Surely military and civil helos have been flying in recirculating dust for donkey's years in desert and unprepared sites. Has this ever caused significant engine problems?
I once did a stint of desert ops that involved 2 jetrangers operating for about 250/300hrs with extremely dusty conditions at each T/O and landing (average sector probably a bit under an hour) visibility in recirculating dust often 10m at touchdown.
The Chief Engineer's only comment on our return was that he'd never seen such clean engine internals.