A conduit (12,152, 400) for delivering a supply of gas (408) under a positive pressure includes a conduit wall (402) having a first conduit end (28, 404) and a second conduit end (40, 406). The first conduit end (28, 404) is adapted to be attached to the supply of gas (408). The conduit wall (402) is deformable between (1) an open condition in which the conduit wall (402) defines a conduit passage (410) along which the supply of gas can travel between the first conduit end (28, 404) to the second conduit end (40, 406), and (2) a collapsed condition in which the conduit wall (402) substantially collapses the conduit passage (410).
