Complex sentence: The explosion manifested itself in a volume of flame and dust at the number two or downcast shaft, followed seconds later by a volume of flame from the upcast or number one shaft which set fire to the wooden sheds or headings above it.
Split into simpler sentences: The explosion manifested itself in a volume of flame and dust at the number two or downcast shaft. Followed seconds later by a volume of flame from the upcast or number one shaft which set fire to the wooden sheds or headings above it.