Editing Apollo 1 (section)

=== Command module redesign ===
After the fire, the Apollo program was grounded for review and redesign. The command module was found to be extremely hazardous and, in some instances, carelessly assembled (for example, a misplaced wrench socket was found in the cabin).<ref name="aibreport" />{{Reference page|page=5–10}}

It was decided that the remaining Block I spacecraft would be used only for uncrewed Saturn V test flights. All crewed missions would use the [[Apollo command and service module#Major differences between Block I and Block II|Block II spacecraft]], to which many command module design changes were made:
* The cabin atmosphere at launch was adjusted to 60% oxygen and 40% nitrogen at sea-level pressure: {{convert|14.7|psi|kPa|abbr=on}}. During ascent the cabin rapidly vented down to {{convert|5|psi|kPa|abbr=on}}, releasing approximately 2/3 of the gas originally present at launch. The vent then closed and the environmental control system maintained a nominal cabin pressure of {{convert|5|psi|kPa|abbr=on}} as the spacecraft continued into vacuum. The cabin was then very slowly purged (vented to space and simultaneously replaced with 100% oxygen), so the nitrogen concentration gradually fell off to zero over the next day. Although the new cabin launch atmosphere was significantly safer than 100% oxygen, it still contained almost three times the amount of oxygen present in ordinary sea-level air (20.9% oxygen). This was necessary to ensure a sufficient [[partial pressure]] of oxygen when the astronauts removed their helmets after reaching orbit. (60% of five psi is three psi, compared to 60% of {{convert|14.7|psi|kPa|abbr=on}} which is {{convert|8.8|psi|kPa|abbr=on}} at launch, and 20.9% of {{convert|14.7|psi|kPa|abbr=on}} which is {{convert|3.07|psi|kPa|abbr=on}} in sea-level air.)<ref name="chariot" />
* The environment within the astronauts' pressure suits was not changed. Because of the rapid drop in cabin (and suit) pressures during ascent, [[decompression sickness]] was likely unless the nitrogen had been purged from the astronauts' tissues before launch. They would still breathe pure oxygen, starting several hours before launch, until they removed their helmets on orbit. Avoiding the "bends" was considered worth the residual risk of an oxygen-accelerated fire within a suit.<ref name="chariot" />
* Nylon used in the [[Gemini space suit|Block I suits]] was replaced in the [[Apollo/Skylab A7L|Block II suits]] with [[Beta cloth]], a non-flammable, highly melt-resistant fabric woven from [[Glass (fiber)|fiberglass]] and coated with Teflon.<ref name="chariot">{{Cite web |last1=Brooks |first1=Courtney |last2=Grimwood |first2=James |last3=Swenson |first3=Loyd |date=1979 |title=The Slow Recovery |url=http://www.hq.nasa.gov/office/pao/History/SP-4205/ch9-4.html |access-date=May 14, 2016 |publisher=NASA}}</ref>
* Block II had already been planned to use a completely redesigned hatch which opened outward, and could be opened in less than five seconds.<ref name="chariot" /> Concerns of accidental opening were addressed by using a cartridge of pressurized nitrogen to drive the release mechanism in an emergency, instead of the [[explosive bolt]]s used on Project Mercury.
* Flammable materials in the cabin were replaced with self-extinguishing versions.
* Plumbing and wiring were covered with protective [[thermal insulation|insulation]]. Aluminum tubing was replaced with stainless steel tubing that used brazed joints when possible.<ref name="chariot" />

Thorough protocols were implemented for documenting spacecraft construction and maintenance.