You need the right conditions - and a cause for the "potential" excess of electrons one way or the other. Dry powder snow is frictional or a thunderstorm within ~ 20 miles will help. Doing seismic we would sit and wait it out if a thunderstorm nearby for a couple of reasons, giving the ground crew belts, which you sometimes would see the spark and hear it on the radio, plus lighting up the recording electronics and jugs or electric dets and bombs was a potential issue. Also surprising how fast it builds up after discharge, literally seconds after grounding it's good to go again. Badge of honour for juggy's as to how hard they were! Funny looking down the longline to see people sit down so quickly!