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Greg Gorbett spends unmeasured hours building scale-model rooms, complete with furniture and fixtures. He then judiciously stacks wood cribbing inside and burns his creations.
More often than not, he generates a fairly rare fire phenomenon called backdraft. Unlike the 1991 movie of the same name, Gorbett’s creations bellow soot-filled fireballs from inside high-temperature spaces that do not lend themselves well to moviemaking.
Gorbett, an assistant professor in fire and safety engineering technology at Eastern Kentucky University (EKU), also has experience working as a private consultant in fire, arson and explosion investigation. He specializes in fire behavior and fire dynamics. Gorbett and Jim Pharr, also an assistant professor in fire and safety engineering technology at EKU, said they have learned much about the phenomena of flameover, flashover and backdraft while firing the imaginations of students and colleagues alike.
Gorbett’s interest in backdraft started when he was researching other fire phenomena while working for a fire investigation firm. He said he became enamored with historical discussions of backdraft and how they related to an up-to-date look of the phenomenon.
“I found there was not much science concerning backdraft,” he said. “The foundation was set by (researchers C.M.) Fleishman and (P.J.) Pagni in 1993. Others have studied this phenomenon, but there are still some misconceptions out there. For example, some of the warning signs of backdrafts, which are based on firefighter common knowledge, tend to be on track. One of the items, a whistling sound, indicating an intended backdraft, might be a myth. We have not been able to replicate it.”
Others, such as a firefighter using a pike pole to break a window allowing air to rush inside a burning building and cause it to rapidly explode, are erroneous, he said.
“We have found in our quarter-scale-compartment burns that it can take up to 30 seconds for backdraft to occur,” he said. “So it’s not hard to imagine given a large structure – one that’s heavily divided inside – can allow firefighters to make a deep entry before a backdraft occurs.”
“Too often,” Gorbett said, “I have heard people misuse the terms backdraft, flashover and flameover/rollover. I felt that the science was much further along because of research performed on these topics, yet the practitioners in the fire protection profession seemed unaware of these studies.”
Further, the typical firefighter or fire safety professional will not want to digest a thousand pages of research data. And the past research was based on some less-than-real-world scenarios.
“That research had been done by allowing the compartment fire to go ventilation-limited,” Gorbett said. “Then researchers would inject excess methane or diesel fuel into the gas layer. When the event occurred, they would call it a backdraft. While their research was important, it did not seem real world, as most backdrafts occur due to Class A (common) combustibles. Therefore, we wanted to develop a way to show a backdraft occurring under real-world conditions that could explain the phenomenon without having a thousand pages of research data. So this is what spurred us to create the quarter-scale and half-scale compartments for demonstration purposes.” (See http://www.youtube.com/watch?v=uLyU40MX7tA&feature=youtube</a>.)
Not only have Gorbett and Pharr produced groundbreaking research, they have debunked a few myths. These are valuable to fire service students and firefighters alike. Many of the warning signs the fire service uses are generally accurate, they contend, such as the building looking like it is breathing, soot-stained glass and pressurized smoke.
“The only warning sign that we have not seen is the greenish color and the whistling sounds around doors and windows,” Gorbett said. He added, “There are two big myths that are consistently repeated by fire service manuals, textbooks and magazines”: