Early Stage of Elevated Fires in an Aircraft Cargo Compartment: A Full Scale Experimental Investigation

The objective of the present study is to evaluate the elevated fires using the metrics of smoke distribution and changes in fire signals at the early stage, which affect activation of fire detectors. Most previous works on elevated fires in compartments are mainly concerned with physical phenomena of fully-developed fires. However, fire signals at initial 60 s are key parameters for aircraft cargo fire detection. A series of elevated fires were conducted in a simulated Boeing 737-700 forward cargo compartment. The fuel mass loss rate, the vertical and ceiling temperature, gas concentrations and relative humidity (RH) were measured. Results show that the smoke layer interface remains constant for various fuel pan elevation heights and no clear smoke stratification phenomenon is observed during the early stage, nevertheless, the first indication of smoke has been raised. The ceiling temperature rise is attenuated at different rates for various elevations with an exponential model proposed in ceiling temperature distributions for early stage fires. 60 s after ignition of the elevated fires, compared to non-elevated fires, CO/CO2 concentrations increase by at least 3.73/1.49 times and O-2 concentration decreases by 2.5 times. The RH increases at the early stage. These experimental results can be used to inform the selection of optimum sensors, to develop appropriate detection algorithms and to optimize the number and location of fire detectors.