A fireproof safe is constructed of loosely packed asbestos contained between thin sheets of stainless steel. The safe is built in the form of a cube with inside and outside dimensions of 0.5 and 1.0 m. If the safe is initially uniform in temperature at 30ºC and the outside is suddenly exposed to a convection environment at 600ºC, h = 100 W/m2 · ºC, calculate the time required for the inside temperature to reach 150ºC. Assume the inside surface is insulated, and neglect the resistance and capacitance of the stainless steel. Take the properties of asbestos as k = 0.16 W/m · ºC, α = 3.5 × 10−7 m2/s.