updated 7/21/2004 11:04:43 AM ET 2004-07-21T15:04:43

Federal investigators analyzing evacuation patterns at the World Trade Center estimate more people than previously thought died below the areas hit by the hijacked planes.

The National Institute of Standards and Technology is conducting an extensive review of the collapse of the towers. Between 567 and 610 people died below the impact floors, “somewhat higher than previously thought,” lead investigator Shyam Sunder said Tuesday.

The NIST has tried to determine where people died to better understand evacuation responses and craft recommendations that would make skyscrapers safer.

The agency’s interim figures estimate 1,466 building occupants died in World Trade Center Tower 1, the vast majority — 1,356 people — at or above the impact site. In Tower 2, the second to be struck, 624 office workers were killed, and only six of those were below the impact site. More than 400 emergency responders were killed in the twin towers below the impact floors.

NIST also has determined 30 other people were killed in the towers below the impact sites, without being able to say which building they were in.

Sunder said between 1,974 and 2,017 people died at or above the areas of impact, a figure slightly below previous estimates. He said the shift may be explained by the lowering death toll since the first calculations were made in 2002. NIST said it still had no information on where 17 people died.

Altogether, 2,749 people died at the World Trade Center, including those on the hijacked planes, the agency has found.

Hundreds of interviews
The main source of information for the analysis came from 300 in-person interviews conducted by the NIST and about 800 phone interviews.

In many cases, the agency was able to use employees’ building identification information to determine on which floors they worked. That information was cross-checked against survivor accounts of their evacuations.

The investigators also tallied information gleaned from press accounts and a Web site dedicated to victims of the Sept. 11, 2001, attacks.

The agency had previously estimated that between 16,200 and 18,600 people were in the buildings.

It also determined 18 bystanders or occupants of nearby buildings were killed.

The institute’s investigation began two years ago in an effort to determine why the towers collapsed and use those lessons to recommend improvements in building codes, evacuation procedures and other standards. Its final report is due in December.

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