Unraveling a 9-11 mystery


Fallout: The collapse of 7 World Trade Center presents a challenge to century-old fire tests still used in building design.

May 09, 2002|By Michael Stroh | Michael Stroh,SUN STAFF

Last week the team of engineers assigned to investigate the World Trade Center wrapped up its investigation, leaving more questions than answers. And one of the biggest is this: What happened to the building known as No. 7?

Sometime during the morning of Sept. 11 - experts still don't know exactly when or why - 7 World Trade Center caught fire. At 5:20 p.m., after burning unchecked through the day, it crumbled to the ground.

The building, which as far as anybody can tell sustained only minor damage from the attack, is the first fire-protected steel structure to collapse in a blaze. As a result, the formerly anonymous 47-story high-rise has become the center of a scientific whodunit that's calling into question some of the century-old fire tests used to design buildings today.

"We didn't find anything to say, `Look, this was definitely wrong,'" says Ramon Gilsanz, a New York structural engineer who led a seven-month investigation of 7 World Trade Center. "As far as we can tell, it was properly built and properly designed."

And that doesn't sit well with engineers, who want answers. So No. 7 and the twin towers will be the focus of a proposed two-year investigation by the National Institute of Standards and Technology in Gaithersburg. Solving the mystery, NIST Director Arden L. Bement Jr. told lawmakers last week, "could lead to major changes in both U.S. building and fire codes."

Doubt cast on tests

The mystery is already forcing experts to rethink the science underlying fire-resistant building construction in the United States - in particular a test known as ASTM E119. The test, developed in response to the Great Baltimore Fire and other catastrophic conflagrations of the day, is used to determine how materials such as steel stand up to the ravages of flame. First introduced in 1908 by the American Society for Testing and Materials, ASTM E119 has influenced the construction of the World Trade Center and most steel high-rises today.

The test works like this: Engineers place the building material - a steel girder, a concrete column, a section of roof or floor - inside a brick furnace and fire it up. As the temperature inside gradually rises, they record when the material begins to show signs of stress.

Some grumbled long before Sept. 11 that ASTM E119 was a fantasy fire and doesn't even come close to mimicking the way things burn in a real blaze. But few experts felt a pressing need to replace the test - mostly because it seemed to work.

"Our history has been excellent up until 9-11. We never had a collapse of a protected steel building," Jonathan Barnett, a fire protection engineer at Worcester Polytechnic Institute, told lawmakers last week.

Until now. After what happened to 7 World Trade Center and the twin towers, in which fire was found to be the major cause of collapse, critics of the test are starting to grow. "This is of great concern to us all," Barnett said.

One of the biggest criticisms of E119 is that it tests only individual components of a building - not the welds and joints that connect them. The other problem, say engineers, is that the test hasn't changed much since it was invented and so doesn't reflect the way things burn in an actual blaze. Especially when it comes to the "fuel load" - the term fire protection engineers use to describe everything from the wallpaper to wastebaskets inside a building that feeds a fire.

Fuel load tests were pioneered in the 1920s by Simon Ingberg, head of the Fire Resistance Section at the Bureau of Standards, NIST`s predecessor. To conduct his tests, Ingberg constructed a mock-up of a typical office building, raiding other departments for desks, chairs, trashed papers and similar office offal to furnish his laboratory.

Then he lit a match. For other tests, he would ignite abandoned buildings in Washington to measure the fire-resistant properties of brick walls, floors, combination safes and other items that needed to be able to withstand flames. During one 1928 experiment on the site of the present-day Justice Department, a reporter, seeing smoke and thinking the city was on fire, ran to its source and was shocked to find "most of the firemen gazing idly at the conflagration." Some squirted water on the ground or nearby buildings. "Every place but the fire," he wrote.

The results of many of Ingberg's experiments found their way into U.S. building codes. (When he was told to turn over his matches on the eve of his 70th birthday, the father of fire research turned his garage into a furnace so he could continue collaborating on tests with his former colleagues.)

`Much hotter fire'

But do tests conducted in an era of wood filing cabinets hold up today? Some engineers think not. "Building contents have changed a lot from the 1920s," says Shyam Sunder, the engineer in NIST's Building and Fire Research Laboratory who will lead NIST's in-depth investigation of the World Trade Center if Congress approves the money for it.

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