tower 1 as evidence of a floor or floors detaching and impacting the floors below on the south side which most probably accelerated south column wall failure. The boom, boom, boom, boom, boom repetitive sounds reported by firefighters as Tower 2 was coming down were most likely caused by the sequential collision of impacting floors after the top of the building began falling. The great quantity of air on each floor being compressed in a fraction of a second by great weight and momentum would propel air, smoke, and any concrete dust and debris outward from the building at great velocity by the bellows effect of the floors coming together so quickly.
Initial Collapse Cause
Much consternation has been expressed because of the fact that NIST only analyzed the events up to the point where the Towers were poised to collapse before runaway collapse began and failed to pursue the remaining collapse. This was largely because once the collapse began the chaotic impacts of the floors, walls and columns colliding could not possibly be analyzed accurately with even the strongest computers. As it was, it was a severe strain on computer capabilities to analyze the mechanism of collapse up to the point of runaway disintegration. By dint of computers running for extended periods of time NIST did analyze almost the complete collapse sequence of building 7.
Bar joist Floors
It is clear from the computer studies that the heat from the fires caused differential expansion of the steel parts in the long span, floor trusses in the towers with the resulting thermal bowing in some floors directly exerting pull-in forces on the exterior columns or this thermal bowing could have detached a floor at the weak, single bolt connections which would have impacted the floor below destroying its composite action by separating the concrete slab from the trusses and inducing strong tensile (suspension) forces in the double weighted floor. In other floors thermal expansion of the floor against the columns compressed the trusses which along with shear forces within the trusses buckled the diagonal compression struts collapsing the trusses themselves which went into suspension (catenary action) and this also assisted pull-in and eventually buckled in the exterior column walls. Differential thermal expansion of the concrete slab and the steel has also been shown by NIST to disconnect the knuckles (knuckles are the steel tops of the bent over bars in the trusses which are imbedded in the concrete) from the concrete slab causing loss of composite behavior in the floors.
All these adverse floor effects were caused by steel expansion which begins immediately as the steel is heated. Bowing and buckling can happen at low temperatures (300 C to 500 C) even before the steel beams would have been weakened excessively from higher temperatures. The longer the beam the further it can expand and since the steel still has its full strength the expansion can break the bolts holding the beam and bow or buckle the beam itself. Thermal contraction caused by cooling of sagging trusses or ‘I’ beams after the fire ‘burns out’ or dies down can cause strong pull-in forces on the exterior columns and core columns due to the contraction of the sagging steel trusses or ‘I’ beams.
Columns
In order for a column to support the loads it has to be plumb and in line with the columns above and below. The fact is, columns have to be axially (in line and centered) aligned to support the weight of the building above. If they get out of alignment by 10 to 20 degrees they buckle and can no longer support the weight. The Tower buildings collapsed because the floors first caved in from restrained thermal expansion and from thermal bowing or delamination of the slab and bar joists composite action affecting floor truss stability. The sagging, 60 foot long, floor trusses gradually pulled-in the 59 columns in one exterior wall in each tower and these column walls eventually buckled removing practically all support on one entire long span side. In Building 7 floor failures from steel expansion and/or contraction disconnecting the floor beams exposed a critical column to loss of lateral restraint over many floors and lateral forces causing the column to buckle and remove support for all the floors above and starting the complete progressive collapse of the building.
In the WTC Towers once the exterior columns buckling spread, along an entire wall removing support on one face, the buckling spread around the towers exterior and into the core and the towers began to tilt. With the entire top of the building tilting all the columns were out of alignment and buckling and the leaning top sections of the tower began to fall straight down. Although the North tower antenna appeared from some northern angles to have began falling straight down it actually first tilted to the south because the south wall buckled first and the cantilevered top building section pulled the core along with the entire top over to the south. This is especially telling as evidence of fire induced collapse since all the damage from the plane impact was on the north side which side should have collapsed first,- if the plane damage was contributory,- and the tower should have leaned over to the north. The South Towers’ top tilted to the east because its east exterior wall buckled first from the pull-in forces of the failing long span flooring trusses on that side. Once the tower’s tops began tilting all the columns across the buildings would be out of alignment and easily buckled.
