All fires occurring in air produce carbon dioxide. Fire involving nitrogen containing products will also generate nitrogen dioxide, a pulmonary irritant. In Fischer 344 male rats, the "LC 50" (30 minute exposure plus 14 day post-exposure observation period) for Nitrogen dioxide was 200 ppm (with 95 percent confidence limits of 43 to 51 percent); whereas, the "LC 50" for Nitrogen dioxide in the presence of 5 percent Carbon dioxide was 90 ppm (with 90 percent confidence limits ranging from 70-120 ppm). ... The time of death was concentration dependent when both gases were present. At death, evidence of hemorrage and extensive edema was observed in the lungs. The mean lung wet weigh/body weight ratio from rats exposed to 200 ppm Nitrogen dioxide with and without 5 percent Carbon dioxide was 3-4 times that of non-exposed rats. More edema was noted with Nitrogen dioxide and Carbon dioxide than with Nitrogen dioxide alone.