How do the oxygen masks deploy after a cabin decompression?

Question

Is there any sensor incorporated on the Passenger Service Unit that tells the masks to deploy when a cabin decompression occurs?

score 3 · Accepted Answer · answered Apr 18 '16 at 18:48

According to this Airliners.net forum post,

The masks are deployed automatically (typically when cabin altitude exceeds 14,000 feet), or can be deployed manually from the flight deck. In addition, if a passenger service unit oxygen door should fail to open, cabin crew can open the PSU door (either inserting a flat object or a special tool depending on the aircraft type) manually.

So basically, the masks are deployed automatically based on sensors, with manual deployment as a primary failsafe and physical access as a secondary failsafe.

For completeness, many types have a manual override in the cockpit should the automatic deployment fail for whatever reason. Examples can be seen in the answers to this question. — Simon, Apr 18 '16 at 20:36

How do the oxygen masks deploy after a cabin decompression?

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