Before revision: Bad Air : Old mine workings may be hazardous due to pockets of blackdamp (still air with low oxygen levels), or high concentrations of methane, carbon monoxide, carbon dioxide or hydrogen sulfide which can displace oxygen, poison someone outright, or create an explosion.
After revision: Bad air : Old mine workings may be hazardous due to pockets of blackdamp (still air with low oxygen levels), or high concentrations of methane, carbon monoxide, carbon dioxide or hydrogen sulfide which can displace oxygen, poison someone outright, or create an explosion.