"Clear View Window" restrictions
Regarding the restrictions against opening the "Clear View Window" --
Rummaging around out there on the coffee table, I did locate that issue of _Air Line Pilot_, of July 1948, pg 7:
"In lieu of adequate masks and until such are provided, it is advisable to have the fire axe handy to punch a hole in the forward windshield to provide sufficient oxygen. Do not open the clear view window as you will suck more CO2 into your face. Remember that punching a hole in the forward shield should be a last resort...."
[There had been several inflight fire mishaps, which led to installation of extinguishers; these engineered safety features (the CO2 gas) proved fatal in later use, where pilots did not yet have O2 masks.]