Comment by ddls

What instructors and dive-masters actually do (or should / are trained to do) for those dives is hold onto the first stage regulator at the top of the tank for the entire duration of the dive and never pass 12 meters. The diver never even needs to worry about buoyancy. We use to call them Lipton (tea) dives, because it was just dipping tourists into the water ;) They are absolutely 100% safe when done according to the requirements.