Hurricane Sandy has projected wind speeds that heighten at about 90 mph.
So lets say some poor fool decides to go to the beach with this wind but not much rain, and stands observing 1 meter away from where the sand begins. It's pretty plausible that 90 mph winds could get a grain of sand moving, but how dangerous is that grain of sand?
Well, lets say it takes the whole meter for the sand to get up to speed, and its final velocity is 90 mph just before it hits you. This is a velocity of 40.0 m/s. Using the equation (v)^2=(vo)^2=2ax, you find an accelleration of 808.02 m/(s)^2. If the grain of sand has a mass of .00000067 kg (.67 mg), then the net force felt by the grain of sand is .00054 N.
The average muzzle velocity of a gun is 120 mph, only 30 mph (13 meters/s) faster. However, not only would a bullet's force be spread over a larger surface area, resulting in a lower pressure, but the force wouldn't be constant, since it would be slowed if only slightly by resistance. Whats more, a bullet lodges itself within a human, and "dangerous" is a standard that's reached WELL before deadly.
So is a grain of sand dangerous? The grain of sand would generate a pressure of around .0119 psi. Considering the human body can withstand up to 50 psi on sudden impact, I'd say the sand isn't going to do anything traumatic. It might sting, especially if it gets in your eyes or throat, but it's certainly no bullet.