There have been some engineering analyses about the impacting floors slowing down the collapse so that the time to collapse should have been much longer than 'free fall' times of an object dropped from the towers tops. Once the buildings started to tip over from loss of column support on one side, the tremendous excess eccentric weight began buckling all the columns across the building. Once the tilted tower’s tops began descending the columns hit the floors or the lower columns at eccentric angles which easily detached the floors and buckled the columns. In order for the lower building section to offer any meaningful resistance to the falling building top, the columns would have had to hit each other exactly in line and plumb and this was impossible with the top of the building leaning causing eccentric angles of impact.
Once the Towers top building sections began tilting the columns on the side that originally buckled did not line up at all. These columns would have been hitting the floors and would have easily detached or buckled them. After the east wall buckled in Tower 2, the adjacent perimeter wall columns buckled from overloads and the columns on the opposite, west side of the building acted as a hinge would still be bearing on each other but at an eccentric angle which means they also would have also eventually buckled as the top tilted. These columns along with some of the core columns as they buckled are probably what kicked the bottom of the top building section to the west as reported by NIST. Because of the weight of the accumulating collapsing floors, there was a release of incredible potential energy changing to kinetic energy and building momentum as the accumulating chaotic mass of debris accelerated into the cellars.
The heavy core columns depended on the floors for lateral support once they lost lateral support and experienced ‘pull in’ forces and got out of plumb, there would have been little resistance to their buckling at the weak splices. After the upper part of the buildings began descending, with the incredible weight of the top of the buildings’ gaining momentum, like a heavy wedge or sledge all it had to do was break the welded, and single bolt connections holding the floors to the columns.
This is coupled with the fact that the falling top section’s momentum increases as the square of the number of floors impacted as the floors were detached and added to the weight of the descending top. There would have been little resistance to slow the top section's increasing mass of impacted floors acceleration to the ground. Because this acceleration due to gravity increased the speed and momentum of the collapsing floors and building top, the impacts were increasingly violent as shown on the seismic graphs; increasing in amplitude until maximum when the mass of accumulating impacted floors hit bedrock seven stories into the cellar.
Since the Tower's outer wall columns, especially in Tower 1, pealed out like a banana after the building top began to impact and disconnect the floors, these wall columns may have been able to break the connections to the floors ahead of the floors being impacted? In other words, with the weight of the wall columns pealing outward from the vertical along with the added horizontal forces of impacting floors projecting smoke and debris outwards onto these columns, these columns, while leaning out, might have been able to break the wall-to-floor connections ahead of the level of impacting floors or with the excess strain the connections could have failed sooner. If this is possible than I believe that the connection failures could have traveled down the sides of the buildings and accelerated faster than free fall. This might explain the rapidity of the collapses especially in Tower 1. The wall-to-floor connection failures could have traveled down the building sides and in effect started the floors falling before they were impacted by the accumulating mass of impacted floors above. Anyway this mechanism would have surly reduced the failure times of the floor connections.
But these buildings did not collapse faster than free fall times and this is proved by the photos themselves. It can be seen that the detached exterior walls which were falling at free fall acceleration after they detached, were falling faster than the remaining center portions of the buildings. This fact proves the Towers fell slower than free fall acceleration.
The heavy exterior wall columns in the 1500 foot high buildings while pealing off could project the column sections outwards a great distance. This distance (300 to 400 feet) was proposed as only being made possible by explosive forces. I disagree. If a wall is strong enough and doesn’t break up as it falls outward it can fall out flat to a distance equal to its height. The Tower walls, however, did break at the weak column splices as they fell.
The compression of the 12 foot chunk of air on each floor down to a fraction of an inch in a fraction of a second as the floors came together would propel the air smoke and dust outward from the building at great velocity. The lightweight aluminum cladding as it broke free from the buckling columns also would have been propelled outward a great distance by this expanding cloud of air, smoke and dust. This gas compression would account for huge dust clouds and pieces of aluminum seen projected outwards from the upper sections of the collapsing buildings.
The light reflected off the aluminum pieces at the north wall of Tower 2 were interpreted as flashes from explosive 'squibs'. These pieces of aluminum broke off from buckling columns. The flashes below the buckling east wall may have been from the aluminum cladding breaking free from the lower columns as they expanded after being unloaded of axial compressive weight by the buckling of the wall above and their expansion breaking the connections to the cladding. Also explosives leave characteristic tears and fractures in steel and especially in aluminum, and such indications were not found anywhere in the debris pile.
