Complex sentence: Lighting in the tunnel was provided by makeshift candles--digging tools and shovels were improvised out of British biscuit cans with handles made from the wooden slats of their beds.
Split into simpler sentences: Lighting in the tunnel was provided by makeshift candles. The prisoners used improvised digging tools and shovels that were constructed from British biscuit cans and their handles made from the wooden slats of their beds.