On Sep 24, 2013, at 12:41, Dave  wrote:

> Are you sure on the NH4F safety? My understanding is that this simply
> dissociates into HF once it is combined with water.
>
> Whenever I use etchants with NH4F or ammonium biflouride I treat them like
> HF.

My understanding - with the caveat that I'm very much *not* a wet etch or safety
specialist - is that the general health hazard of NH4F is similar to HF (free
fluorine radicals getting into the body and screwing with cellular ion transport
processes, aka "fluorosis"), but the severity is not *quite* as high.  NH4F (as
well as Fujifilm Pad Etch) shows as NFPA health hazard class 3, while HF is 4.
The MSDS does recommend the use of calgonate for NH4F exposure to skin.  But
you're absolutely right that you still want to be very careful with NH4F, and
take spills and splashes seriously.  Just because it's not pure HF doesn't make
it innocuous.

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