Hydrogen diffuses very quickly. I would imagine no issue. There could be an issue if it were to burn, then the inhaled water could linger in your system for a w

Hydrogen diffuses very quickly. I would imagine no issue. There could be an issue if it were to burn, then the inhaled water could linger in your system for a while (although water is constantly excreted too). But then the dosage is so small, and it's alpha radiation (readily absorbed by nearby water molecules). Sure you would get a better estimate by running some calculations, but I suspect the dosage even of a handful of those totally inhaled as water vapor would be sub-background. Compare it to mercury (which some years back was still in batteries), which evaporates easily when heated, stays in your body for very long times (and is cumulative), and has clear neurological impact. I wouldn't worry about even a large number of those breaking.