Surface-supplied-air and mixed-gas diving has many advantages over traditional SCUBA-gear diving. Divers utilizing a hard hat and surface-supplied air or mixed gas are continually tethered to the surface. In this mode of diving, air for breathing is normally supplied by a surface compressor, fed through a volume tank, and delivered to the diver through an umbilical.
In addition, in surface-supplied-air and mixed-gas diving, a back-up supply of air, normally contained in a high-pressure bottle, is plumbed into the system for use in an equipment failure. Divers also commonly wear what is referred to as a “bail-out bottle,” a SCUBA bottle that can provide air in the event that the first two systems fail. These redundancies significantly elevate the safety of the divers.
The diver’s umbilical includes a communication cable, which allows clear and constant communication between the diver and surface personnel, and a pneumofathometer hose, which permits constant monitoring of the diver’s depth and also provides yet another source of air to the diver in an emergency. The umbilical can also provide electricity to power underwater lights and a helmet-mounted underwater camera, for real-time monitoring and recording. Finally, the umbilical includes a hose that can supply hot water to a diver’s hot-water suit, enabling a diver to remain at the work site far longer and to work more comfortably and efficiently.
These features make surface-supplied-air and mixed-gas diving far superior to SCUBA diving in terms of safety, efficiency, and versatility. The commercial diving industry maintains a strong preference for surface-supplied-air and mixed-gas diving in all but a few rare situations.