"Richard, I believe your calculations are too conservative."

I know they are way too conservative.  For instance I treat thru a hole in the bottom board.  And, I seldom do much to even block the entrance if the wind is from the south.  I am pretty sure far less than half the dose goes up to where honey supers are in my tests based on fog density coming from various places on the hive.  On the other hand I have heard of people getting creative and treating from the top.  In that case I suspect far more than half remains in the upper boxes.  Plus there is no hard data other than some from Europe, as I recall, that says darned little gets in honey up in supers.  So little that it does not change the oxalic acid content of the honey very much as "natural" honey contains some oxalic acid.  I suppose that natural amount varies all over the map depending on what species of plants the bees got the nectar from.  But, I really do not know that to be true.  So, there are lots and lots of unknowns and I am lazy so did the simplest calculation possible knowing it was likely a worst possible case.  If a worst case seems safe anything else is going to be safer.

I was most surprised by how much it took in air breathed for hours to get you in trouble.  I would have guessed that a lot less than 5 mg/l would have been lethal.  In a way this is really good news.  Very little will make you cough really hard and force you to get out of breathing any more.  I have known bunches of people that breathed in chlorine gas which will likewise give you a bad cough.  The ones I know all recovered in a few hours, including myself.  A good shot of codeine cough syrup really helps.  But I recently read about someone who was exposed to what I would consider a mild amount that died.  I suspect he had a heart attack or stroke and the death was not due to direct damage from the chlorine.  Or perhaps he had a case of walking pneumonia and the added stress simply flooded his already damaged lungs?  This links back to what I said about a dose killing an occasional person when most people would survive several times that dose.

In the case of oxalic acid sublimation fog there really is no excuse for anyone to get exposed.  Effective breathing protection devices are cheap and easy to find.  The only problem is people with claustrophobia often can not mentally stand to wear such devices.  Those people simply should not use oxalic acid vaporization.

Dick 

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