Complex sentence: The night porter was alerted; against instructions he didn't call the fire department immediately but unsuccessfully poured some buckets of water in the shaft, and by the time he decided to call the fire department the hotel was already filling with smoke.
Split into simpler sentences: The night porter was alerted; against instructions he didn't call the fire department immediately poured some buckets of water in the shaft, but was unsuccessful in stopping the fire. By the time he decided to call the fire department the hotel was already filling with smoke.