The SIGMA 40-II Hyperbaric System provides hyperbaric oxygen therapy for two patients. The maximum operating pressure is 30 psig (3 ATA). The system is pressurized with breathing quality air. Patients are seated in comfortable, adjustable, fully padded treatment chairs. Patients breathe pure oxygen through a built in breathing system (BIBS), using “Duke” style hoods. The SIGMA 40-II pressure vessel is constructed of aluminum end heads and includes a quick opening door assembly. A seamless clear acrylic plastic cylinder is held in sealed position between the end heads by four steel tie-rods. Safety interlocks prevent the chamber from being pressurized until the door is properly secured, and also prevents the door from being opened while the vessel is pressurized.