Accidental combustion events in fuel tanks and flammable leakage zone is a major concerns in aviation safety. The present study examines the possibility of inerting flammable mixtures using a long duration thermal process close to but below the auto-ignition temperature. Experiments were performed in a 1.14 L cylindrical cell made of stainless steel. A Mid-IR FTIR spectrometer was employed to monitor the gas-phase composition. Experiments were performed for n-hexane-O2 mixtures diluted with 89% and 78% nitrogen and Φ=0.67-1.35. The temperature and pressure were T=420-500 K and P=37-147 kPa. Experiments were performed over 7200 s. At low temperature, the chemical activity is characterized by a slow and constant reaction rate. At high temperature, the reaction proceeds in two-phases: 1) rapid production of CO2, CO and carbonyls followed by 2) a period of slower production of CO2 and H2O. The chemical activity in stoichiometric n-hexane-air mixtures was also monitored for up 4000 s using a He-Ne laser. At the end of the thermal treament, a glow plug was turned on to check the flammability of the mixtures. In all cases, ignition was observed.