I think to have once read that World War I fights against Zeppelins showed that igniting the hydrogen proved to actually be quite hard. Only when they were able

I think to have once read that World War I fights against Zeppelins showed that igniting the hydrogen proved to actually be quite hard. Only when they were able to open significant holes and used special ammunition did that work. Not enough hydrogen would escape and mix with air and remain in one place to accumulate to cause an explosion. There needed to be a big hole first for enough hydrogen to mix with air, plus the spark to ignite it. That was WWI airplanes over Britain attacking Zeppelins with their machine guns. There were a lot of compartments too, it was not all one giant space of hydrogen. EDIT: I found it mentioned in https://www.military-history.org/feature/german-zeppelins-of-wwi.htm https://www.military-history.org/feature/german-zeppelins-of... > That autumn, the British pilots deployed a new weapon. No longer dependent on dropping bombs or explosive darts over the side, nor on the standard machine-gun ammunition that appeared to have no effect whatever on the giant gas-bags, the home-defence squadrons now filled their ammunition belts with a mixture of tracer and newly-designed explosive and incendiary bullets. The idea was to blow a hole in the fabric of an airship and then ignite the escaping hydrogen as it mixed with air. Of course, once successfully blown open and ignited it would go up in flames like a torch. But it wasn't quite that simple to get to that point.