The July 1994 incident at Harpers Ferry - what is the deep water black out while switching from bottom mix to air??
Seems to be more about breathing a dense gas and CO2. This has some info on it:
http://archive.rubicon-foundation.o.../123456789/6311/SPUMS_V26N3_14.pdf?sequence=1
It's from the 90s though, maybe someone has something more recent.