Air Filters on small stationary engines, are they adequate?

A piece of foam in a plastic case is all that some have!, I noticed to-day on our new scott Bonner mower that there was more dirt on the inside of the foam leading into the engine than was on the outside!!,Absoluteley useless!, and nothing cuts a motor out quicker than dust!, Anyway thats lawnmowers,But has got me wonderiing about Gen sets etc, although they don't create dust while operating there is a surprisingly amount of dust in the air most of the time when its dry,could be a issue if not thought of over a long period of time.

Cheers Axle