North American had originally suggested the hatch open outward and use explosive bolts to blow the hatch in case of emergency, as had been done in Project Mercury. NASA did not agree, arguing the hatch could accidentally open, as it had on Grissom's "Liberty Bell 7" flight, so the Manned Spacecraft Center designers rejected the explosive design in favor of a mechanically operated one for the Gemini and Apollo programs. Before the fire, the Apollo astronauts 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.