[MarkL]

Probably the propane tanks for the portable heaters used to warm up the interiors enough to allow drywall crews, tile crews and painters to work. Once they get hot enough the pressure relief valves of the propane tanks open and the propane in the tank ignites explosively.

There were certainly no heaters in operation today... The temperature was in the mid-80s today. Global warming and all that, it snowed less than a week ago.

Mark

[UCANSEE2]

There were certainly no heaters in operation today...

The point being made was NOT that the heaters were in operation, but that the propane tanks were there because it HAD BEEN very cold (19 degrees) just a few days ago.

There were two explosions, and it is very likely it was propane tanks in the building. It also could have been cleaning chemicals (like acetone). The first explosion was small (could have been the acetone), the second was much larger (likely the propane tanks).