Complex sentence: Security Chief Harry Jernigan (Simpson) and Roberts are informed that Mueller has been seen on 87 and they head up to assist in the rescue of her and two children, but are halted as a gas line explodes in a stairwell.
Split into simpler sentences: Security Chief Harry Jernigan (Simpson) and Roberts are informed that Mueller has been seen on 87. They head up to assist in the rescue of her and the two children, but are halted as a gas line explodes in a stairwell.