HF is a particularly dangerous acid because of its unique ability among acids to penetrate tissue. Dermal exposure is the most common type of exposure to HF with the digits being the most often affected body part. Related compounds that have similar toxicity profiles include ammonium bifluoride, ammonium fluoride, potassium bifluoride and sodium bifluoride.
http://www.mnpoison.org/index.asp?pageID=151