TULSA, Okla. (AP) -- Several days of triple-digit heat set off an unusual chain reaction that ended in a series of fiery explosions at a gas distributor last week, fire investigators said Monday.

The spectacular fire at Airgas Mid South's plant at 31 N. Peoria Ave. last month required a massive response from Tulsa firefighters. In all, hazardous materials units or fire companies spent 165 1 /2 ...