had recommended changing the design to an outward-opening hatch, and this was already slated for inclusion in the Block II command module design. According to Donald K. Slayton's testimony before the House investigation of the accident, this was based on ease of exit for spacewalks and at the end of flight, rather than for emergency exit. Emergency preparedness The board noted that the test planners had failed to identify the test as hazardous; emergency equipment (such as gas masks) were inadequate to handle this type of fire; that fire, rescue, and medical teams were not in attendance; and that the spacecraft work and access areas contained many hindrances to emergency response such as steps, sliding doors, and sharp turns. Choice of pure oxygen atmosphere When designing the Mercury spacecraft, NASA had considered using a nitrogen/oxygen mixture to reduce the fire risk near launch, but rejected it based on a number of considerations. First, a pure oxygen atmosphere is comfortably breathable by humans at , greatly reducing the pressure load on the spacecraft in the vacuum of space. Second, nitrogen used with the in-flight pressure reduction carried the risk of decompression sickness (known as "the bends"). But the decision to eliminate the use of any gas but oxygen was crystalized when a serious accident occurred on April 21, 1960, in which McDonnell Aircraft test pilot G. B. North passed out and was seriously injured when testing a Mercury cabin / spacesuit atmosphere system in a vacuum chamber. The problem was found to be nitrogen-rich (oxygen-poor) air leaking from the cabin into his spacesuit feed. North American Aviation had suggested using an oxygen/nitrogen mixture for Apollo, but NASA overruled this. The pure oxygen design was judged to be safer, less complicated, and lighter in weight. In his monograph Project Apollo: The Tough Decisions, Deputy Administrator Seamans wrote that NASA's worst mistake in engineering judgment was not running a fire test on the command module before the plugs-out test. In the first episode of the 2009 BBC documentary series NASA: Triumph and Tragedy, Jim McDivitt said that NASA had no idea how a 100% oxygen atmosphere would influence burning. Similar remarks by other astronauts were expressed in the 2007 documentary film In the Shadow of the Moon. Other oxygen incidents Several fires in high-oxygen test environments had occurred before the Apollo fire. In 1962, USAF Colonel B. Dean Smith was conducting a test