opening airtight hard hatch, and an outwardly hinged thermal cover. The inner airtight hatch gets stowed at the end of the crew lock to allow ingress and egress. In the crew lock is the Umbilical Interface Assembly, able to support two US suits, or two Orlan-M suits, or one of each. Camp-out procedure Quest provides an environment where astronauts can "camp out" before a spacewalk in a reduced-nitrogen atmosphere to purge nitrogen from their bloodstream and avoid decompression sickness in the low-pressure () pure-oxygen atmosphere of the spacesuit. In April 2006, Expedition 12 Commander Bill McArthur and Expedition 13 flight engineer Jeffrey Williams tested this new method of preparing for spacewalks by spending the night in the Quest Airlock. In the chamber, the pressure was reduced from the normal . Four hours into the Expedition 13 crew's sleep period, an error tone prompted mission controllers to cut short the activity, but the test was still deemed a success. American spacewalk activities thereafter have employed the "camp-out" pre-breathing technique. The previous method of preparing for spacewalks involved breathing pure oxygen for several hours prior to an EVA to purge the body of nitrogen. More recently astronauts have been using the In-Suit Light Exercise protocol rather than camp-out to prevent decompression sickness. High-pressure gas tanks Two oxygen and two nitrogen high-pressure gas tanks are attached externally to the equipment lock segment. These tanks (known as the High Pressure Gas Assembly.) provide a replenishable source of gas to the atmosphere control and supply system and oxygen for recharging the space suits (EMUs). Recharging the high-pressure tanks was accomplished by the Space Shuttle fleet until its retirement. When an orbiter was docked to the station's Pressurized Mating Adapters (PMA-2 or PMA-3), oxygen was routed through pressure lines from the PMAs to the Quest Airlock. The pumping of the oxygen from the docked spacecraft tanks into Quests high-pressure tank was accomplished by the Oxygen Recharge Compressor Assembly (ORCA). After the retirement of the Space Shuttle fleet, the Nitrogen Oxygen Recharge System (NORS) and spacecraft from the Commercial Crew Development program will take over this task. Construction This module was manufactured by Boeing, under contract by NASA at the Marshall Space Flight Center in 2000. It is made from aluminum and steel alloys. The crew airlock segment was derived from the Space Shuttle's external airlock. Airlock specifications Material: aluminium and steel Length: Diameter: Mass: Volume: Cost: