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Checking towers' steel in Sept. 11 probe

Scientists in Md. study durability of structure in trade center attacks

By Dennis O'Brien
Sun Staff

December 4, 2002

GAITHERSBURG -- Researchers probing why so many people died in the World Trade Center towers are busy examining a variety of steel that was used in the buildings and rescued from New York landfills after the Sept. 11 attacks. 

But of the 200 steel columns, trusses and bolts that were salvaged by the National Institute of Standards and Technology for its study, one column stands out. 

Column A-130 -- hanging nearly intact on a wall in a cavernous building here -- was where the first airliner hit on the north side of the North Tower between the 93rd and 96th floors. 

NIST researchers say the column could yield clues as to what caused the towers to collapse. 

"We're lucky to have it. But then, we're really lucky to have all of what we have because there's a tremendous amount of material to work with," said Frank W. Gayle, deputy chief of the NIST's metallurgy division. 

Gayle said that every column in the towers was marked with a serial number and that the builder's schematic drawings show where each was placed. 

NIST officials say that column A-130 -- along with others that are as twisted as spaghetti in a bowl -- will be closely examined as part of the most detailed study yet to determine what started the fires, how they spread, and the sequence of events that led to the collapse of the towers and the deaths of 2,823 people. 

The goal, according to researchers, is to reduce damage and injuries in future fires and building collapses. 

"The key question is, can we find areas where improvements can be made to existing buildings? Can we better assess the risk to buildings so that a building's owner can decide what safety measures are necessary?" said S. Shyam Sunder, the civil engineer who is leading the investigation. 

Along with the tower structural failures, researchers will examine failures in the communications and fire protection systems and the adequacy of evacuation procedures. They will also review whether a different building could have withstood the crashes and whether different types of steel, fireproofing or other materials would have kept the towers standing longer. 

The study is expected to take two years, and employ about 24 members of the NIST staff and about 24 private consultants. Sunder said he knows the issue is emotionally charged and that the study's conclusions will be closely examined. 

"We know this is going to be a major undertaking, but we hope the science that we use will help answer the questions that are out there," he said. 

Relatives' questions 

The work is being closely watched by relatives of those killed in the attacks -- some of whom have sought such a study since the towers' collapse. 

"I want to know why my husband was crushed," said Monica Gabrielle of Skyscraper Safety, a New York-based survivors group. 

Gabrielle said she learned from 911 tapes and survivor accounts that her husband was killed in the South Tower after a wall fell and crushed his legs while he waited for an elevator on the 78th floor. The firefighters who reached him also died in the collapse, she said. 

"These buildings tumbled like a house of cards, and that's something that deserves investigation," she said. "If we can fix what went wrong, that'll be their legacy." 

NIST officials say the study -- the second and more comprehensive federal probe into the tower failures -- will include computer modeling of how the fires spread. 

"We're going to know an awful lot about buildings and fires and impacts that we didn't know before," said Richard J. Fields, an NIST metallurgical engineer. 

Fields said that next month his crew will start testing the durability of the 14 types of steel used in the towers. They will rely on a Kolsky Bar -- a tool used by automakers and other manufacturers to measure the effects of pressure on metal. It consists of an air gun and two steel rods. 

Researchers will cut shards from the towers' steel columns, carve them into dime-sized pellets and place them between two of the bar's steel rods. They will then fire bulletlike projectiles from the air gun at one rod, which will send the rod crashing against the test pellet with the force of the jetliners that hit the towers at 500 mph. 

>From the tests, researchers hope to reconstruct what happened to the structural steel when the planes hit. 

"We want to know what damage the planes did inside the buildings, where did the planes come to a stop and where did they drop their fuel," Fields said. "Nobody knows exactly where the fuel actually went." 

Ronald Rehm, the researcher overseeing the computer models, is trying to determine how the fires spread by factoring the wind speed and direction on Sept. 11 to calculate the "heat-release rate" of the fires started by the airliners' impacts. 

Rehm said that based on computer modeling, the fires created about the amount of power generated by "a good-sized power plant." 

He also confirmed what has been known by experts who have studied the collapses -- that the aviation fuel burned up within minutes. It was the paper, office furnishings and other materials inside the buildings that fueled most of the fires. 

An investigation last spring by a civil engineering group and the Federal Emergency Management Administration found that the towers withstood the initial impacts of the airliners. But the impacts quickly destroyed escape stairwells and fire sprinkler lines, which were encased in centrally clustered lightweight walls, the study found. 

The FEMA report concluded that the fires' high temperatures softened the structural steel to the point of collapse and that the impact of the airliners and flying debris probably jarred loose spray-on fireproofing from the towers' beams and trusses. 

The North Tower, which had 1 1/2 inches of fire retardant on the steel supports, fell in 104 minutes and the South Tower, which had 3/4 -inch fireproofing, fell in 56 minutes, the report noted. 

Following up on those earlier findings, NIST researchers say they will be looking at the amount of fireproofing in the towers to see if it was adequate. 

Survivors' interviews 

Critics have faulted FEMA for not interviewing survivors on how the fire spread and for not focusing on evacuation procedures and the emergency response to see if they were adequate. 

Sunder said that unlike the FEMA review, the NIST study will include a thorough review of building plans and interviews to hear of survivors' experiences. 

Laws passed since Sept. 11 have given NIST the authority to investigate major structural failures and the power to subpoena building plans from owners, architects and contractors. Sunder said he hasn't had to use the subpoena powers. 

Building plans and records have been supplied voluntarily by the engineer who designed the towers, Leslie E. Robertson, and the owner of the building, the Port Authority of New York and New Jersey. Experts for the tower insurance firms, hired to assist with lawsuits filed in the wake of the attacks, also have come to the NIST campus to brief researchers, Sunder said. 

"We're getting excellent cooperation," he said. 

One goal of the study, Sunder said, is an update of fire safety standards for building materials. The standard test for how steel or other building materials will stand up to a fire was developed in response to the Great Baltimore Fire in 1904 and introduced in 1908. The material is placed in a brick furnace, the furnace is fired up and the temperature is recorded when the material begins to show signs of stress. 

"We don't have modern equipment to test for fire safety of materials the way we should have. When it comes to fire ratings, not much has changed in 80 years," Sunder said. 

Copyright (c) 2002, The Baltimore Sun

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