| Pentagon C Ring Exit Hole Mystery
Article by Michael Meyer, Mechanical Engineer, June 10, 2006
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[Original article at 'Scholars for 9/11 truth']
A great deal has been written about the damage to the Pentagon on 9/11. The focus of this discussion is on the mysterious, and officially unexplained, "C-Ring Exit Hole". The C-ring exit hole is significant because it is not consistent with building damage from a Boeing 757 impact. The C-Ring exit hole carries a unique signature, which can only be explained by something other than a 757 impact. No explanation is offered for this hole in the Pentagon Building Performance Report (2.4 Mb PDF) or the official 9-11 Commission Report.
The exterior C-ring wall is the last wall (the third wall traveling into the Pentagon) that sustained significant damage during the Pentagon attack. On 9/11, a near perfectly round, nine foot diameter hole was cut in the C-Ring wall, known as the "C-Ring exit hole". It is approximately 310 feet (95 m) from the impact on the outer Pentagon wall (E-ring). The unique features of this hole include: its circular shape, the clean cut hole in the wall with no visible damage to the wall immediately surrounding the hole, and steel rebar is cut by the forces which created the hole. For an overview of the hole, see this page.
Below: the exit hole (p. 30) and a diagram showing the location of the exit hole in relation to the plane impact (p. 36) - click to enlarge. Both images are taken from the Pentagon Building Performance Report, January 2003.
From the impact on the E-ring wall, to the C-ring Exit hole, is an open office space with only support columns and ordinary construction interior walls. According to the Building Performance Report, there were intact (but damaged) support columns starting at roughly 160 feet (49 m) into the building in the aircraft flight path, indicating that the fuselage of the aircraft had effectively been destroyed by this point. The C-ring wall was constructed of steel mesh and rebar reinforced brick, 8 inches (20 cm) thick. Details are shown here.
| Nose cone theory
The initial explanation offered was that nose cone/fuselage of the 757 aircraft punched all the way from the E-ring wall, to the C-ring wall, to create this exit hole, the "nose cone" theory.
The structural design of the 757 is based on the structural loads of a pressurized vessel (the cabin), and the structural and aerodynamic loads from the wings, control surfaces, and the fuel. The plane is made as light as possible, and not made to handle impact loads of any kind.
This "nose cone" theory was quickly discounted as there was no significant aircraft wreckage found at the C-ring wall, nor would an aircraft impact have cut a clean hole without disturbing any of the surrounding wall. There were also support columns still standing in the flight path of the aircraft.
"At a depth of approximately 160 ft (50 m) into the building, columns 3G, 3H, 3J, and 5J were damaged but still standing, although in the direct path of the fuselage. With a maximum spacing of less than 14 ft (4 m) between pairs of these columns in a projection perpendicular to the path of the fuselage, it is highly unlikely that any significant portion of the fuselage could have retained structural integrity at this point in its travel. More likely, the fuselage was destroyed much earlier in its movement through the building. Therefore, the aircraft frame most certainly was destroyed before it had traveled a distance that approximately equaled the length of the aircraft."
| 'Circle of energy' theory
Next, investigators from Purdue University proposed that fuel, airplane material, and momentum from the aircraft created this circular cut out by continuing into the building after the plane had been destroyed. This "circle of energy" concept seems improbable for a number of reasons:
1. The airplane materials included the plane and fuel in the fuselage and wings. This material would have been spread out over a non circular area which included the wings and fuselage.
2. There does not seem to be any historical precedent for this phenomenon to have occurred.
3. There were support columns that remained standing in the path between the impact point and the C-Ring exit hole that would have deflected parts of this "circle of energy".
4. The impact of this material would have knocked the wall down, or caved it in due to the mesh and rebar reinforcement, not created a clean cut hole.
