You can hold fan where it does not spin , easy to do.  Also could even take off on S5's in a few minutes and really go to town with air.   Normally when I go to clean my rigs I use high pressure air due to I can make as much as I want, and it does not get cold and have to stop like canned air.  Not to mention if you are going through quite a few machines I would rather have 1 air compressor vs a box of canned air.

But yea... you should NEVER let it get that bad I'm surprised you did not have it getting really hot with that amount of dust. That has to be one of worst I have seen.