[ksmiley]

A roughly spherical asteroid of radius r has volume

4/3 * pi * r^3

Using Ceres as a benchmark for typical asteroid density, an asteroid of radius r has mass

[volume in meters^3] * 2077 kg/(m^3)

On the asteroid's surface, acceleration due to gravity is

[Gravitational constant] * [mass in kilograms] / (r in meters)^2

which simplifies to

(6.67384E-11 * 4/3 * pi * 2077 * r) m s^-2

If we mine on a 1km diameter asteroid, the dust we kick up will accelerate towards the surface at 2.9 * 10^-4 m/s^2. A dust cloud 10 meters high will settle in about five minutes.