As a certified rescue diver you have no legal obligation to help anyone in trouble. Moral obligation maybe, but not legal. I am a rescue diver, instructor, firefighter, and a paramedic. Even if someone drops dead in front of me on a dive boat, legally I can just sit there and watch. I don't have to do a thing..... The only diference is if you are being PAID to act in an emergency response capacity. So if you are being paid as a rescue diver, DM, instructor, etc then yes you have to act accordingly. However, remember rule one "Rescuer safety first". If it is too dangerous for you to help, don't. There is no law that says you have to risk your life to help someone. Hate to say it, but it's better to have one dead diver and the end of the day then two or more.
I would have to disagree. As to my post above, if you are trained in all of the areas as you have stated you do have an obligation to assist someone in need if you have the capacity to do so.
If you are an instructor and you have two people on a vacation dive on the same boat as you and you hear them planning to go to a depth of 150ft you better speak up. Your training as an instructor should set off an alarm. You can't simply look the other way at something you KNOW is wrong.
Paid or unpaid, do you have a capacity to assist in a situation? If the answer is yes and you fail to do anything I'm going to bet that you would be hauled off to court. I also bet that your certification as an instructor would be suspended and I'm sure your paramedic career would also be at risk. You are a dive professional and should carry yourself as one.