Aircraft Flight Operation Regulations Article 255

A flight to be operated above pressure (altitudes) 700hpa (10,000ft) in personnel on board compartments shall not be commenced unless sufficient stored breathing oxygen is carried to supply.An aircraft intended to he operated at flight altitude above 10,000ft shall maintain pressure (altitude) in personnel on board compartments lower than 700hpa (10,000ft) or be equipped with oxygen storage and dispensing apparatus capable of storing and dispensing the oxygen supplies required in Article 225.Pressurized aircraft intended to operate above pressure (altitude) 376hpa (25,000ft) shall be equipped with a device to provide positive warning to the pilot of any dangerous loss of pressurization.Aircraft for which the certificate of airworthiness was first issued on or after 9 Nov 1998, and which are intended to be operated at flight altitudes higher than 25,000ft, or which, if operated at flight altitudes of 25,000ft or lower, cannot descend safely within four minutes to a flight altitude of 13,000ft, shall be provided with automatically deployable oxygen equipment and oxygen supplies in compliance with Article 225.The total number of oxygen dispensing units shall exceed the number of passenger and cabin crew seats by at least 10 per cent.