Having read the comments of the National Transportation Safety Board following its 'major investigation' into the loss of the Lear Jet in 1999, in which they opined that
"Investigations of other accidents in which flight crews attempted to diagnose a pressurization problem or initiate emergency pressurization instead of immediately donning oxygen masks following a cabin altitude alert have revealed that, even with a relatively gradual rate of depressurization, pilots have rapidly lost cognitive or motor abilities to effectively troubleshoot the problem or don their masks shortly thereafter. In this accident, the flight crew's failure to obtain supplemental oxygen in time to avoid incapacitation could be explained by a delay in donning oxygen masks of only a few seconds in the case of an explosive or rapid decompression or a slightly longer delay in the case of a gradual decompression. "
1999 South Dakota Learjet crash - Wikipedia, the free encyclopedia
And the speculation here that the pilot's oxygen supply may have been compromised by airframe damage, am I to assume that there is no redundancy in the event that the primary oxygen supply is compromised?