Helmets? Has anyone mentioned helmets?
You're asking for trouble if you're going underground without helmets: it's not so much the fact that you might bang your head on the roof, but rather more that you're halfway down a pitch when one of your clumsy acquaintances inadvertently knocks a load of rocks down onto your bonce from the pitch head.
Also, Croesor is a rather crumbly mine with a history of bits of roof falling off. In reality, most of what might fall down is so big that whether or not you were wearing a helmet will have made no difference at all, but it will at least keep all the squidgy bits of your head in the same sort of place.
Of course, if you happened to be lucky and only have a small piece of roof land on you, then the helmet might have proved vital.
Hello again darkness, my old friend...