The compression of air in the elevator and air-conditioning shafts by the collapsing upper building section and floors, would project air, smoke, and dust down these shafts and out any path of least resistance on any floor or any of the HVAC air intake or discharge openings on the lower mechanical equipment floors in the exterior walls. This accounts for the plumes of smoke seen projecting outwards sideways from the buildings well below the collapsing floors. There were quite extensive Heating, Ventilating, and Air Conditioning (HVAC) shafts built into the building. These vertical shafts are connected to air conditioning exhaust and intake ducts open to the exterior on the mechanical floors.
Deep Seated Pockets of Fire
After any fire in which a building collapses, there often remain pockets of fire deep within the rubble pile. These ‘deep seated pockets of fire’ sometimes cannot be reached by water streams because of their being covered by debris. Air is sometimes drawn up from the bottom of the pile and feeds these inaccessible fires with air because these natural convection currents. Heated air rises because of its expansion and resultant buoyancy and is replaced by cool air drawn in from the bottom and sides of the fire. This air flow can become rapid because of the high temperatures developed. The more air drawn in the hotter the fire becomes and the increased temperature increases the convection currents which draw in more air. After a collapse there is more combustible material available to feed the fire. Like in a furnace the containment of heat by insulation provided by the compacted combustible material surrounding the fire allows the gradual increase of temperature. I am convinced that temperatures of over 2000 deg F. can easily be developed in these deep seated pockets of fire in the rubble of a collapsed building. This temperature is still incapable of melting steel unless there is excess oxygen available.
These fires can last for days and the heat can become intense and can heat any steel in proximity to the fire until the steel is glowing red, orange or yellow hot. These pockets of fire are common at burning building collapses and in no way evidence that that explosives or thermite were used to demolish the buildings. These underground fires are similar to blacksmith forge fires where air is blown into the charcoals by a bellows to raise the temperature of the fire to heat a piece of steel or iron. The blacksmith can tell how hot the steel or iron is by its color and can tell when the steel is soft enough to work it with a hammer.
I talked to a blacksmith at Old Bethpage Restoration on Long Island and he told me that he can create enough heat to burn and melt the steel and it sometimes happens when he is talking to people and absent mindedly keeps pulling the bellows chord and feeding air into the coals. Burning the iron melts the steel and ruins the work.
"With bellows blowing additional air through the fire, it can reach temperatures of about 3,000° Fahrenheit. Iron burns at 2,800°, however, so the smith has to be careful to not ruin his work! … The smith's fire contains too much oxygen to allow iron to melt; as it approaches its melting point the iron burns instead."
http://www.osv.org/cgi-bin/CreatePDF.php?/tour/index.php?L=12&PDF=Y
Pure oxygen is used in oxyacetylene torches to actually ignite burn and melt the steel when cutting. These torches were used to help clear the debris pile during search and recovery operations. A slag of melted and re-solidified steel and Ferrous oxide is formed on the opposite side of the cut. This slag formation and the angle of these cuts were erroneously reported to be evidence of cutter (demolition) charges having been used to sever the columns. Small molten pieces of glowing steel cool into spheres as they fly out from the cut. These steel microspheres,- said to be evidence of thermite,- would also have been produced during the buildings’ construction by welders and retained in the concrete or else where only to be released during the collapse.
The deep seated pockets of fire often have to be dug out by hand tools, back hoes or grapplers in order to expose the burning material for extinguishment. It is common to hold off hitting the fire with water until it is fully exposed in order to prevent the great amount of steam that would be created from obscuring the work area until the fire is fully exposed and can be quickly extinguished. This is what is happening in the picture of a grappler pulling out a piece of glowing hot steel from the debris pile so often described as ‘molten’ steel.
About the “meteorite” recovered from ground zero. Everyone uses the word ‘molten’ in describing the steel in the meteorite when it actually is deformed pieces of the bar joist flooring compacted with concrete and pieces of furnishings. This is careless language. Apparently people seeing steel deformed by heat immediately call it molten or melted steel. Melted or molten steel indicates a liquid state which only occurs at higher temperatures than an ordinary fire can produce. The meteorite is a piece of pancaked concrete and steel floors fused together by high impacts. It contains charred pieces of books and paper which would not be present if heat high enough to melt steel existed at anytime in the “meteorite”.
