"An acquaintance mentioned in a email that in the resent "Minerals Engineering" **there is an article...by Meloy and Williams called "The Moon then Mars" in which they state that 400mph winds are common on Mars and a 5mm airborne particle moving at 400mph will puncture an unarmored suit.**

Can a 5mm particle even be airborne on Mars?"

400 kph may be somewhat common, but I don't think 400 mph is common and whether a 5mm object traveling at 400 kph could puncture a unarmored suit would depend on what this object was made of. I would imagine that some paint balls can be shot at around this speed. I would think that it could be possible for objects this size to be airborne on Mars but it would have to be a fairly rare event- wind erosion over billions of years would grind this size object down into a fine material. Plus not sure what mechanism would create this size object on Mars and if there was a mechanism to make this size common I would think that over time the wind would sort particles by size and density. Now if you went into an area and started changing the environment, you "could stir up some trouble":)