To have this material and energy "form up" into a circle so as to cause this hole seems extremely unlikely. This "circle of energy" theory seems to have also been discounted.
| 'Shock wave' theory
The National Geographic Channel aired a program "Seconds to Disaster" which depicted the events at the Pentagon on 9/11. This program aired most recently on May 24th 2006. They offered the following explanation for the C-Ring exit hole: secondary explosions from the impact and jet fuel, coupled with the geometry of the inside of the impacted Pentagon, allowed shock waves to cause this circular hole.
This "shock wave" concept also seems improbable for a number of reasons:
1. The interior section of the Pentagon where the 757 impacted was roughly 200 feet (60 m) wide and deep with a significant hole from the 757 impact. Air is a compressible gas, and the forces required to knock down a mesh and rebar reinforced wall are substantial. Shock waves could certainly be present, but these shock waves would be in air, and would be spread throughout the interior section of the Pentagon. The hole in the C-Ring would require extremely localized forces; to have these shock waves form a clean cut circular hole, including cutting rebar, is extraordinarily remote.
2. Any forces impacting the wall from shock waves would be spread over some area of the wall. These forces would knock the wall down or crumple it if they were strong enough. These shock waves would also be influenced and deflected by the support columns. Once again, the clean cut hole defies the explanation of shock waves.
3. There does not seem to be any historical precedent for this to occur, as there are routinely secondary explosions during fires, but this clean cut circle phenomena has not been reported elsewhere.
Note: I asked to be put in contact with the authors of the "shock wave" theory, but the National Geographic Channel merely directed me to the Pentagon Building Performance Report and to Pentagon reconstruction website as sources for the program. Neither of these documents offers any explanation for the C-ring exit hole.
| Shaped charge?
So what other possibilities could there be for a hole which has these unique characteristics. I have previous experience with shape charge warheads, and anyone with this experience would immediately recognize the hole to match that caused by a shaped charge warhead or device.
The C-ring exit hole has these distinct features, which would have occurred if this wall was struck by some sort of shaped charge:
1. The hole is circular as the typical shaped charge warhead is round.
2. The hole is cleanly cut, in that the walls surrounding the hole do not appear to have suffered any visible forces as would be expected from the extremely localized and focused energy from the shaped charge warhead.
3. Windows are broken outside of the C-ring exit hole. Shock waves from the shaped charge high explosive are strong enough to break typical glass (but not a reinforced brick wall).
4. The wall beyond the C-ring (towards the interior of the Pentagon) is relatively undamaged, only some light charring. The force of the shaped charge warhead is extremely localized and focused and would have dissipated shortly after it breached the C-Ring wall.
What is a shape charge? In simple terms it is high explosives formed in a very specific geometry so that the explosive force is extremely focused. Some good general information can be found at wikipedia. Look at the hole in reinforced concrete (left) made by a TOW bunker buster. You can see how the wall is undamaged except for the hole; also note how the rebar is cut.
Beyond the similarities in the hole shown in this brochure, are there any other details about the Pentagon that raise more questions about the hole in the C-ring wall. On Russell Pickering's web site, www.pentagonresearch.com, he has identified mistakes in the classification of damage to the Pentagon near the C-Ring exit hole. In summary, the Pentagon Building Performance Report indicates gradual decreasing support column damage as you travel into the pentagon along the flight path, to where there is limited damage by the C-Ring exit hole, but this is incorrect. The column damage increases again near the C-Ring Exit hole. This would be consistent with a shape charge warhead detonating near or at the C-Ring exit hole. See the detailed write up here.
Was the Pentagon Building Performance Report team allowed uncontrolled access to the site? Not even close, access was limited and they were escorted, see excerpts from the Pentagon Building Performance Report here. Note that the Building Performance Report team was not allowed to see this exit hole. The FBI provided a photo and description. Why would this team not be allowed uncontrolled access to assess building damage? It should be noted that this team never saw any damage to the Pentagon until all of the wreckage and debris were removed.