Much has been made of the presence of molten metal in the debris pile after the collapse. Presumably this molten metal was somehow thought to be connected to explosions or thermite charges, but there were Uninterrupted Power Supply (UPS) battery rooms on some floors of the Towers and Building 7. These battery rooms supplied continuous battery power to computers if the electricity failed for any reason. These batteries contained tons of lead which melts at low temperatures [327 C (621 F)]. The heat from the fires in the debris pile could easily have melted this lead and the aluminum from the plane and aluminum from the tower’s own cladding which were probably the metals that were seen flowing through the pile. NIST reported UPS in the 13th floor of Building 7 and the 81st floor of Tower 2. There were also quantities of lead, tin, silver and even gold used in the computer circuit boards. In the some people’s imagination the reported ‘flowing molten metal’ became ‘rivers of molten steel’.
Additionally the EPA reported over 400 different chemicals in the dust and debris. These chemicals could easily be assembled conceptually to propose any type of chemical reaction imaginable including thermite reactions. In addition thermite reactions are rapid they are over in a matter of seconds and wouldn't last the hours or days at which times the molten metal was observed. As far as I know thermite has never been used to demolish buildings and the expertise probably doesn’t exist. Thermite is hard to control and can’t be held against the columns because it would burn, spall or melt down through any material used to support it against the columns long enough to do enough damage to cause the column to buckle.
About the concrete pulverization into dust reported to be only possible by explosive charges; F.R. Greening did a paper called Energy Transfer in the WTC Collapse in which he says "the energy required to crush concrete to 100 μm particles is 1.9 × 1011 J, which is well within the crushing capacity of the available energy. Hence it is theoretically possible for the WTC collapse events to have crushed more than 90 % of the floor concrete to particles well within the observed particle size range." http://nistreview.org/WTC-REPORT-GREENING.pdf. I would also investigate the possibility that the concrete was sub par to begin with due too much air or water having been added during the pouring and finishing operation to speed working and leveling the cement or to freezing during curing in the course of construction.
Do you think the architect or engineers who built the Towers would want to admit the deficiencies in design, fireproofing and other construction weaknesses after their buildings collapsed? Do you think they will get any other jobs after 4 of their buildings collapsed from fire? How come the 9/11, Architects & Engineers for truth never mention Building 5. Building 5 had a serious fire on many floors and had several floors collapse from the steel beams being disconnected from the columns due to thermal expansion, sagging and catinary action tearing out the bolted beam connections? (ASCE, Building Performance Study) I suppose that some of the ‘truthers’ never even read the American Society of Civil Engineer’s or the NIST’s report. Did building 5 also have charges set beforehand? How many other buildings had hypothetical charges set beforehand and were never set off? If they went to all the trouble to rig all these buildings with alleged explosives, why didn’t they just set them off and forget the planes and the fires. Waiting for the planes and fires would surely increase their chances of being detected.
There are so many questions answered by the fire theories and so many unanswerable questions posed by the demolition theories that it is ludicrous to continue the proposition that explosives had to be employed to collapse these buildings.
Do you know that the Port Authority of NY, NJ didn't legally have to follow any building codes? The reason the columns broke at the splices was that they had serious weaknesses due to lack of reinforcing plates or even welds on most of the exterior column, bolted splices and not because of the ridiculous idea repeated incessantly by Richard Gauge that they were broken up into short pieces, presumably by explosives, ‘so they would fit onto the trucks to be carried away’. The long span truss floors were never tested for fire resistance at their design length. Why do you think it took so long to get the plans for the buildings after they collapsed while the building engineers had them all along? I am sad to think the architects and engineers for 9/11 truth would be accepting of such a convenient excuse,- that explosives or thermite was involved,- but that idea would allow them to avoid the introspection necessary to fully realize their own ignorance of what fire can do to steel beams and columns,- a necessary realization before meaningful knowledge can be developed to make their buildings safe.
About the eye witnesses hearing supposed explosions; there are many reasons that loud sounds can be produced at a fire. Most of the people in Tower 2 did not know Tower 1 had been struck by a plane but they heard the explosion and even felt the radiant heat produced by the fireball. Often at fires the ones closest to the fires and engaged in heavy work have a very limited overall conception of what is actually happening. When you don’t know what’s happening especially in the dark smoky conditions your imagination starts to work. Barry Jennings said he was stepping over dead bodies when being led out of building 7 after it was hit by pieces of Tower 1. He later admitted that he never actually saw these bodies. He must have imagined it. I suppose he also imagined seeing the two Towers still standing amid the smoke after he experienced a supposed explosion while descending the stairway. The “explosion” that Barry Jenning’s heard was probably the pieces of Tower 1 hitting Building 7. Even experienced reporters couldn’t believe the towers were gone from the skyline after they collapsed.
