Investigators with the Occupational Safety and Health Administration spent Friday combing through the explosion site at Crocker Park in Westlake, and interviewing workers and witnesses.
OSHA told newsnet5.com it is looking at all aspects of the construction site under its liquefied petroleum guidelines.
Nationally known fire investigator Bob Comer explained the fire and explosion may have been caused by an initial gas leak that created flames causing the liquefied propane to boil.
The mounting pressure and heat then caused the explosion.
"Leaking gas got ignited, which caused the fire around the tanks that heated the tanks and caused the explosion," Comer explained. "So was there security? And the big question is: why didn't they fix the leaks?"
Several teams of investigators were also on the scene of a construction site fire and propane tank explosion in that happened late Thursday morning. A structural engineer, BCI investigators, State Fire Marshal and OSHA investigators were on the site Friday.
Fire officials have not said what sparked the initial fire that caused one of two propane tanks to explode, damaging three floors of the American Greetings building that is under construction.
A State Fire Marshal declined to comment on his initial findings Friday.
A spokesperson for AmeriGas confirmed that the company had two 1,000 gallon propane tanks on the premises for temporary fuel during construction. The tanks were then leased by Walsh construction company.