So how did a shaped charged warhead get this far into the Pentagon? One possible explanation is a multi stage shaped charge warhead device. I do not propose that the following device was used at the Pentagon, but one such multi stage device is described here. A page or so into this site describes a weapon called a PAM, or "Penetration Augmented Munition":
"Although compact and lightweight (approximately 35 pounds, 33 inches long), it contains the power of four explosive charges and when deployed, can effectively destroy bridges, runways, roads, and tunnels".
It describes a technology where multiple shaped charges are used together, where the first charge creates a hole for a second, and so forth. The successive charges can be set off by separate sensors which detect the impact with a wall. If you were to design a "bunker buster" warhead where you had to penetrate multiple reinforced walls, this would be technology to utilize, to allow you to penetrate further into a multi walled structure than with a single shape charge warhead alone. Due to the lack of walls between the exterior E-ring wall and the C ring wall, it is likely that such a device would travel until it hit a support column. Hitting a support column at an angle could serve to deflect slightly the trajectory of the device. Following this theory, the last charge struck the C-ring wall and created the C-Ring exit hole. Having the device follow a deflect path would also explain how there were still support columns in the direct path of the aircraft to the C-Ring exit hole.
If something smaller than a 757 hit the Pentagon, a multi stage shape charge may have been part of the payload to increase the damage into the building, to better approximate the damage that would be envisioned by a larger 757. A shaped charge warhead would seem to be the only explanation that fits the evidence of a sudden increase in damage to the Pentagon near the C-Ring exit hole and the C-ring exit hole itself.
... "The first time I saw the C-Ring exit hole, a chill went down my spine because I knew that the only way to cut a clean hole in a reinforced brick wall (including cutting through rebar) is with a shaped charge warhead. With any type impact or wave, forces would have caused the wall to crumble or cave in, without cutting through rebar."...
The only explanations offered by the "official" community, the "circle of energy" and the "shock wave theory", have no precedent, and violate some basic common sense and physics. My proposal fits the classic shape charge damage seen from a typical shaped charge warhead. The first time I saw the C-Ring exit hole, a chill went down my spine because I knew that the only way to cut a clean hole in a reinforced brick wall (including cutting through rebar) is with a shaped charge warhead. With any type impact or wave, forces would have caused the wall to crumble or cave in, without cutting through rebar.
Many people have claimed that there is no evidence to doubt the official version of events on 9/11. I guess that really depends on your definition of evidence. With the C-Ring exit hole, we have a hole that is clearly out of place with a 757 impact, we have investigators that are not permitted to see the hole, and we have damage near the hole not accurately presented in an official report. What is your threshold for simply accepting a story from the government?
The C-ring Exit hole is but one small chapter in the unexplained events of 9/11. There are many other similar, unexplained events. Doesn't the fact that our Republic was forever altered by the events on 9/11 require an investigation that puts to rest all of these questions, no matter where it leads?
For the sake of completeness, we (at 911truth.dk) should add that Popular Mechanics claims that the hole was made by the plane's landing gear.
The tidy hole in Ring C was 12 ft. wide--not 16 ft. ASCE concludes it was made by the jet's landing gear, not by the fuselage.
This is all that the American Society of Civil Engineers (ACSE) had to say about the landing gear in their Pentagon Building Performance Report (2.4 Mb PDF), p. 40:
The front landing gear (a relatively solid and heavy object) and the flight data recorder (which had been located near the rear of the aircraft) were also found nearly 300 ft (91 m) into the structure.
Aside from presenting a picture of the 'exit hole' and marking its position on the diagrams, the ACSE says nothing about it, and certainly doesn't say it was caused by the landing gear.
Above: close up shot of the top left side of the hole. Note that the damage is completely consistent with the detonation of a shaped charge on the inside of the building. The explosive jet appears to have formed a wide, shallow cone. This would explain why the outer layer of bricks have been punched out in a larger diameter circle.
As an alternative to Meyer's multi-stage missile warhead theory (outlined above), a shaped charge, such as a 'Rapid Wall Breaching Kit', may have simply been affixed to the inside wall and detonated manually.