I believe you go noseblind to hydrogen sulfide very quickly. [1]

[1] https://dodtec.com/news/the-potential-dangers-of-hydrogen-su...

Perhaps "safer than CO" is fair, but "much safer than CO" may be a bit of a stretch. H2S is the #2 cause of fatal chemical inhalations in the workplace, behind CO:

https://www.bls.gov/opub/ted/2019/fatal-chemical-inhalations...