A production shutdown system for an underwater hydrocarbon production facility, comprising, on the topside:a safety system, anda communications module;and, underwater;drive control means, andan underwater communications component;wherein in use safety signals are passed from the safety system to the drive control means via the topside communications module and the underwater communications component, and wherein the safety system and drive control means are rated according to a prescribed safety level but the communications module and underwater communications component are not so rated.