Originally I added it because the post was discussing potentially using poison gas to fumigate his stock.
It's ok if it's poisonous to humans...
In chat Rob pointed out to me that I might be imposing a view on the question and that safety was not the intended focus anyway.
@Matt I think it does subtly change the question it suggests that he is concerned about safety when he is not (he just wants to kill the bugs and their eggs), and by adding the tag you were asserting your own safety-consciousness upon him and anyone else who answers his question. For example, following the same logic you could add the safety tag to any question that talks about something with sharp edges because you could cut yourself.
Those points I later agreed with and removed the tag. By my earlier logic I should go an put the safety on every question since anything could be a safety issue. That of course is just silly.
My current stand point is that having that tag on that question was in error which I corrected.
Rob suggested that I bring it to Meta to let the community have an opinion.