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For those who still question what Larry Silverstein meant when he said "pull it" when talking about the collapse of the WTC 7, Jeff from PumpItOut.com called demolition experts Controlled Demolition, Inc (CDI) and asked them what "pull it" means in demolition terms. This is what CDI told him:
Click here to listen to conversation
Female receptionist: Good afternoon, Loizeaux Company.
Jeff: Um, sorry, do I -- is this Controlled Demolitions?
CDI: Yes it is.
Jeff: Ok, I was wondering if there was someone I could talk to briefly -- just ask a question I had?
CDI: Well what kind of question?
Jeff: Well I just wanted to know what a term meant in demolition terms.
CDI: Ok, what type of term?
Jeff: Well, if you were in the demolition business and you said the, the term "pull it," I was wondering what exactly that would mean?
CDI: "Pull it"?
Jeff: Yeah.
CDI: Hmm? Hold on a minute.
Jeff: Thank you.
CDI: Sir?
Jeff: Yes?
CDI: "Pull it" is when they actually pull it down.
Jeff: Oh, well thank you very much for your time.
CDI: Ok.
Jeff: Bye.
CDI: Bye.
Many buildings have their steel frames encased in concrete, which was not the case with the WTC Towers, whose fire protections were dislodged by the aircraft impacts.
Wrong, the WTC were encased in concrete read about the so call bathtub under the WTC.
FIREPROOFING" AT THE WTC TOWERS
APPLICATION DEFICIENCIES
Fireproofing was applied directly to the long joists that supported each of the floors. Inspections of the floors with asbestos-containing fireproofing (up to the 38th floor in the North Tower) found that there were numerous areas where the fireproofing had never been applied. Top and bottom chords and truss web members were exposed, and the red lead on the trusses was clearly visible in many locations. Photo 1 shows a truss with fireproofing missing from its end where it meets the outside wall. Also, the fireproofing was frequently thinner than the 3/4 inch described in the Federal Emergency Management Agency-funded ASCE BPAT report on the collapse of the towers. Many of the problems observed were clearly the result of poor workmanship.
However, the nature of the structures that were fireproofed and application methods used could also contribute to the problem. Applying fireproofing to a long-span or any type of joist construction is difficult. The round rods and small angles making up a truss are difficult targets for the installer. Spray fireproofing materials are typically applied from the floor with an extended spray nozzle. The installer may be unable to reach or see certain areas of the trusses that must be covered. This frequently results in thin or absent fireproofing on surfaces hidden from the floor by the bottom of steel members (photo 2). In the WTC, this resulted in sections of the top surface of the bottom chord of the trusses receiving an inadequate coat of fireproofing. These are deficiencies that would have been easily discovered by the ASTM field quality assurance tests for adhesion, cohesion, thickness, and density had these test methods existed at the time of construction.
LACK OF QUALITY ASSURANCE TESTING
The WTC was built before there were accepted standards for determining if the fireproofing as applied in the field would perform properly. Would the material remain on the steel (adhesion), resist physical damage (cohesion), insulate properly (thickness and density), and behave as a fire retardant? Architects relied on the "testing" undertaken by Underwriters Laboratories. However, without field quality assurance tests, there was no way of knowing if the properties of the applied fireproofing matched those of the material subjected to the UL test. The previously discussed tests would not become available until years after the completion of the WTC. For example, the ASTM test for adhesion would have detected the bonding defects of the fireproofing on core columns. This test and the ASTM test for thickness and density would have determined the adequacy of the spray fireproofing on the floor joists.
The WTC should not be considered unique in this regard. The fireproofing in any building constructed before the ASTM standards became available in 1977 should be considered suspect.
Photo 1: WTC Steel Structure Inspection
Photo 2: WTC Steel Structure Inspection
ACCUMULATED DAMAGE TO FIREPROOFING
There is another important aspect to this issue. There is no existing requirement in any building or occupancy code to inspect the fireproofing in a building periodically to determine if it has degraded through gradual physical damage. This is even true for new construction where the fireproofing is installed and tested early in the construction process. Successive work by many trades often damages and removes whole sections of fireproofing. In the WTC, the fireproofing coatings had been damaged by later construction and renovation in many locations.
LESSONS LEARNED
In considering the possible causes of the collapse of the WTC towers, the possibility that the initial application of fire-resistive coatings was deficient must be considered. The implications of this are far ranging. The fire safety of buildings depends on the fire-resistance ratings' successfully resulting in buildings that stay standing despite fire damage. Prior to the collapse of the WTC towers, it was thought that adherence to the fire-resistance ratings in the building codes would result in buildings that were safe for occupants and for those who fight fires. However, the entire scheme currently used to make these determinations must be called into question. If the WTC towers were properly protected but fell anyway, then this would indicate that the fire-resistance ratings and structural reliability of buildings as they are now built are insufficiently protective. However, if the buildings failed because the fireproofing was improperly applied, then the standards for fireproofing application and maintenance need to be strengthened. Peoples' lives depend on properly analyzing these issues and then taking appropriate corrective action.
Deficient firestopping
Deficient firestopping provides an avenue for fire spread. Columns, girders and beams are commonly protected with spray asbestos insulation or a composition material. Spray insulation has been tested to offer four-hour test ratings on columns, three hours on beams and girders.
Test conditions, however, do not match actual conditions in the field. Insulation adhesion may be ineffective because of rust. Frequently, insulation is applied to rusted metal that has not been properly treated before application; the insulation's consistency may vary; its application may be inconsistent; or it may be dislodged during original and new construction and maintenance.
www.fireengin...wtc-towers.html...
14 years on, what are your views on one of the most important events in modern history?
Wrong, the WTC were encased in concrete read about the so call bathtub under the WTC.
That being said, I still struggle to wrap my mind around WTC7's seemingly perfect collapse.