When Tower 2 collapsed most of the people in Tower 1 thought the sounds and vibrations came from the building they were in and they even felt a rush of air up the stairs as the air was compressed in the cellars. The fact that they are in strange circumstances with lack of information, smoke and possibly darkness, and the presence of strange sounds creates a fertile field for the imagination. There can also be real smoke explosions (backdrafts) particularly in fires that have a flammable liquid involved. One elevator shaft that extended into the cellars experienced a fuel-air explosion from the jet fuel spilling down and evaporating in the shaft. There were other fuel-air explosions in the elevator shafts. There could have been floor detachments impacting the floors below and producing loud sounds before any general collapse began. Explosives produce loud distinctive pressure waves that can leave people deaf or blow out eardrums and usually blow out all the windows on the particular floor and in any buildings nearby. This kind of sharp piercing crack was not heard. The windows broken out and marble wall panels detached on the interior of the first floor lobby were probably because of torque or bending forces experienced on the lower floor columns from the plane impacts many floors above. The buildings were reported to sway several feet when the planes hit the towers. In order to let additional light into the lobby these lower exterior columns were fewer and further apart than the columns above. The lower ‘core’ columns in this area were stronger and securely cross braced to compensate for this weakness of the exterior columns in the lobby. This fact was probably responsible for saving the lives of the members of a Ladder Company who were trapped in the stairwell on these lower floors during the collapse. It’s too bad this strength wasn’t continued up the core to the building top. It may have saved many more lives by protecting the stairways. The reports of "explosions" in the cellars were also probably from such column or floor displacements or from jet fuel ignitions in the elevator shafts. If you imbed a stick into the ground and hit it with another stick most of the deformation will be in the ground around the bottom of the stick. There were reports of split walls and ceiling collapses on many floors after the planes hit.
The “mysterious” collapse of Building 7.
How do you think that the alleged conspirators knew that Building 7 would be hit by pieces of Tower 1 which would set it on fire? They would have to know this beforehand in order to set the mysterious explosive charges that allegedly demolished the building. Why did they wait 5 hours while the fires burned before they set off these alleged charges, and how did these so called explosive charges or thermite withstand the fires for 5 hours without igniting and burning off? The NIST computer models show steel beams buckling, sagging floors and disconnection of the beams from the columns and finally failure of one key column which started the global collapse, all from the heat of the fires expanding the long span steel and breaking the bolted shear connections in Building 7.
BBC reporting error on Building 7 collapse.
You may ask “How did the BBC know that the Towers were going to collapse?” The BBC didn't know. Did you ever hear a mistake made by a reporter? Or do you believe everything you are told by a TV reporter in the heat of an emergency? The BBC reporter on the air received an erroneous report that the Building 7 had collapsed before it actually did and reported it well before the actual occurrence. It was a simple mistake.
I can imagine how it happened. In addition to the damage done to Building 7 by the heavy steel column trees that pealed off of the collapsing towers some of these steel columns penetrated the roads and broke the nearby water mains. There was fire on many floors in Building 7 and without water these fires could not be controlled. The collapse possibility was anticipated by the Fire Dept. who ordered the evacuation out of the building and out of a “collapse zone” about 600 feet around the building. Apparently they were the only people who realized the possibility that an out of control fire on multiple floors in a steel framed, long span, open area, office building could cause a collapse. They had just experienced the collapse of two similar buildings trapping and killing many of their brothers. The ‘collapse zone’ was a large area including buildings and streets around Building 7 and clearing this large area of people was a big problem. To get some people reluctant to move swiftly out of the area I can imagine someone saying “the building’s coming down”. A reporter may have heard this and called his boss and told him the building 7 is coming down. The person receiving the call believed the building was already collapsing. It went out over the air as the building had already collapsed before the actual occurrence. The anticipation of collapse was a brilliant call by the Fire Dept. and no lives were lost when the 47 story building collapsed a few hours after the evacuation order was given.
This is a message from Chief of Department (ret.) Daniel Nigro the chief in charge of the fire, addressing the conspiracy theories surrounding the collapse of WTC 7.
