[ceejayoz]

I think that vastly underestimates the dependency tree in modern society. Storing hydrogen in useful quantities is tough, requiring fairly sophisticated metallurgy and cryogenics.

Finding out we've got a hard to replace left-pad module somewhere far up the tech tree wouldn't be fun.

[Robotbeat]

The dependency tree of 19th Century or early 20th century society is a lot more straightforward, however.

And no, you don't need such sophistication for storing useful amounts of hydrogen. Storing large amounts of hydrogen (in this case, also mixed with poisonous CO) was solved in the beginning of the 19th Century (well, late 18th century) in Britain and Germany by using very large near-atmospheric storage vessels called Gas Holders: https://en.wikipedia.org/wiki/Gas_holder

Salt caverns can also be used for greater volumes, i.e. for seasonal storage, as are already used for hydrogen storage in a few places in the US and elsewhere. https://en.wikipedia.org/wiki/Underground_hydrogen_storage

[Retric]

Except the Iron Age started around 2000 BC, so the world would largely be without iron for a very long time.

[mcguire]

That gas holder article says they contained methane or coal gas. Methane's density is 0.657 kg/m³; hydrogen's is 0.08375 kg/m³.

[Robotbeat]

Coal gas is a mix that (by energy) is about half hydrogen, as I said. And hydrogen gas a specific energy of 142MJ/kg vs 55.5MJ/kg for methane.