Basically using a compressor to "blast" air through the rug from backing taking dry soils out through the pile. Messy and time consuming. Probably it's best use is for conservation with delicate rugs rather than day to day rug cleaning.
An air duster for us is invaluable.
You can use it in various ways.
Post vacuuming and using a badger, you can still retrieve fine dry soils.
Post washing you can still retrieve fine dry soils.
So it's really helps in getting to where you previously couldn't reach.
If you have a longer pile like a Flokati or a sheepskin it's amazing at getting to what's been trapped,left behind.
Post washing it's also great for fluffing up the pile using hand tools.
If you are using badgers or similar, you will or should have things in place to either capture or direct the dust to where its acceptable.
Provided the air duster is used as described, it's rarely an issue.
As a side note the correct mask and eye protection should be used at all times.
We also flap dust rugs on occasion but that's a different topic.
Hope that may be helpful.
All the best. J