Standards for firewalls may be based on their thermal response to a prescribed radiant heat flux. Consider a 0.25-m-thick concrete wall (rho= 2300 kg/m3, c= 880 J/kg·K, k= 1.4 W/m·K), which is at an initial temperature of Ti= 25°C and irradiated at one surface by lamps that provide a uniform heat flux of qs′′= 0.85·104 W/m2. The absorptivity of the surface to the irradiation is αs= 1.0. If building code requirements dictate that the temperatures of the irradiated and back surfaces must not exceed 325°C and 25°C, respectively, after 30 min of heating, will the requirements b