Comment by jofer

Yeah, ammonia leaks are much more nasty than methane or hydrogen leaks. Methane, especially in LNG form, is quite safe compared to ammonia. LPG is even more stable than LNG and requires lower pressures. With that said, hydrogen leaks are "fun" because large ones usually self ignite and burn with a hot but mostly invisible flame. But hydrogen itself isn't toxic. Similarly, methane and propane aren't directly toxic.

Basically, an ammonia leak will kill you. By itself. The others are only a problem if they're the right concentrations to ignite. That's a relatively high concentration and a larger leak. Much smaller leaks of ammonia are deadly.

It's still a good solution for some things, but it's a bad solution for consumer vehicles like cars for that reason.