The government ordered safety inspections of hundreds of railroad tank cars that carry volatile or otherwise hazardous materials. The Federal Railroad Administration said the compressed gases often shipped in the 30-year-old "dual-diameter" pressure tank cars might explode if a car leaks, and the resulting vapors "could be immediately harmful to persons in the area." The National Transportation Safety Board recommended the inspections after a tank car of liquefied propane derailed near Dragon, Miss., in January. Witnesses said a white vapor cloud enveloped the area, then burst into flames. Investigators said they had found a 12-inch crack in the derailed car and cracks ranging from two inches to 30 inches in three similar cars.