They can be as low as a fraction of kiloton which is pretty small, not that you'd want it coming through your window.

The first thing I find odd is that this hasn't been taken up various parties who might want to have something to beat the apartheid state with. The corporate media obviouisly wouldn't bother with it, but the way it seems to be just one dude, albeit apparently qualified, saying it doesn't firm it up.

Needs digging into a bit more though.