A diver can also use a demand valve with air supplied by a hose from the surface. This equipment, surface-supply breathing apparatus (SSBA), restricts the diver’s range and depth to the length of the air supply hose. Its advantages are that the diver is freed from the cumbersome air cylinders and the air supply can be as large as needed, instead of being restricted by the diver’s carrying capacity and need for mobility. The air for SSBA may be stored in large tanks or compressed as required. The use of a compressor, often called a ‘hookah’ system, is economically attractive because the air is compressed to a lower pressure than that required for storage tanks. However, the compressor needs to be reliable and there needs to be an observer to monitor the compressor during operation.
Two modified forms of SSBA have found support in some circles. In one, a small motor and air compressor are supported on a float on the surface. This apparatus supplies air to one or two divers. In the other, the divers tow a float that supports an air cylinder. An advantage of these systems is that, if the hoses are short, the divers are unable to reach the depth needed to develop decompression sickness (DCS). A significant problem is that the user has no indication of when the gas supply will fail. Therefore, it is prudent for the diver to carry a small bail-out cylinder and regulator. Also, some novice users may forget that they are still exposed to the other hazards of scuba diving, such as pulmonary barotrauma.
In some resort areas, these devices are hired by novices who have had no training and who may be medically unfit to dive. Such use should be controlled and monitored in a similar manner to normal scuba instruction and equipment hires.