Are you trying to run it in emunand, or in sysnand with all the relevant signature patches?
If you were to try and run it in clean sysnand mode it would fail. Although it normally should just not show up at all or tell you that an error has occurred and to redownload it from the eShop, not the black screen forcing you to power down :/
I'm not too sure why that's happening, I'd suggest posting on the thread I posted about the H&S inject.
Would you be able to describe step-by-step what you did exactly?
does the error occur on sysnand or on emunand?
When you dumped hs.app from sysnand, you restored the injected app to sysnand, yes? And then you did a separate dump of hs.app for emunand and separately injected into emunand, right?
If your Health and Safety apps were different between emunand and sysnand, then injecting a file that was dumped from sysnand into emunand may give problems like that. Or vice-versa, using the hs.app dumped from emunand to inject into sysnand.
You could probably get the .cia of the H&S app from an update pack downloaded online and replace your corrupted H&S app with a fresh one to start anew.