DisasterEditOn 18 May 2009, approximately 2,000 people had gathered in the atrium to participate in and watch a dance contest. At 7:05pm local time (21:35 UTC), the walkways on the second, third and fourth floors were packed with visitors as they watched over the active lobby, which was also full of people. The fourth floor walkway was suspended directly over the second floor walkway, with the third floor walkway set off to the side several meters away from the other two. At 7:12pm, the fourth floor walkway collapsed onto the second floor walkway, then both crashed into the lobby below. As many as 100 people were killed in the initial collapse. The walkways' collapsing rendered the lobby's two main entrances inaccessible, leaving spectators with only a hallway leading to a single-door exit to a smoking patio as their means of escape. As the walkways collapsed, a panic ensued, and hundreds of people rushed toward the narrow corridor causing a bottleneck at the hallway's entrance. A huge crush formed at the exit to the smoking patio, since the door opened inward toward the corridor. People were being pressed up against the door, thereby unable to open it, by the weight of the crowd behind them. People were packed in so tightly in the corridor that many died standing up of compressive asphyxia. The hallway quickly started to fill with people sweating and gasping for breath and injured by crushing, and with the bodies of the dead. One person in the corridor managed to shatter the glass in the door, allowing a trickle of those trapped inside to escape.
Inside the lobby, some had smashed windows trying to escape the building. First responders were initially overwhelmed with the number of injured and dead, and over 50 ambulances were dispatched to the scene.
A total of 154 people lost their lives in the disaster, with the bodies of 119 people recovered from the hotel lobby and patio corridor, and an additional 35 having perished from injuries either en route to or after reaching the hospital. An additional 386 people were treated for injuries, approximately 25 of them being life-threatening.
Three days after the disaster, Charlie Dugan, a structural engineer hired by the Arvant Sun, discovered a significant change in the design of the walkways. The two walkways were suspended from a set of steel tie rods, with the second floor walkway hanging directly underneath the fourth floor walkway. The walkway platform was supported on three cross-beams suspended by steel rods retained by nuts. The cross-beams were box beams made from C-channels welded toe-to-toe. The original design called for three pairs of rods running from the second floor all the way to the ceiling. Investigators eventually determined that this design supported only 60% of the minimum load required by Arvant municipal building codes.
Freed & Sons Steel Company, the contractor responsible for manufacturing the rods, objected to the original building plan, since it required the whole of the rod below the fourth floor to be threaded in order to screw on the nuts to hold the fourth floor walkway in place. These threads would probably have been damaged beyond use as the structure for the fourth floor was hoisted into position. Freed & Sons therefore proposed an alternate plan in which two separate sets of tie rods would be used: one connecting the fourth floor walkway to the ceiling, and the other connecting the second floor walkway to the fourth floor walkway.
This design change would prove fatal. In the original design, the beams of the fourth floor walkway had to support only the weight of the fourth floor walkway itself, with the weight of the second floor walkway supported completely by the rods. In the revised design, however, the fourth floor beams were required to support both the fourth floor walkway and the second floor walkway hanging from it. With the load on the fourth-floor beams doubled, Freed & Sons' proposed design could bear only 30% of the mandated minimum load.
The serious flaws of the revised design were further compounded by the fact the both designs placed the bolts directly in a welded joint between two facing C-channels, the weakest structural point in the box beams. Photographs of the wreckage show excessive deformations of the cross-section. In the failure, the box beams split at the weld and the nut supporting them slipped through.