Your experience is interesting and thank you for sharing it.
Spudgunr on Cast Boolits calculated the amount of lead in the air :
I found an OSHA letter stating the max lead concentration for an indoor range is 50 micrograms per cubic meter (this should be the PEL, permissible exposure limit, based on breathing this for an 8 hour shift).
At lead's melting point (621F) the vapor pressure is 4X10^-7 Pa (400 parts per trillion)
@815F its 1X10^-4 Pa (1 part per billion)
@1300F it is 1Pa (10 ppm)
So, at 815F that is 12 micrograms per cubic meter, at the molten leads SURFACE, 1/4 of OSHA's PEL (and you KNOW they are conservative!)
870 degrees - 5X10^-4 Pa - 60 micrograms per cubic meter (just above OSHA PEL)
925 - 1X10^-3 Pa - 125 micrograms per cubic meter (2.5 times OSHA's limit for an 8 hour shift).
1000 - .01 PA (.1 ppm) = 1200 micrograms per cubic meter.
1100 (Added in on the edit just because this value was mentioned above) .13 PA - 15,600 micrograms per cubic meter, three hundred times the OSHA guidelines.
This came from NIOSH STD 78-158, just multiply by 1000 to get micrograms.
I am of the opinion that one should use forced air circulation over your casting pot. People should be mindful of the lead particles that collect not only on surfaces, but on clothing.
Lead particles don’t have to be visible, there are billions of particles floating around in front of you that you cannot see. When they get micron size they will float, can float for weeks given air circulation. Of course human lungs are very good at absorbing these things and passing them directly into your blood stream.
I would recommend buying lead wipes and wiping off the areas around your casting pot. Apparently people have bought lead testers at Home Depot and found very high lead levels in their casting area. Might be worth looking into to determine the extent of your problem.