Considering the rapid and intense nature of the fatal fire, the hatch to the Apollo 1 command module might seem like a pretty irrelevant thing to consider. But as it turned out, that hatch was no simple thing, and some poor design decisions might have condemned the astronauts to death. After all, if the three men had been able to quickly escape, then the tragedy would have been avoided.
The hatch was, in fact, a death trap. It consisted of multiple different parts — including an inner and outer hatch, both of which served different purposes and had to be opened using different tools. The inner hatch also opened inward, which was a problem on its own. The pressure inside the module was higher than it was outside — a good thing in space, since it helped keep the hatch closed, but a bad thing on land, because it made the door even harder to open. Engineers recommended including explosive bolts that could knock the hatch off its hinges in an emergency (exactly the kind of emergency that Apollo 1 ultimately faced), only for NASA to shoot that down.
Missions after Apollo 4 corrected both of those mistakes by introducing an easily removable unified hatch, but for the crew of Apollo 1, they had to struggle with a hatch that was destined to lead to failure. They trained at opening the hatch in 90 seconds — still a fairly long time — and even that proved impossible for the strongest of the three. Not a good sign, surely.
