I don't think you'd need anything other than pointing out that the person refused to take minimal precautions, even though it was available to them. I'm pretty sure employers have been sued for this one - not doing the basic minimum to keep others safe.

Civil courts, at least in the US, don't need proof beyond a reasonable doubt, after all - which is why you can get found not guilty for felony charges but still have to pay a wrongful death settlement for the same incident.