A pesticide product containing active ingredient d-phenothrin is sprayed within passenger aircraft cabins on planes flying international routes to comply with world health organization’s international health regulations. An airline cabin of 30,000 ft3 containing 10000 ppm d-phenothrin is to be flushed with fresh air until the d-phenothrin concentration is reduced to 100 ppm. At that concentration of d-phenothrin the cabin is considered safe. If the flow rate of air into the cabin is 600 ft3/min for how many minutes must the cabin be flushed out? Assume that flushing operation is conducted so that the air in the cabin is well mixed.