I use a few accident videos - but these are copyrighted and so you would have to buy them unless you already have them - or try YouTube? The best though - is to use examples from the accident book, or better still recent investigations of more serious incidents. This not only makes them relevant but means you already have an answer too! Just ensure data protection and remove any personal information etc. It's also good to role play, and get people to interview, again this is easier if it's a real incident you have been involved in!

I don't know what industry your in or what level of accident you mean but if you research the "Piper Alpha" and "Deep Water Horizon" incidents there is a huge amount of information on Human Factors and management failings. If you mean more general workplace accidents then I agree with posters above, look at your accident records identify the most common injury and work on that regarding the way you get down to the root cause