 The plugs @-@ out test had been run to simulate the launch procedure , with the cabin pressurized with pure oxygen at the nominal launch level of 16 @.@ 7 psi ( 115 kPa ) , 2 psi ( 14 kPa ) above standard sea level atmospheric pressure . This is more than five times the 3 psi ( 21 kPa ) partial pressure of oxygen in the atmosphere , and provides an environment in which materials not normally considered highly flammable will burst into flame . 
