| 摘要 |
A respirator (1) comprises an inner, oronasal, mask (2) enclosed within an outer, face sealing, mask (3) so as to define a cavity (4) therewith, a scre w- threaded air inlet (5) for conducting inhaling air to the interior of the inner mask (2), a filter canister (7) for filtering the inhaling air, and an air outlet (8) for conducting exhaled air from the interior (6) of the inner mask (2). In normal operation, air is inhaled and exhaled solely through the inner mask (2) and so substantially no air pressure differential exists between the ambient atmosphere (9) and the cavity (4) which will allow ambie nt air to enter the cavity.
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