You could always use that as an exercise within itself- give a scenario of an accident occurring, and ask what they feel would help the investigation be as fruitful as possible?

In a previous role there was talk of an accident investigation kit, which would be a bag or box file with bits and bobs in that could be useful in an investigation ie pad and pens for statements if there are multiple witnesses, investigation forms, first aid forms in case the first aider doesn't have any, barrier tape, a camera, ruler or some kind of measuring device to give scale in photos, bags in case of any evidence you are able to collect, cctv request forms for managers etc