Leaking fuel, hydraulic, deicing, or lubricating fluids are potential sources of fire in an aircraft and must be identified and corrected during inspection. Even small pressure leaks are hazardous because they can quickly create an explosive atmosphere.
Fuel tank installations should be inspected carefully for signs of external leakage. In aircraft with integral fuel tanks, evidence of the leak may appear some distance from the actual point where the fuel is escaping. Drain lines, fittings, flexible hoses, and hose connections should also be examined for seepage, staining, looseness, chafing, cracking, or deterioration. Hydraulic fluids, particularly flammable types, must not be allowed to accumulate within the aircraft structure.
Soundproofing, insulation, and lagging materials can become highly flammable when saturated with oil or other combustible fluids. Any leakage or spillage of flammable fluid near a combustion heater is especially dangerous because vapors may be drawn into the heater and pass over the hot combustion chamber.
Electrical wiring and equipment should also be inspected for loose connections, damaged insulation, arcing, or overheating, particularly in areas where fuel or hydraulic vapors may be present. Adequate ventilation must always be maintained when working around flammable vapors to prevent the buildup of explosive concentrations.
Oxygen system components must be kept completely free of oil, grease, and other petroleum products. These materials can ignite spontaneously when exposed to oxygen under pressure. Only approved oxygen-compatible cleaning agents and materials should be used when cleaning or servicing oxygen system equipment. Oxygen servicing cylinders should be clearly marked and separated so they cannot be mistaken for air or nitrogen cylinders, since maintenance errors of this type have resulted in serious explosions.