Surface-Supplied Diver Air Supply Rate and Reserve

A compressor sized for shallow work falls short in deeper water with no change in the number of divers and no warning that anything has changed. Two divers plus a standby at 100 ft, at 1.4 acfm each, need 16.9 acfm -- 5.64 per diver at 4.03 atmospheres -- and a 20 scfm compressor has 3.1 acfm of margin. Take the same spread to 190 ft and the requirement is 28.4 acfm: the compressor no longer meets it, with nothing changed but depth. THE OPERATIONAL LIMIT IS THE NUMBER WORTH HAVING. Working the relation backwards, that compressor supports three divers to 124 ft, and that is worth knowing before the job rather than at the dive station with divers dressed in. THE STANDBY DIVER COUNTS: a spread sized for the divers in the water is undersized. THE RESERVE IS A SEPARATE, REGULATORY CALCULATION. Surface-supplied diving requires an independent reserve breathing supply, sized to bring the diver to the surface from the maximum depth including any required decompression and available without the diver doing anything to switch to it. Ten minutes at 100 ft is 56 cubic feet against the 109 cubic feet of free gas an 8 cu ft tank holds at 200 psi -- so this one covers it, but a volume tank that meets the flow requirement and not the reserve requirement does not comply, and passing one is not passing. A flow and volume calculation on figures the user supplies. The rate per diver is entered because it is set by the applicable regulation and the operation procedures rather than by arithmetic, and the figure that applies depends on the jurisdiction, the mode of diving, and the depth. It does not size an umbilical, evaluate pressure drop along its length, or address the supply pressure the helmet or mask requires at depth, which is a separate and governing check. It does not evaluate air purity, which is its own testing regime, or compressor intake placement, filtration, and carbon monoxide risk. The applicable commercial diving regulations, the operation diving safety manual, and the diving supervisor govern.

required flow = the rate per diver x the absolute pressure (1 + depth / 33 seawater) x the number of divers including the standby; the deepest compliant depth = 33 x (compressor capacity / (rate x divers) - 1); the volume tank's free gas = its capacity x its pressure / 14.7 psi.

The surface-supplied flow relation by name, with the independent reserve breathing supply named as a SEPARATE regulatory requirement. The rate per diver is set by the applicable regulation, not by arithmetic. The applicable commercial diving regulations, the operation's diving safety manual, and the diving supervisor govern.

Flow arithmetic on the spread's own equipment figures; no regulatory table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: diver_count, depth_ft, rate_per_diver_acfm, compressor_scfm, alt_depth_ft, reserve_minutes, volume_tank_cuft, tank_pressure_psi, feet_per_atm, depth_ata, per_diver_acfm, required_acfm, compressor_margin_acfm, alt_required_acfm, max_depth_ft, reserve_required_cuft, tank_free_gas_cuft

• The standby diver counts a spread sized for the divers in the water is undersizedcommercial diving regulations
• Reserve is separate from flow meeting one requirement is not meeting the othercommercial diving regulations
• The rate per diver is regulatory it depends on jurisdiction, mode of diving, and depththe applicable regulation