I was stationed in Alaska the when Redoubt blew in 1989-90. The ash is more like grit than dust-like. You would feel the grit on your teeth and know that you didn't have your mouth covered properly. Another fear was the air filters on cars. Alot of people thought they wouldn't hold up. Another issue is air traffic in the area. We had all the F-15s and AWACS hangared. If the grit got into an engine it would be bad beans. Also, the foul sulphur smell was no fun either.