Planning for Safer Buildings

This is the VOA Special English SCIENCE REPORT.

Experts are beginning to study ways to secure large buildings against terrorist attacks. They are reacting to the attacks that destroyed the World Trade Center buildings in New York September eleventh.

The American Institute of Steel Construction has created a working group of experts to investigate the reasons the buildings fell. The A-I-S-C is the organization responsible for developing the rules for the design of steel buildings in the United States. Information developed by the working group will help A-I-S-C decide if the design rules should be changed.

The south World Trade Center building fell fifty-six minutes after a passenger plane crashed into it. The north building fell about one-hundred minutes after a similar crash. Each building was four-hundred-ten meters tall. Experts say the buildings could not survive the extremely hot fires caused by the airplane fuel.

Engineers think the airplane crashes destroyed part of the structure of the buildings that kept them standing. The resulting fire weakened the remaining structure. The buildings fell because the weight above the area where the planes hit was greater than the remaining structure could hold.

Building experts say it is possible to build a skyscraper that would survive such an attack. But they say the cost would be so huge that no one could pay for it. They also say that materials developed since the World Trade Center was built may give people more time to escape such a situation.

The building experts say the most important consideration is to slow the destruction caused by the fires. The World Trade Center's support structures were made of a strong metal, steel. The heat of the fires caused the steel to expand, weaken, and fail. Today, builders can use concrete that has steel bars inside. Concrete is a mix of cement, sand and small stones. Experts say it can survive better than steel alone can.

The two tallest buildings in the world are the Petronas Towers in Kuala Lampur, Malaysia. Each is four-hundred-fifty-two meters tall. They were built of concrete and steel. Experts say their structures could provide a better chance of surviving than did the World Trade Center buildings. They also say the escape areas of the Petronas Towers are treated to keep out smoke and fire.

This VOA Special English SCIENCE REPORT was written by Nancy Steinbach.