| 摘要 |
The invention relates to a safety helmet, including an isolated volume to which the wearer's breathing ducts open and two independent means for supplying breathable air to the isolated volume. In one described embodiment a first means supplies air from a pressure air reservoir (29) through an air supply demand valve (28) to said isolated volume (V1) and, when operational, the demand valve (28) maintains the isolated volume (V1) at a pressure higher than the surrounding atmosphere. The second means for supplying breathable air to said isolated volume includes a filter arrangement (32) and duct means (33, 34, 35) for ducting filtered air to said isolated volume. The helmet further includes a control valve means (39), arranged to close the isolated volume (V1) from said second means when the first means is supplying air to said isolated volume (V1), and manually actuable valve means (31) for selectively connecting and disconnecting the supply of air from reservoir (29) to demand valve (28). |
