Complex sentence: The large chandelier that was suspended in the ceiling of the theater started to swing, and the people inside, terrified, fled, when the spiral staircase cracked, causing many people to fall into the gap.
Split into simpler sentences: The large chandelier that was suspended in the ceiling of the theater started to swing. The people inside where terrified, so they fled down the stairs, but the spiral staircase cracked, causing many people to fall into the gap.