The Boomers kind of make it sound like it's been a few generations since they left the vault, but Chris Haverson with the Bright Brotherhood makes it sound like Vault 34 becoming an irradated hellhole happened within the last few years.

Anyone care to enlighten me?

Maybe that's exactly what happened... some people wanted to leave and left and others did not. Th porblem was over-population after-all, theywere probably grateful that some people chose to leave when they did.

Thanks I never really thought that the two events weren't connceted, but that makes sense.

Yep, Chris even says he left two years ago as in he has been with the ghouls for two years.

What happened is the Boomers were the ones who wanted to leave and they left peacefully and founded their community. Decades later more people wanted to leave but the Overseer wouldn't let them. Chris got out of the Vault from what I suspect is a secret way out. Vault such as Vault 19 and 101 have more then one way in and out. Some time in the two years since he left things went bad in the Vault and the reactor was damaged in a riot.