In any civil action, the finder of fact may find the defendant not liable if the defendant proves that the claimant or, if the claimant is an heir or the estate of a deceased person, the decedent was under the influence of an intoxicating liquor or a drug and as a result of that influence the claimant or decedent was at least fifty per cent responsible for the accident or event that caused the claimant's or decedent's harm.
A.R.S. § 12-711