(a) Be sure the regulator hose clip or the clip on the walk-around
bottle is clipped high enough on your clothing to remove all
tension from mask hose--otherwise the mask will be pulled down
on the face and will leak outside air.
(b) Above 25,000 feet with the temperature 20 degrees and lower, the
tissues of the face contract and the rubber mask loses its
pliability. Under these conditions, the mask tends to fall away
from the face and it becomes necessary to SHORTEN THE UPPER
SUSPENSION STRAPS. On returning to warmer altitudes, these must
be loosened again to avoid discomfort from a too tightly fitting
mask. (Applies chiefly to gunners).
(3) Excessive beard stubble will hold the mask away from the face and
cause leak around the jaws.
(4) See page 35 for care of mask.
(5) TESTING FOR LEAKS -- Holding the thumb over the end of the mask tube
(rapid disconnect) and inhaling GENTLY should cause the mask to collapse
on the face. The most common place for a leak is alongside the bridge of
the nose. The actual site of leak is determined by putting finger-point
pressure beside the nose and over the cheek bones, one point at a time.
The nose wire is then re-adjusted to cause pressure at this point. Be
sure the mask is high enough on the face and on the bridge of the nose.
If the seal is still below the boney portion of the nose try the next
largest size mask.
(6) "SNIFF-TESTER" -- An effective "sniff-tester" for detecting small
leaks can be obtained as follows: Obtain one of the commercial nasal
inhalers - Benzedrine, Vick's, Penetro (or metal tube of comparable
size). Cut off the end ordinarily inserted into the nose flush with the
barrel of the container, and remove contents. Fit barrel with an
airtight cork stopper. Straighten a paper clip or take a piece of wire
of similar gage, cut to 2½ inch length, and drive one end firmly into
lower side of cork stopper. Fashion other end of wire into a 1/4 inch
fish hook bend. Make a ball of cotton or tightly wrapped gauze, ½ inch
in diameter, and attach to bent end of wire. Soak the cotton or gauze,
in oil of peppermint or oil of cloves (obtained from squadron dentist or
flight surgeon) and fit cork stopper, carrying the "sniff-tester"
tightly into metal container. To "sniff-test", remove the stopper and
hold the cotton plug on both sides of the nose at the top of the mask
(eyes closed). Inhale gently with the mask hose blocked. A leak is
present if the contents of the "sniff-tester" is detected. Rough as this
test seems, it is very sensitive.
NOTE: The "sniff-tester" is also effective in testing the DEMAND
REGULATOR for leaks. Put on mask. Fit snugly to face. Plug into
regulator hose. Turn Auto-Mix (Air) Lever OFF. Hold sniff-tester close
to regulator diaphragm and breathe normally several times. If the
contents of the sniff-tester" are detected, the regulator has a leak.