Hi Richard
Just to clarify, we are not talking about criminal law here this is about a civil case where the burden of proof would be to prove "that on the balance of probabilities " i.e. just prove 51% of the argument and you have won the case. Regarding what goes on in my own jurisdiction i.e. Ireland most skippers will have you sign a legal waiver form before you set foot on their boat, whose goal is to precisely remove this threat of a civil claim against the skipper. Likewise with any course you undergo the Instructor usually produces a catch all legal waiver document on behalf of them and their training agency for the exact same reason.
In the context of the above mentioned case where an incorrectly labelled cylinder is given to a diver by a skipper, I'm not sure how the fault can in anyway be attributed to the skipper as he would say he is merely the 'busdriver' i.e. he would not have had any dealings with the analysis and labeling of the cylinder. Usually its the diver themselves who would have done this. But in any event if there was a case where another diver analysed and incorrectly labelled a cylinder and then gave it to a diver to breath where there was a resulting harmful event to the diver the only criminal offence in Ireland that comes to mind is Section 13 of the Non Fatal Offences Against the Persons Act 1997:
"Endangerment.
13.***8212;(1) A person shall be guilty of an offence who intentionally or recklessly engages in conduct which creates a substantial risk of death or serious harm to another.
(2) A person guilty of an offence under this section shall be liable***8212;
(a) on summary conviction to a fine not exceeding £1,500 or to imprisonment for a term not exceeding 12 months or to both, or
(b) on conviction on indictment, to a fine or to imprisonment for a term not exceeding 7 years or to both."
All the best