Federal resources are in Tulsa investigating a fire that injured several firefighters.
The Tulsa Fire Department and the Alcohol Tobacco and Firearms met Thursday night about Wednesday's fiery explosion at the old Barnard Elementary school building.
They laid out the plan of action for Friday, when they start collecting evidence at the scene of the fire.
The Tulsa Fire Department has left the scene as is to preserve any evidence at the building which was most recently renovated to house the Tulsa School of Arts and Sciences.
TFD Chief Stan May said we use lighter products now, that are actually more flammable, to renovate older buildings.
May said they want to be very careful with this investigation, because a lot of people are watching.
"People from all over the country are interested in this, also, because it was a very large explosion, but there are literally thousands of these types of buildings with that type of structure," May said.
A security guard and one fire truck has been at the scene since the explosion that injured eight firefighters.
News On 6 has learned one firefighter was re-admitted to the hospital last night, because he was having problems with his pain medicine.
He and two other firefighters will remain in the hospital until at least Monday.
Fire officials say they have burns on their ears, sideburn areas, legs, hands and backs.
May said their fire gear may have saved their lives.
"It's got the highest fire rating that we can get and, yeah, had we been using old gear or something that is not quite up to standard, we could have had a lot worse," May said.
Investigators hope the extra federal resources will answer why the firefighters were injured in the first place.
The ATF will bring in its chemist, engineer and search dog to assist.
"We're looking at it, not so much from a crime scene aspect, but, ‘Why did it happen?' We've been getting phone calls from around the nation, other fire departments wanting to know what we thought caused it, and this will help clear that up," May said.
Tulsa Fire and the ATF will head out to the fire scene at 8:00 p.m. Friday.