Just as an add on...
Years back at a former employer, we almost lost a 727 over this. I can’t recall the specifics of how they found themselves in the situation, but somewhere in the upper 20’s, the engineer went to manually close the outflow valve and moved the switch in the opposite direction needed. This was because the aircraft he was most familiar with (C-141) worked opposite of the B727. In the heat of battle, he reverted back to his primal training. The cabin dumped. The captain, who was a heavy smoker, immediately lost consciousness. The engineer, who didn’t don his mask because he was too engrossed trying to figure out WTF just happened, followed several seconds later. Only the FO, who heard the altitude warning horn go off and thought “Oh shit...this is bad. I better get my mask on ASAP!” Remained conscious. He did his job and immediately brought the airplane down into a livable atmosphere. There were no serious injuries and the plane diverted. The owner of the company, a pilot himself, took that kid and his wife out to dinner, sent them all to Disney for a week free, and gave him an aircraft model and plaque in gratitude. He had been off IOE for a month, and the biggest plane he had flown prior was a DC-3.
I believe it’s an FAA requirement now for Pt141 schools to employ and altitude chamber in their trading curriculum. I know both my boys did it. Both of them were pretty astonished at how quickly they became debilitated..