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The ASPECT plane had been flying for just six years, but its crew had extensive experience collecting such data. After hurricanes Katrina and Rita, this same crew ran dozens of missions across the Gulf Coast to see whether there were dangerous chemicals in the path of flood waters. While flying over the Port of New Orleans, the crew once identified a single drum of chloroacetic acid, a chemical used in pharmaceuticals. The crew was able to alert officials on the ground about the drum before floodwaters engulfed it and contaminated the water with a potentially toxic chemical.
After four or five circles around the cloud, Brindle steered the plane westward. He needed to land the plane so EPA officials could decipher the data they had collected. But the cloud blocked the normal approach to downtown's Wheeler Airport. Brindle brought the plane in low near the West Bottoms, coming in at an angle to make the runway.
Waiting was EPA environmental scientist Mark Thomas, who grabbed the hard drive out of Leger's computer. Thomas brought the information to the EPA's lab in Kansas City, Kansas, where it took the computer 10 minutes to spit out a series of graphs. (The information produced in the EPA lab looked like a stock-market report, with peaks and valleys to help scientists determine a chemical's makeup.) Thomas then matched up the graphs to a book of chemicals, like comparing the lines in a fingerprint.
The process of matching up infrared charts to chemicals isn't perfect, so Thomas sent the charts to the Los Alamos National Laboratory in New Mexico. There, Robert Kroutil, a chemist who invented the ASPECT plane, did the same comparisons Thomas was making in Kansas. They got on the phone to compare notes.
Thomas and Kroutil found that the cloud contained low levels of three chemicals: ammonia, methanol and trimethylbenzene, or TMB. Thomas wasn't sure about TMB. "What is this stuff?" Thomas remembers wondering. Both of them hit their respective libraries to figure it out.
TMB is a chemical often used to make drugs and dyes, they learned. Exposure to it can affect the nervous system and cause fatigue. But based on the EPA's guidelines for exposure to TMB, the levels were low enough that scientists determined the cloud was safe.
By then it was almost 7 p.m. Thomas passed his findings on to EPA officials. The short answer: The plane had found nothing at hazardous levels in the cloud.
This was the first time that officials knew the cloud was safe for people in downtown. But Dyer had been telling the media for hours that there was no reason to fear the smoke.
Asked why he made his statements so soon, Dyer says, "That was based on my 40 years in the business." His experience, he says, led him to believe that the debris was made up mostly of roof material caught in the updraft. And he had been receiving information from the EPA and others about ground readings at the site. "To my mind," Dyer says, "we would have experienced a lot more panic if we had waited."
The EPA didn't correct Dyer's statement, the agency's Kroon says, because it was the fire chief, not the EPA, who made the statement. "When first responders show up, their goal is life safety," Kroon maintains. "We aren't second-guessing them."