i touched a propane tank filled by a person with a crusted blood cut or hangnail on his thumb. i realized later i had cracked skin and a very small area of separation of my cuticle from my thumb nail such that purell stung a bit when applied. could i have been infected with hiv, hbv or hcv through my cuticle? there was no visible blood on tank and no blood or open wound on my thumb except as described. if no, please explain. thank you.

Welcome to the Forum.  I'll be pleased to comment.  No official agency such as the CDC or other professional organization would classify this as a risky exposure or recommend testing related to the sort of exposure you describe.  The event you described (I will not call it an exposure, it was not) was a no risk event.  Even with cuts , scrapes and abrasions present exposure to blood borne pathogens like HIV or the hepatitis viruses does not occur through indirect contact (i.e. when the contaminated material such as blood is first transferred to an inanimate object (the propane tank) and then on to another person.  There are several reasons for this, most importantly that these micro-organisms are very fragile and die almost immediately on contact with the air, at room temperature and with drying.  Further, for infection to occur, these pathogens need to be introduced ("injected") directly into the blood stream, not to simply contaminate a skin or cut surface.  For all of these reasons, IF the person you mentioned was infected with HIV or hepatitis and IF he transferred blood to the surface of the tank, there would still be no appreciable risk of infection.  there is no reason for concern and no reason for testing.  You are in the clear. 

I hope that my comments are helpful to you.  EWH

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Thank you, Dr. Hook.  2 follow on questions re HIV, HBV and HCV:

Direct answers, essentially repeating what was said before

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 I believe I click reset to end which I will now do. Thank you again.