We winter about 850 hives indoors in single brood chambers in Manitoba,
Canada. We go into each of the buildings(2) at least once a day. The spores
from the dead bees only seem to bother us when we sweep the floor (a few
times a winter) and only if you don't wear a dust mask. The dead bees can
give you a cough and I once got a rash after sweeping the bees without a
mask. We run continuous exhaust fans to prevent CO2 build-up, which would
obviously be harmful to the bees and dangerous for checking the building,
and also run a ducted fresh air intake constantly. We also have auxillary
exhaust fans for when the weather is warmer (like now when it is plus 17
celcius outside) and we can add heat in cooler weather.

Mike Lewis