At 18,300 metres (60,000 ft), Concord’s cabin altitude pressure was maintaned at an equivalent to 1,700 metres (5,500ft), Considerably below that of a subsonic aircraft.
Airliner cabins are usually pressurised to 6-8,000 ft (1,800-2,400 m) elevation while the aircraft flies much higher. Concorde’s pressurisation was set to an altitude at the lower end of this range, 6000 feet. Some passengers can have difficulty even with that pressurisation. A sudden reduction in cabin pressure is hazardous to all passengers and crew. Concorde’s maximum cruising altitude was 60,000 ft (18,000 m) (though the typical altitude reached between London and New York was about 56,000 ft (17,000 m)); subsonic airliners typically cruise below 40,000 ft (12,000 m). Above 50,000 ft (15,000 m), the lack of oxygen would limit consciousness in even a conditioned athlete to no more than 10-15 seconds. A cabin breach could even reduce air pressure to below the ambient pressure outside the aircraft due to the Venturi effect, as the air is sucked out through an opening. At Concorde’s altitude, the air density is very low; a breach of cabin integrity would result in a loss of pressure severe enough so that the plastic emergency oxygen masks installed on other passenger jets would not be effective, and passengers would quickly suffer from hypoxia despite quickly donning them. Concorde, therefore, was equipped with smaller windows to reduce the rate of loss in the event of a breach, a reserve air supply system to augment cabin air pressure, and a rapid descent procedure to bring the aircraft to a safe altitude. The FAA enforces minimum emergency descent rates for aircraft and made note of Concorde’s higher operating altitude, concluding that the best response to a loss of pressure would be a rapid descent. Pilots had access to Continuous Positive Airway Pressure which used masks that forced oxygen at higher pressure into the crew’s lungs. Had access to CPAP (Continuous Positive Airway Pressure) which used masks that forced oxygen at higher pressure into the crew’s lungs
The BAe Systems air conditioning system, comprised of four independent subsystems, with Hamilton Standard heat exchangers. The pressure differential was 0.74 bars (10.7 lb/sq in). In each subsystem the air passes through a primary ram-air heat exchanger to an air cycle cold-air unit and then through secondary air/air and air/fuel heat exchangers. The air was then mixed with hot air and fed to the cabins, flight deck, baggage holds, landing gear, equipment and radar bays.