One of the top 5 nastiest checmicals I have encountered during my career is Hydrofluoric Acid and Hydrogen Fluoride (HF). And it just amazes me that humans can convenience themselves that these chemicals are not “really that hazardous”. TRUST ME (and NIOSH), HF has earned its place in my Top 5. Of course, HF is not nearly as prevalent at Anyhrous Ammonia or Chlorine (two more of my top five) and this is a GOOD thing as HF is #2 on my list, only behind Phosgene (COCl2). And yes I have worked with DiBorane and Tert-Butyl Hydroperoxide (both of which are 4-4-4 in the NFPA 704 Diamond), but in my experiences we GREATLY LIMITED these two HAZMATs in quantatity, but when I worked with HF, COCl2, Cl2, NH3, and Br I was working with tons of the materials and thus much great risks.
HF has a “double-whammy” in that it can be readily absorbed as a liquid and the liquid converts to a gas quickly at standard temperature and pressure; and inhaling HF can be deadly (IDLH is 30 ppm). But here is some really good info from OSHA on HF and it’s hazards: