A reasonable portable machine to crush glass into cullet to make recycling materials?

Saw a program on BBC2 i think where a man was living environmentally friendly,they got a machine and made cullet (crushed glass) .They used it for some sort of insulating/heat trap equipment. It was fine like glass , additionally i would ask
1)Is it safe
2)Could it be used in
a) Gardens
b) Areas of grass to convert to parking area’s
Thanks if you respond fully i would be greatly appreciative
Cheers