Be sure to notice that this question is not asking about training someone in your field, but training someone with specific regards to safety. Think about whether you have a specific technique for teaching someone, like having them follow you around while you point out safety aspects of your job, or start with a checklist of safety measures you take every day, etc. You want to make sure the interviewer understands that you are active in searching for ways to keep the workplace safe, including training others in the area of safety.