However, for the low oxygen levels to be the result of displacement of air, extremely large volumes of carbon dioxide would have been required. For instance, to decrease oxygen volumetric concentration to 10% would require a carbon dioxide content of about 52% or 520,000 ppm. By contrast, to lower oxygen concentration from 20.9% to 10% through replacement with carbon dioxide would theoretically require a carbon dioxide concentration of only 109,000 ppm (10.9%)