Complex sentence: This fire was an indirect consequence of the bombing raids: because of the destruction inflicted on the Palais, the building had suffered from damp, which was treated with welding torches, and poor handling of these caused the fire.
Split into simpler sentences: This fire was an indirect consequence of the bombing raids: because of the destruction inflicted on the Palais, the building had been infiltrated by humidity. The subsequent moisture was fought with welding torches, and a bad handling of these caused the fire.