To remedy the causes of the fire, changes were made in the Block II spacecraft and operational procedures, the most important of which were use of a nitrogen/oxygen mixture instead of pure oxygen before and during launch, and removal of flammable cabin and space suit materials. The Block II design already called for replacement of the Block I plug-type hatch cover with a quick-release, outward opening door. NASA discontinued the manned Block I program, using the Block I spacecraft only for unmanned Saturn V flights. Crew members would also exclusively wear modified, fire-resistant Block II space suits, and would be designated by the Block II titles, regardless of whether a LM was present on the flight or not.