I agree absolutely that thorough safety briefings should be carried out for OBVIOUS reasons. It also sets a professional tone before we begin work and ensures that everyone DOES know their safety. It also is a way of constantly refreshing ourselves in prepation for our annual SEP's. Not everyone can be trusted to read their manual for 10 mins a day. I've done briefings many times and found that people have been way off the track so it's a good way of maintaining knowledge. Cocky people who think they 'know it all' can often be the dangerous ones.
