Well, I made H2S on a few occasions in high school, and I always thought it has a powerful odor of rotten eggs. I have no doubt about it. You make a little H2S in a test tube, you will know, along with everyone else in the room and perhaps in adjacent rooms too.

I don't doubt that it deadens the sense of smell, I'm just saying it's nowhere near odorless on first contact.

Of course, I never made an amount large enough, nor did I stuck around long enough, for the sense impairment to occur.