sentences:  Emergency oxygen system
  
  Aircraft emergency oxygen systems or air masks are emergency equipment fitted to pressurized commercial aircraft, intended for use when the cabin pressurisation system has failed and the cabin altitude has climbed above a safe level.It consists of a number of individual yellow oxygen masks stored in compartments near passenger seats and near areas like lavatories and galleys, and an oxygen source, like a centralized gaseous cylinder or decentralized chemical oxygen generator.