Investigation of the effect of low pressure on fire hazard in cargo compartment

Highlights: • Low air pressure elevates the flame height and high-temperature region. • Fire hazard is differences for liquid and solid fire under low air pressure. • Depressurization causes the cargo liners burn-through more easily. • Smoldering induced by the depressurization could lead to flashover. -- Abstract: In-flight cargo fires are fatal threats to freighter aircraft, and depressurization is one of the main measures for fire suppression. To explore the effects of low pressure on in-flight fire and accurately assess the fire hazard during this emergency situation, liquid pool and cardboard box fire tests were conducted. Depressurization could suppress the cargo fire by reducing the mass burning rate and radiant heat flux but could not put out the fire. For liquid fires, depressurization increases the flame height and elevates the high-temperature region of the flame, resulting in cargo liner burn-through more easily. Depressurization could weaken the burning of the solid fire and eliminate the visible flame but could not eliminate smoldering. Smoldering causes the accumulation of smoke containing high carbon particles and flammable gas and increases the possibility of flashover. For solid fires, the greatest danger exists in the flashover caused by pressure recovery during the landing. Combustion characteristic of the loads and other synergetic fire control measures should be considered simultaneously with the depressurization fire suppression.