The exact cause of the fire in the Apollo 1 command module is still debated, but it is believed to have been caused by a spark from faulty wiring that ignited the highly flammable materials inside the module, such as the nylon netting and Velcro used to secure equipment.
The Apollo 1 fire had a significant impact on the Apollo program, causing a delay of almost two years while safety measures were implemented and the command module design was revised. It also led to changes in the culture and procedures of NASA to prioritize safety over schedule and cost.
The pressure inside the Apollo 1 command module was approximately 16 pounds per square inch (psi) during the fire. This was higher than the normal operating pressure of 5 psi, which was necessary to simulate the pressure of the Earth's atmosphere.
The pressure inside the Apollo 1 command module was tested using a pressurization system that pumped nitrogen gas into the module. This system was then used to maintain the pressure during the mission and to purge the module of any harmful gases before re-entry into Earth's atmosphere.
Yes, the design of the Apollo 1 command module was extensively revised after the fire to improve safety. Changes included replacing flammable materials with fire-resistant ones, redesigning the hatch for quick and easy opening, and adding escape routes and equipment for the astronauts. These changes were also applied to the later Apollo missions and continue to be used in spacecraft design today.