Release date: September 23, 2007
Regarding WTC 7: The long-awaited US Government NIST (National Institute of Standards and Technology) report on the collapse of WTC 7 is due to be published at the end of this year (although it has been delayed already a few times [ adding fuel to the conspiracy theorists fires!]). That report should explain the cause and mechanics of the collapse in great detail. Early on the afternoon of September 11th 2001, following the collapse of WTC 1 & 2, I feared a collapse of WTC 7 (as did many on my staff).
The reasons are as follows:
1 - Although prior to that day high-rise structures had never collapsed, the collapse of WTC 1 & 2 showed that certain high-rise structures subjected to damage from impact and from fire will collapse.
2. The collapse of WTC 1 damaged portions of the lower floors of WTC 7.
3. WTC 7, we knew, was built on a small number of large columns providing an open Atrium on the lower levels.
4. Numerous fires on many floors of WTC 7 burned without sufficient water supply to attack them.
For these reasons I made the decision (without consulting the owner [Larry Silverstein], the mayor or anyone else - as ranking fire officer, that decision was my responsibility) to clear a collapse zone surrounding the building and to stop all activity within that zone. Approximately three hours after that order was given, WTC 7 collapsed.
Conspiracy theories abound and I believe firmly that all of them are without merit.
Regards, Dan Nigro
Chief of Department FDNY (retired)
On October 4 2001 Chief Nigro said; “The most important operational decision to be made that afternoon was the collapse [of Tower 1] had damaged 7 World Trade Center, which is about a 50 story building, at Vesey between West Broadway and Washington Street. It had a very heavy fire on many floors and I ordered the evacuation of an area sufficient around [building 7] to protect our members, so we had to give up some rescue operations which were going on at the time [under the ruble of Tower 1] and back the people away far enough so that if 7 World Trade Center did collapse, we wouldn’t lose any more people. We continued to operate on what we could from that distance and approximately an hour and a half after that order [to evacuate the building and collapse zone] was given, at 5;30 in the afternoon, 7 World Trade Center collapsed completely. I continued to operate at the scene until probably somewhere around 8 o’clock, at which time I borrowed Chief Meyer’s car, because mine was destroyed and went home to [take a], shower, change my clothes and I came back to work at approximately between 11 and midnight with Chief Turi.”
(New York Times interview Date; October 24, 2001 , transcribed by Elizabeth F. Nason)
If you really believe that all the top fire protection engineers from the American Society of Civil Engineers (ASCE) and government scientists from National Institute of Standards and Technology (NIST) investigating the collapse are in on a conspiracy and also want to accuse the BBC, the NYC Fire Department, the NYC Police Department, the Red Cross and all the Government agencies controlling access Building 7 of being ‘in on’ a secret controlled demolition even though there was no hard evidence than I would say you may be suffering from a case of paranoia. Paranoia can easily become contagious when people panic and no longer trust their government. We certainly had reason not to trust our previous government. I would say that if you really believe these preposterous demolition theories you should do some soul searching and possibly seek some therapeutic help.
In conclusion I think all the reports of controlled demolition can be explained by sounds or sights produced by the plane impacts and jet fuel and air explosions; the sounds of the Towers collapse. When the interior of building 7 collapsed it would have produced loud sounds well before the exterior walls began collapsing.
It’s an ill wind that blows no good and the good thing is that NIST now has an effective computer model to test whether a new or existing building is safe from collapse from fire. The architects and engineers should use this capability to assure any proposed or existing designs are safe. Another good thing is that any corrections proposed can be run through the computer and any tested for effectiveness. This NIST computer work,- which modeled the fires and every steel column and beam with their connections,- shows that Building 7 was deconstructed by the heat of the uncontrolled fires expanding the long span steel floors, buckling beams, disconnecting structural steel connections, collapsing the floors and eventually buckling one key column which started the progressive collapse. The connections and lateral support were so week that that the collapse of one key column progressed across the core to take down the entire interior of the building. Now that’s an architectural and engineering problem. I want to hear what the Architects & Engineers for 9/11 truth think about a building that can loose one column which starts a progressive collapse that brings down the whole building. Design problem? They should be eager to get those computer models working instead of raving about some imaginary explosives having brought down these buildings.
Arthur Scheuerman
Retired Battalion Chief, FDNY
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