This is what the filter looks like after 1 day of sanding, the fan is a 24" high velocity 4,000cfm motor.

I'm in my 50's now, I recall when I use to do this type of demolition work frequently 20 years ago. You would blow your nose afterword's, and see black coal dust in the discharge. Face mask was the only defense, now that has all changed. We will never go back to the old way, of just a face mask. The filters you guys sent me work fantastic, and we are especially thankful they are washable!!!@ We deployed 2 fans, moving a total of 22,000 cubic feet of air per minute thru the fi