"Flashover is a transition point where you go from having a fire in a room to a room on fire," Lentini said.
But what you see after a fire has exploded into flashover is even more important to our story. Lentini guided us through the ruins after the fire was out.
"If you see a pattern on the couch, that looks like it's where it started," Lentini said. "'Cause there's a 'V' [a V-shaped burn pattern] over there, and there's a 'V' over here. You say, 'Well, that could be two points of origin.'"
The appearance of multiple points of origin in a fire has traditionally been regarded as "slam-dunk" evidence of arson, Lentini said.
It was such a slam-dunk that helped put Bunch in the slammer. During Bunch's trial, the prosecution used photos showing burn patterns as evidence of multiple places of origin.
"That is 100 percent inaccurate," said Raley, who is working for a new trial. "One hundred percent wrong. One hundred percent fiction."
When Bunch was convicted in 1996, Raley said, flashover and the science of arson were not well understood. Bunch has now served 14 years in prison and has no hope of parole for at least 12 years.
The prosecutor in Bunch's case declined our request for an on-camera interview, but he maintained that the jury made the right decision. He said that Bunch's behavior was questionable and that she made many contradictory statements during numerous police interviews. The jury made its decision on matters that go beyond the science alone, he said.
There wasn't much left of Bunch's trailer after fire swept through it, killing her son, Tony, 3, in June 1995. What was left, according to fire investigators at the time, was unmistakable evidence of arson.
"The arson conclusion was made within two hours of the investigators arriving at the trailer," Raley said. "The first investigators arrived around 8 o'clock in the morning. By 10 o'clock in the morning, there had already been a conclusion."
That conclusion was that Bunch had poured accelerant in her son's bedroom, touched off the fire and let him die. "I am never going to stop fighting, never going to stop trying to prove that I didn't do this," Bunch said.
Prospects for a new trial for Bunch may depend on one woman, Jaime McAllister, an expert in the emerging field of combustion science. McAllister's opinion about the prosecution's original arson case can be summed up in four words.
"Their theory is impossible," she said.
An autopsy report on the little boy's body showed he died with 80 percent carbon monoxide in his blood. That's an impossibly high number, McCallister said, if the fire had been set in his room.
"You couldn't breathe in that amount of carbon monoxide and get to that level of 80 percent before you would die from the heat," McAllister said.
Tony Bunch was dead, she said, long before the flames got to him.
Basic science suggested the fire started in an unventilated place, like in the space between the ceiling and the roof, where there were electrical wires and a malfunctioning light, McAllister said.
A short in the wires could have overheated the ceiling tiles.
"As that smoldering occurs, it produces a lot of products, like soot and carbon monoxide," McAllister said. "And they would start to leak out in the room."