Oooh, I know this, kind of!
I did my work experience for what was then MAFF, and there was an official mites/g total that was considered unacceptable. You hoover the beds/carpets etc, take a sample of the dust, wash and filter it then count how many creepy-crawlies are left on your filter paper, then you work out how many per gram that is.

I think the number is lots :(

Obviously the amount of dust you get per bed/per room is also taken into consideration.

I only got to do that for a day though, the rest of the time there was working for a man called Bushy who had an interest in bees.
(wellgroomedwookiee is a filthy-minded hobgoblin, Wed 3 Dec 2008, 17:22, Reply)