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When recently discussing with others how young we'd first read stories with apocalyptic themes, I was reminded of a story I'd found in a middle-school library, circa 1984-1986. The protagonist was a boy or young man in a world that was about to end. I don't recall the reason, but either their looming demise seemed not to be general knowledge in his world, or they didn't believe there was any hope of avoiding it.
He encountered members of a secret group planning to survive/escape by recruiting people of every skill and talent necessary to repopulate the world (don't think it was a different planet) without sacrificing accumulated technology/knowledge. They told him about a secret (underground?) place to which the chosen few would be summoned at the appropriate time, where they could safely hide before emerging to start the world over. Since I can't recall his skills, I'm not actually certain whether he'd been selected himself or was so young he was merely family of someone who had been.
To prevent spies or those not chosen from discovering or stampeding to the protected place, there was some sort of antechamber/elevator which could destroy people with some sort of (green light?) radiation or gas--unless you wore a magic ring (or some other amulet/device). Near the end of the story, a bad guy chases our hero into the chamber and is indeed vaporized.
I recall this book's plot not because it was any good (I remember thinking much of it cheesy even at the time), but because I read it at exactly the time in my life where I was ready to ponder all the fascinating what-ifs surrounding the apocalyptic genre. Been hooked on scifi/fantasy ever since, and later studied engineering partly due to not wanting to be "that person" who knew nothing useful should the world need a fresh start. ;)
Can anyone point me to the title/author? Thanks in advance!