If it is so bad for humans to breathe the stuff how are the bees able to survive the dosage?
They don't. It kills them within a few months...
Our system has to last many year while accumulating damage. Theirs is reletively short lived....in the summer only 6 weeks. It does decrease lifespan of the bee somewhat.
OA is an irritant. I don't think that it is really bad for humans to get a whiff or two, but for liability reasons nobody wants to take any chances. A big dose can do major damage. Persistent breathing of low-dose OA over time will accumulate damage as well.