The WB-57 is capable of flying at altitudes well over 60,000 feet. Twelve miles high, the environment is very inhospitable to people. In fact, there is less than 1 psi of atmospheric pressure and temperatures will approach -70° F. For these reasons, flight rules mandate that for flight above 50,000 feet, all crewmembers must wear a full pressure suit. If the cabin were to depressurize, or the crew was forced to eject, it would be the only means of survival.
Above 10,000 feet, atmospheric pressure becomes low enough that without breathing 100% oxygen, the average person will become hypoxic (an oxygen deprived state) and can eventually lose consciousness.
Photo of a Pressure suit
As altitude increases, the Time of Useful Consciousness (TUC) becomes shorter. The TUC at 60,000 feet is only 9 - 12 seconds.
The TUC can be pushed much higher if 100% oxygen is breathed. At a height of 35,000 feet, the pressure is approximately 20% that of sea level, and since oxygen is approximately 20% of air, a person at this altitude breathing pure oxygen will receive a sea level equivalent amount of oxygen. At heights above 50,000 feet, even with 100% oxygen, a person will quickly become hypoxic, because the ambient pressure is so low that the lungs will not absorb the oxygen. It is at this altitude that a pressurized flight suit must be worn. Any altitude above 50,000 ft. is labeled as "space equivalent zone".
The pressure suit used on the WB-57 weighs 31 lbs and is very similar to the suit worn by space shuttle crewmembers during launch and entry. It is designed to pressurize only if cabin pressure is lost at an altitude above 35,000 feet. The suits have two back up systems in case the primary system fails. The secondary system will activate when at 37,000 feet. Both of these two systems will deactivate when the lower threshold is reached. There is also an emergency system that if activated at 39,000 feet will not depressurize until it is done manually.