OH's accident in the street where he broke his kneecap was just that, an accident. Haveing worked in insurance in industry for many years, I know well that unless the employer can be held as negligent for keeping an unsafe workplace or permitting unsafe practices, the injured person can't take forward a successful claim. If you trip due to your own poor balance or fall over your handbag (for example) it's not the employer's fault.
I'd be interested to know the circumstances the OP is describing, just so we can have a better picture.
Today's blame culture has a lot to answer for, people are always looking for someone to provide compensation. Whatever happened to "being responsible for your own actions"?