the Mars atmosphere is so weak it barely exists. It's poisonous anyway of course, but even if an astronaut did take his helmet off there and hold his breath, his blood would boil from the almost vacuum like lack of air. An atmosphere that weak can't support large grains, even with Mars' low gravity, (1/3 gravity compared to Earth's), because the air is not strong enough to move anything larger than dust.
But I'm prepared to be wrong.
So an expedition goes to Mars, fully equipped to survive there apparently for, (a few months) at least. They either, don't make their spacecraft strong enough to withstand the dust storms, or they have no weather stations, (Mars Orbiter, Mars Reconnaissance, etc), that can tell when a dust storm is building, or both, and so just before they have to lift off, they send an expedition out into the (wherever) which cannot then get back in time. I think we could do better, even now.
By the way Ed, have you been following the building of the ISS? I'm really looking forward to one of the last Shuttle expeditions to the station. It delivers the seven-windowed Cupola module, which should be fantastic. It will allow the astronauts 360 degree views of Earth.