avoid carrying debris into the cabin. The suit is worn during launch and re-entry of the Soyuz spacecraft—the gloves are attached and the visor is sealed at these times. In an emergency, the suit pressure is usually maintained at 400 hPa (0.39 atm, 5.8 psi) above the ambient by the pressure relief valve. However, the suits only have a rudimentary pressure relief layer so they tend to balloon when inflated. Movement of the wearer becomes restricted, although it is still possible to function inside the capsule. If more than limited movement is required, the pressure relief valve may be adjusted to a lower setting of 270 hPa (0.26 atm, 3.9 psi). Pure oxygen at this pressure will support life, but the setting is only intended for use in extreme emergencies; the risk of decompression sickness becomes significant if the wearer spends more than 15 minutes at the lower pressure setting. The maximum length of time the suits may be used in a vacuum is 125 minutes. The time is limited because the oxygen flow to the suit is enough for life support, but insufficient to carry away the cosmonaut's body heat and longer use of the suit risks heat exhaustion. If the capsule becomes depressurised, either accidentally or deliberately to extinguish a fire, it must land within that time. History Pressure suits were worn on the Vostok space missions, but when the Soyuz spacecraft was being developed in the mid-1960s, the controversial decision was taken by its designers, OKB-1, not to use them on the new spacecraft. Some of the early Soyuz flights carried Yastreb space suits but these were only for space walks and were only worn in orbit. On June 30, 1971, the crew of Soyuz 11 died when their spacecraft depressurised during re-entry. One of the recommendations of the investigating government commission was that pressure suits should be worn by future crews during critical phases of their mission - launch, docking and landing. NPP Zvezda was given the task of providing the suits. They rejected the use of existing Soviet space suits and chose to base a new suit on the existing Sokol aviation pressure suit. The main modification was the replacement of the Sokol suit's hard helmet. Other features of the aviation suit that were considered unnecessary were removed to save weight. At the same time, a life support system was developed in co-operation with OKB-1.