PHILADELPHIA -- With most of the wooden planks, plastic chairs and other debris removed from the Delaware River where a nightclub pier collapsed, investigators planned to get a closer look at the damaged structure to determine what caused the fatal accident.
Engineers Saturday were to examine the site by boat before divers are sent under the dock to try and determine what caused Thursday's collapse, mayoral Chief of Staff Stephanie Franklin-Suber said late Friday.
Three women were killed. All but two of the 41 people believed to have been dropped into the river have been accounted for, Franklin-Suber said.
Six people remained hospitalized, though none of the injuries were considered life-threatening. Authorities don't know if the two remaining people simply have not checked in with officials.
''We're concerned and we're not going to give up until they're accounted for,'' Franklin-Suber said.
All of the 20 or so other piers that line the waterfront were ruled structurally sound by city inspectors late Friday. Mayor John Street ordered inspections of all the piers, many of which are believed to be 100 years old. The former industrial area along the river is now dotted with restaurants and nightclubs catering to a college-age crowd.
On Thursday night, people at the open-air nightclub Heat said they had almost no time to react when Pier 34 began falling away under their feet. One victim said the frantic scene was similar to one in the movie ''Titanic,'' in which people ran up an inclined surface as it sank into the water.
Those dropped into the river desperately tried to reach the surface through a mess of wooden planks and plastic furniture. An overhead canvas tent fell into the water, blanketing them.
One of the club's employees, Lawrence Price, said he saw a four-inch crack on the pier that he was told to cover with sheet metal Thursday.
Killed were DeAnn White, 25, of Philadelphia; Jean Ferraro, 27, of Cherry Hill, N.J.; and Monica Rodriguez, 21, also of Cherry Hill. They were at the club celebrating White's birthday, which would have been Saturday.
The president of the company that owns Heat said he was working near the pier Thursday night and stayed on the scene through the night.
''I am distraught and saddened by the tragic accident at Pier 34,'' Eli Karetny, president of HMS Ventures Inc., said in a statement released Friday. ''My heart goes out to all our patrons and employees who were involved and their families.''
Karetny said he was cooperating with investigators.
The city is seeking help in the investigation from a forensic engineering firm that specializes in pier design, and the Army Corps of Engineers, responsible for the Delaware River shipping channel, also is serving as a technical consultant, spokesman Ed Voigt said.
The river was closed to all ship traffic Friday, but reopened overnight, with boats escorted by the Coast Guard.
Harry Harris, a Drexel University engineering professor, said many of the piers were originally built to support warehouses and should be able to withstand the weight of a night club.
''Some are in very bad shape and some are in very good shape, relatively,'' Harris said. ''It depends on the owner and what transpired.''
The nightclub opened this month next to the historic Moshulu.
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