The Air Force has launched a testing program to determine if the natural radioactive gas radon is posing a health threat at its bases. The service said it would begin an initial screening for the gas early next month at Air Force bases around the world. Thirty buildings will be selected at random for testing at each of the 136 Air Force bases where military housing is maintained, the service said. Child-care centers, schools and family housing will also be selected at random along with barracks and dormitories. If any building at a base is found to have radon levels exceeding federal guidelines, all the buildings at that facility will be tested, the Air Force said. Results from the screening are expected in May. Radon is a colorless, odorless natural product of decaying uranium in the soil. Medical research has indicated that exposure to high levels of radon may increase the risk of lung cancer.