Aircraft Flight Operation Regulations Article 225

A flight to be operated at flight altitudes at which the atmospheric pressure in personnel compartments will be less than 10 000 feet (Absolute pressure 700 hPa) shall not be commenced unless sufficient stored breathing oxygen is carried to supply:1. All crew members and 10 per cent of the passengers for any period in excess of 30 minutes that the pressure in compartments occupied by them will be between 10 000 feet and 13 000 feet (Absolute pressure 700 hPa and 620 hPa); and2. The crew and passengers for any period that the atmospheric pressure in compartments occupied by them will be less than 25000 feet (Absolute pressure 376 hPa).A flight to be operated with a pressurized aircraft shall not be commenced unless a sufficient quantity of stored breathing oxygen is carried to supply all the crew members and passengers, as is appropriate to the circumstances of the flight being undertaken.1. In the event of loss of pressurization, for any period that the atmospheric pressure in any compartment occupied by them would be less than 10 000 feet.2. When an aircraft is operated at flight altitudes at which the atmospheric pressure is less than 25 000 feet there shall be no less than a 10-minute supply for the occupants of the passenger compartment.3. When an aircraft is operated at flight altitudes at which the atmospheric pressure is less than 25 000 feet, or which, if operated at flight altitudes at which the atmospheric pressure is more than 25 000 feet and cannot descend safely within four minutes to a flight altitude at which the atmospheric pressure is equal to 13 000 feet.All flight crew members, when engaged in performing duties essential to the safe operation of an aircraft in flight, shall use breathing oxygen continuously whenever the circumstances prevail for which its supply has been required in the preceding 2 paragraphs.