What happened in *spoiler*?

I'm a bit confused/might not remember what the show told us that happened in Silo 17 at the end of the revolution. So if someone would enlighten me. Here is my understanding:

Head of IT knew there was a safeguard mechanism to poison the entire silo (and possibly the area outside the silo?) and went to block it. After that he told the sheriff it's safe to go outside. Sheriff told head of IT to reveal his secrets and he did. Sheriff still killed the head of IT because he didn't tell the code to the vault. Sheriff and other people went outside and "didn't die at first" according to Solo. Is that pretty much what happened?

I say "outside the silo" too because Solo said that the head of IT told the sheriff it's safe to go outside now after he blocked the pipe. Another option would be that the air outside is actually poisonous, but the safeguard would be initiated still if people escape. So the head of IT blocked the safeguard, then told the sheriff it's safe to go outside (Because the poison is no longer risk for himself if other people go outside).

also few random questions:

was it mentioned how they blocked the poison pipe?

How did Lukas know about the safeguard at the end of s2e9? The AI voice asked do you know what the safeguard is and he did know. Did the notes from Salvador Quinn or Judge Meadows mention it? Or maybe the safeguard is something that every head of IT/shadow knows (since silo 17 head of IT knew about it too)

About relics. Did the show ever mention if silo 17 had "relics" ie. material from the old world that was prohibited. I was wondering if the outlawing old stuff was something that the builders of the silos created, or if it was a law created in silo 18 at some point.