That would make me nervous also. But, there are so many substances that are incredibly dangerous when concentrated but incredibly useful when diluted. We had a saying in HAZMAT, “The solution to pollution is dilution.” There are some substances which are still dangerous in very low concentrations, but most are not.
The police officer who collapsed and almost died in the article the thread is about was trying to rub a very concentrated substance from his uniform. If it had been a concentration of 10% of the very same substance, he most likely would have had no noticeable effects at all.
You know, after I posted my comment, I thought back (after those endless hours spent in the dentist’s chair (Is It Safe? Is It Safe?) - it get’s hard to recollect...:-)) and googled some, and while I did discuss that HF stuff with him, the application may actually have been to the ceramic inlay prior to being fitted, rather than to the tooth itself.
Anyway, nasty stuff in concentrated form! And I have lab coat holes to prove it. LOL.