Any person conducting aircraft servicing, maintenance, or testing of the fuel system using the air ventilation procedures, shall reduce the fuel tank atmosphere to below 20% of the lower flammable limit of the fuel vapors. Air ventilation, as used herein, means to pass undiluted air (air not containing flammable vapors) through an aircraft fuel tank to render the atmosphere of the tank below the lower flammable limit of the fuel vapors involved. Before any inspection or work is performed, tests by a qualified person shall be conducted to determine that the presence of flammable vapors in or around the fuel tank does not constitute a fire or explosion hazard. This condition shall be maintained throughout the period of inspection or work.