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Issue date: 17 November 2006
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come into contact with
the face mask double reflex seal, in a clean shaven condition and free
from beard, stubble and sideburn hair.
7.10
The HSE advise, and past fire brigade experience shows, that sweating can cause face masks to
slip. This increases the chance that the mask will come into contact with facial hair etc.
Facial
hair is an avoidable hazard
; all firefighters trained in BA must remain clean shaven. Hair, (facial
or head) or any adornment in contact with the face mask seal has the potential to impair the
efficiency of the seal and compromise the respiratory protection of the wearer, and
must be
removed
.
7.11
Cosmetics/sun tan creams must not come into contact with the face mask rubber seal as this
degrades the rubber and may affect the quality of the seal. See
uniform and personal appearance (section 8) for further details.
8
Lung demand valve (LDV)
Operation of the LDV
8.1
Before opening the cylinder valve, the first breath
mechanism must be operated. To do this press the
green first breath button on the top of the LDV which
will lift and lock the main pivot lever and diaphragm
(see image right).
Warning:
do not
try to operate the first breath
button (on top) and the ‘additional flow’ button (at
the front) simultaneously.
This will result in
damage to the LDV and may render it
inoperative.
8.2
The conical compression spring in the main chamber of the balanced piston unit, acts against the
piston flange resulting in the piston cone being pressed against the sealing rim of the piston
housing – sealing ‘off’ the outlet of the balanced piston unit.
8.3
On opening the cylinder valve, medium pressure air flows from the reducer, through the medium
pressure hose of the LDV, into the air transfer block then into the main chamber of the balanced
piston unit.
8.4
When the wearer begins to inhale a negative pressure is created inside the mask and LDV. Due
to the negative pressure, the ambient air pressure acts against the diaphragm.
First breath
button
Additional flow
button
