How long would it take to ignite a thermally thin piece of wool fabric that is 2 mm thick, has a density of 50 kg/m3, a specific heat of 0.84 kJ/kgK, and a thermal conductivity of 0.04 W/mK if it is being exposed to a heat flux of 8 kW/m2? The ambient temperature of the wool fabric was 18 Celsius and has an ignition temperature of 250 Celsius.