(1) Inadequate supply for the mission. The low pressure oxygen system
in the B-17 and B-24 is fully charged to a capacity of 450 pounds
per square inch. This supply should last 7 to 9 hours, depending
on activity of the crew members (Auto-Mix "ON").
(2) Oxygen supply exhausted by leaks in oxygen lines or cylinders.
(3) Flyer getting insufficient oxygen:
(a) Attempts to do excessively hard work.
(b) Mask leak: Improper fit; frozen exhaust valve; holes in mask
or hose; growth of stubby beard.
(c) Leak around gasket between mask-regulator connection.
(d) Loose connections where supply hose connects to regulator.
(e) Freezing of moist oxygen at extremely low temperature.
(f) Obstruction of openings in regulator.
(g) Hole in rubber diaphragm in regulator.
(4) Breathing too deeply may produce a partial vacuum inside mask
causing air to leak in from bottom or sides. BREATHE NATURALLY.
5 Don't expect to get oxygen from an empty walk-around bottle.
If not fully charged, the bottle may last only a minute or two.
(6) Improper use of walk-around equipment.