"Any beekeeper who uses a N95 mask for OA vapor is in for a disagreeable
treat."

No bee keeper is exposed to oxalic acid vapor.  What you are exposed to is tiny particles of oxalic acid that condenses a fraction of an inch from the vaporizer forming tiny oxalic acid crystals.  I can not personally testify to the effectiveness of a N95 mask at stopping these particles as I use a 3M half face shield respirator personally.  However, I do know that due to the full beard I wear it is impossible to get a seal from any respirator or dust mask.  I have seen this demonstrated with 100% clearity in lab tests where the leakage was always enough to cause the wearer to cough due to leakage when tested with tin chloride (stannic chloride) vapor.  If you want a 100% effective seal you simply can not have any beard in any area between your skin and the seal on the respirator.  That is the reason chemical plants universally have a no facial hair rule for employees that work in any area where they might be exposed to toxic chemicals.  A stach is generally permitted as it is not a sealing surface.  Generally that any employee rule applies to anyone allowed inside the plant gates.  Perhaps sales people who only go to the offices may be exceptions.  Years ago this rule did not exist as respirators were used you gripped between your teeth and had an attached nose clip.  Those got real uncomfortable rapidly so could not be used if the exposure was going to be an hour or two.  I have not seen one of those for 40 years and doubt if they are allowed anymore.

With that background I will tell you I have stood in the middle of a cloud of desublimed oxalic acid coming out of hives a number of times and have never once detected the slightest throat irritation from such exposure.  I assume the particles of desublimed oxalic acid are so course my beard functions as an effective filter.  I also know several who use N95 masks and experience no problems with oxalic acid exposures.  I personally would not do it, but others tell me it works.  Under the best of circumstances the seal of an N95 is pure crap compared to a half face shield respirator.  I would not even use an N95 for wood dust personally.  The main medical use is to avoid splashes and gobs of coughed up mucus I think.  None of those respirators will stop a virus.  Wearing one also likely reminds people to not touch their face.

Dick

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