Hydrogen is not toxic by inhalation, but it's a much worse explosion/fire risk.

Hydrogen is flammable when mixed with air between 4% and 75%, and it takes a minimum energy of 0.016 millijoules to ignite. Ammonia is flammable between 15% and 28% and takes 680 millijoules to ignite. It takes much more energy to ignite ammonia and there's a much narrower range of mixtures with air where it can support combustion.

https://en.wikipedia.org/wiki/Flammability_limit#Examples