The explosion was loud and violent, with a nearby neighbor feeling the full brunt of the shockwave.
"It's just like a sound percussion, kind of like a sound barrier, the initial boom," said Odie Newman.
Meanwhile, inside the plant, a pool of flame consumed everything in it's vicinity. What happened?
"They were moving a propane tank with a forklift, it fell off, I believe it broke a valve off, and started spewing propane," said Eufaula fire chief Clifford Shatswell.
The workers left immediately, with two of them returning later officials say, once they thought it was safe. In reality the building was now filled with propane, and to vent it out...
"They might have flipped an exhaust fan, which in turn would leave a spark and ignite anything that's up in the attic or the ceiling," said Newman.
"Quite a bit of third degree burns to I think from the waist up," said Eufaula mayor Selina Jayne Dornan.
As the blaze built, firefighters decided to evacuate the nearby elementary school as the thick, possibly toxic smoke, billowed from the scene.
"And that was why we evacuated the school because they had chemicals in there also they said and the cloud of smoke was headed towards the school, and also the propane people told us a half a mile sometimes is the danger of those 500 gallon tanks," said Eufaula police captain Charles Hammett.
The children were unharmed and relocated to the high school, while the two workers were life-flighted to a Tulsa hospital in critical condition.