English: 17 October 1913: On the morning of a scheduled test flight at Johannisthal, an airfield south east of Berlin, Germany, L2, the second rigid airship built for the Kaiserliche Marine (Imperial German Navy) by Luftschiffbau Zeppelin at Friedrichshafen, was delayed by problems with the engines. The morning sun heated the hydrogen contained in the airship’s gas bags, causing the gas to expand and increasing the buoyancy.

Once released, L2 rapidly rose to approximately 2,000 feet (610 meters). The hydrogen expanded even more due to decreasing atmospheric pressure. To prevent the gas bags from rupturing, the crew vented hydrogen through relief valves located along the bottom of the hull.

In this early design, the builders had placed the relief valves too close to the engine cars. Hydrogen was sucked into the engines’ intakes and detonated. L2 caught fire and a series of explosions took place as it fell to the ground.

All 28 persons on board were either killed immediately, or died of their injuries shortly thereafter.^{http://images.google.de/imgres?imgurl=https://static.thisdayinaviation.com/wp-content/uploads/tdia//2014/10/in-brand-das-luftschiff-l-2-ist-bereits-unrettbar-verloren-was-die-zuschauer-am-boden-erkennen-die-deshalb-um-ihr-leben-laufen.jpg&imgrefurl=https://www.thisdayinaviation.com/tag/l2/&h=705&w=940&tbnid=IcpaOnLN48jr9M:&tbnh=88&tbnw=117&docid=08b8FK7VoWEhZM&itg=1&usg=__GNUcsp4qq8kzFaqXoZkUE-jh0C4=&sa=X&ved=0ahUKEwi-q5e3n9XPAhVBnxQKHaGZBd4Q9QEILDAC}