[hippoman]

If oxygen masks don't deploy when cabin pressure falls enough to make the passengers unconscious, then what is their purpose? It's hard to believe they could have such a massive design fault. Is there no sensor that could detect the depressurization?

[cpncrunch]

No, the guy is just misinformed. You won't become unconscious at 12500ft. In fact it's perfectly legal to fly at 12000ft for 30 mins. Pikes Peak is 14115ft and I don't think people are all becoming unconscious up there. Also there will always be a very obvious alarm sounding when there is a depressurization. In the Helios flight they just thought the warning was something else (i.e. pilot error / incompetence).

[ev0lution]

I'm not sure about the sensitivity of pressure sensors so I can't comment on that, but in most cases where oxygen masks are required, it is rapid decompression caused by the pressurisation system failing or a physically broken part of the aircraft that has exposed the cabin to the outside atmosphere. I'm not aware of a case like this (if this person's theory is at all plausible) where depressurisation happens slowly.