Recompression Chamber Gas Volume, Ventilation, and Duration

A 250 cubic foot chamber taken to 60 psig is 5.08 atmospheres absolute and takes 1,270 cubic feet of free air just to get to depth -- more than most people expect, and only 21% of what the treatment needs. VENTILATION DOMINATES because carbon dioxide from the occupants has to be flushed continuously and the ventilation rate is itself multiplied by the absolute pressure: 2 acfm each for two occupants at 5.08 ata is 20.3 cubic feet of free air a minute, which over a four hour treatment is 4,878 cubic feet. Total 6,149, of which ventilation is 79%. A supply sized on pressurization alone would cover about a fifth of the requirement. SIZE AGAINST THE LONGEST TABLE, NOT THE SHORTEST. A treatment table consumes gas out of all proportion to the chamber size, so the calculation has to cover the longest table the operation might run plus its extensions -- an 8,000 cubic foot inventory here supports 331 minutes, against the 240 entered, and a chamber with gas for a short table and a patient who needs a long one with extensions is a serious problem discovered under the worst possible circumstances. OXYGEN IS A SEPARATE INVENTORY: treatment runs the occupant on oxygen by mask with overboard dump, 610 cubic feet over two hours here, its own cylinder bank, and running out of it ends the treatment as surely as running out of air. A volume calculation on figures the user supplies. It does not select or validate a treatment table, which is a medical decision made by a diving medical officer, and it does not model carbon dioxide scrubbing, chamber temperature and humidity control, or the oxygen fire risk that makes chamber oxygen handling its own discipline. The ventilation rate entered is set by the applicable standard and the occupant load. It does not address chamber certification, pressure testing, or the operator qualifications required to run one. The applicable treatment tables, a diving medical officer, the chamber manufacturer, the operation diving safety manual, and the applicable regulations govern.

free air to pressurize = the chamber's internal volume x the absolute pressure (gauge psi + 14.7) / 14.7; ventilation air = the rate per occupant x the occupants x that same absolute pressure x the treatment duration; the longest supportable treatment = (inventory - pressurization) / the free-air ventilation rate.

The chamber gas relations by name. The applicable treatment tables, a diving medical officer, the chamber manufacturer, the operation's diving safety manual, and the applicable regulations govern.

Volume arithmetic on the chamber's own dimensions and the operation's inventory; no treatment table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: chamber_volume_cuft, treatment_pressure_psig, ventilation_acfm_per_occupant, occupant_count, treatment_minutes, air_inventory_cuft, oxygen_acfm_per_occupant, oxygen_minutes, treatment_ata, pressurize_cuft, ventilation_cfm_free, ventilation_cuft, total_air_cuft, ventilation_share_pct, oxygen_required_cuft, longest_treatment_min

• Ventilation dominates, not pressurization a supply sized on pressurization alone covers a fraction of the needchamber operations
• Size against the LONGEST table plus its extensions, not the shortesttreatment table practice
• Oxygen is its own inventory running out of it ends the treatmentchamber operations