UAL2012 Oxygen Masks Deploy Descending into KDEN

[RonR]

On May 17, UAL2012 was descending into KDEN when the flight crew declared an emergency.  They told ATC that their oxygen masks had deployed but the exact reason for the deployment was not mentioned in the attached audio.  The deployment occurred while they were still taking to Denver Center; no audio is available from that ZDV sector.  The aircraft landed safely a short time later.

[KB4TEZ]

was able to pick out the pieces of the emergency declared, pressurization issues.
and that same flight back on 5/14 had diverted to Albuquerque.

[RonR]

Well, yes, obviously pressurization issues, just nothing was mentioned as to what might have caused it (cockpit warning indication, etc.)