I'd be curious to see a little more detail on the lungs issue. Maybe what I'm thinking are generating a misconception, but I'd like to see how they factor in.
I can see settling being a problem, but I would think it would be dwarfed by the issue of adherence.
I also start thinking that maybe settling is a bad thing if there is a chance of exhaling the dust.

__________________
Numbers are not case sensitive. (me)