Complex sentence: A stagehand tried to douse the fire with the Kilfyre canisters provided, but it quickly spread to the fly gallery high above the stage where several thousand square feet of highly flammable painted canvas scenery flats were hung.
Split into simpler sentences: A stagehand tried to douse the fire with the Kilfyre canisters provided, but it quickly spread to the fly gallery high above the stage. There, several thousand square feet of highly flammable painted canvas scenery flats were hung.