Science Casts Doubt on Arson Convictions

This photo, provided by the Lee family, shows Ji Yun Lee when she was in the 12th grade during a visit to Washington, DC. Lee's father, Han Tak Lee, a Korean immigrant, is serving a life sentence in a Pennsylvania prison for setting a fire at a cabin that killed Ji Yun in 1989. Many fire investigators now believe that the evidence used to convict him is scientifically inaccurate. (AP Photo/Lee Family) (AP)

"There were a lot of rules of thumb, but very little scientific understanding," said Jonathan Barnett, a professor of fire protection engineering at Worcester Polytechnic Institute and a leader in the investigation of the World Trade Center collapse.

Once researchers began to apply the scientific method to beliefs about fire, they fell apart.

A major revelation came from greater understanding of a phenomenon known as "flashover." When a fire burns inside a structure, it sends heat and gases to the ceiling until it reaches a certain temperature _ and then in a critical transition, everything combustible in that space will catch fire. Instead of a fire in a room, now there is a room on fire.

When that happens, it can leave any number of signs that investigators earlier thought meant arson _ like the burn holes on the floor that used to prove multiple starting points. And it can cause a fire to burn down from the ceiling _ not up as investigators had been taught.

Significantly, flashover can create very hot and very fast-moving fires. And it can occur within just a few minutes, dashing the concept that only arson fires fueled by accelerants can quickly rage out of control.

And the crazed glass? It comes from water being sprayed on hot glass, not a hot fire. The collapse of bed springs and the "alligatoring" _ they can't say anything definitive about a fire's cause.

The studies began to chip away at the old beliefs _ critics call them myths _ but it took years. Through the 1980s, texts at the National Fire Academy in Emmitsburg, Md., still taught the traditional techniques.

It wasn't until 1992, when a guide to fire investigations by the National Fire Protection Association _ "NFPA921: Guide for Fire and Explosion Investigations" _ clearly laid out, in a document relied upon by authorities nationwide, that the earlier beliefs were wrong.

"It's not that they're bad investigators or there's been any conspiracy to promulgate erroneous conclusions _ it's just the way it was," says Custer, the former associate director of the national Fire Research Laboratory and one of the principal editors of the 1992 guide.

"How many years did we think the Earth was flat?"

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In the calm, cool hours before daybreak on July 29, 1989, firefighters carefully put the charred remains of Ji Yun's body onto a blue sheet. Investigators quickly became suspicious.