Probing Trade Center Collapse

(AP)  The investigation into the collapse of the World Trade Center has been hampered by the destruction of steel wreckage that could hold vital clues about why the twin towers fell, a fire expert says.

Glenn Corbett, a fire science professor at John Jay College, criticized New York City's decision to melt down and recycle tons of charred and twisted steel from the trade center.

Corbett was among witnesses planning to testify Wednesday before the House Science Committee, led by Rep. Sherwood Boehlert, R-N.Y. Boehlert called the hearing to determine what can be learned from the collapse of the towers after they were struck by a pair of hijacked jetliners Sept. 11.

In testimony prepared for the hearing, engineering and government experts called for a re-evaluation and possible strengthening of building codes to prevent such catastrophic collapses. Additionally, fire ratings for building materials date from the 1920s and do not take into account new kinds of fuel and accelerants. Those ratings new need study, the witnesses said.

Other disasters, such as the Northridge earthquake in California and the bombing of the federal building in Oklahoma City, have led to changes in building codes.

The National Institute of Standards and Technology Building and Fire Research Laboratory says the Trade Center collapse raises questions about current codes governing concrete design and structural integrity and is redirecting federal dollars to augment research in those areas.

Boehlert said more research dollars will be needed to fully investigate and analyze needed improvements.

Experts also planned to complain about the delay in obtaining blueprints, design drawings and maintenance records from the building owners and insurers worried about liability. Such resistance has slowed the investigation, they said.

The investigation into the trade center collapse is being conducted by the Federal Emergency Management Agency and the American Society of Civil Engineers. A FEMA assessment team is expected to release a report of its findings in April.

The team has been examining frame-by-frame footage of the 110-story collapse. Such details could allow them to determine whether the core columns fell first, dragging each floor with them as they fell. Another theory suggests that the exterior columns pulled inward, giving in to floor joists weakened by raging fires.

Some victims' relatives have called for a broader federal probe of the collapse that would investigate factors in addition to structural failures, such as evacuation procedures. And even some engineering experts have raised questions over whether the lightweight steel trusses that supported individual floors and possible fireproofing flaws may have made the twin towers vulnerable to collapse.