In addition to complying with the requirements of section 4.6 or 4.7, as
applicable, a lifeboat with a self-contained air support system shall
be so arranged that, when proceeding with all entrances and openings
closed, the air in the lifeboat remains safe and breathable and the
engine runs normally for a period of not less than 10 min. During
this period the atmospheric pressure inside the lifeboat shall never
fall below the outside atmospheric pressure nor shall it exceed it
by more than 20 hPa. The system shall have visual indicators to indicate
the pressure of the air supply at all times.