Meh, we could use hydrogen if we really wanted to. If you separate the lift from the people/propulsion there is little chance of a strongly rising gas leak caus

Meh, we could use hydrogen if we really wanted to. If you separate the lift from the people/propulsion there is little chance of a strongly rising gas leak causing a fire. Heck, you can even do electronics in an explosive hydrogen atmosphere (I've personally done it). It just takes a lot of care and as a result is expensive to design. What you can't do is have random people inside the outer envelope that also contains the gas bags. Anything that is going to be light enough to fly is going to leak a lot of hydrogen.