Page "Mass driver" Paragraph 24

One possible drawback of the mass driver is that it has the potential to send solid reaction mass travelling at dangerously high relative speeds into useful orbits and traffic lanes.

To overcome this problem, most schemes plan to throw finely-divided dust.

Alternatively, liquid oxygen could be used as reaction mass, which upon release would boil down to its molecular state.

Propelling the reaction mass to solar escape velocity is another way to ensure that it will not remain a hazard.