Dr. Eckener rejected the idea that hydrogen could have been ignited by an engine backfire, postulating that the hydrogen could not have been ignited by any exhaust because the temperature is too low to ignite the hydrogen. The ignition temperature for hydrogen is , but the sparks from the exhaust only reach . The Zeppelin Company also carried out extensive tests and hydrogen had never ignited. Additionally, the fire was first seen at the top of the airship, not near the bottom of the hull.