Due to improper ventilation of propane-powered forklifts, carbon monoxide levels in a warehouse reached 250 ppm. The warehouse is 35 x 100 feet, with 15-foot ceilings. A ceiling mounted exhaust fan can generate an airflow of 7,500 cfm. How long will it take until carbon monoxide concentrations reach 1/10 the TLV (25 ppm) and it is safe to reenter the building?

a. 21 minutes b. 32 minutes c. 122 minutes d. 72 minutes