Thanks Blue Eagle, however.......To cut the strap, yes you have to find the knife, the thing is where is the knife positioned, imagine it is dark and only the light from lightning is available plus emergency lighting is on in the cabin giving some light, the raft is pitching in five foot waves, where do you look? In the incident I was involved in (42 years ago) the dinghy I was in was tied to the aircraft, but we were not aware of this at the time and after trying to paddle away from the aircraft frantically for a few minutes (that seemed like hours) it was myself that had spotted a thin nylon(?) cord attached to the fuselage, the knife apparently was in a sheathe which was floatable and attached to the dinghy, none of us knew there was such a device handy. Only by good fortune that in my dinghy, there was a Royal Marine Commando on board as a pax, he pulled a knife from his sock and severed the cord.......this then enabled us to paddle away from the still floating aircraft. I have since found two Flight Engineers who last year informed me that the cord was designed to sever by 'breaking strain' when the aircraft sank, thus leaving the occupants of the dinghy free to escape to safety. The aircraft stayed afloat for twenty minutes before sinking to the abyss, we by this time was some 200-300 yards off the tailplane.
I expect today things have moved on apace and that such knives are to be found in a DAY-GLO holder. I might just add that most crew are trained for such emergencies, presumably, but in reality it is the shear fear and 'organised chaos' that sees you through the event!