Back in 1963 in Culdrose some static tests were done on a Wessex MK5.
From memory up to 100000 volts were generated in less than 1 second. Obviously the current was minute otherwise I'm sure there would have been some big problems. This meant that after you earthed the hook, if you let go, the static would be back within 1 second. This meant you either had to re-earth or have a line attached to prevent build up.
On one occasion when I was in a low hover, a Royal Marine sergeant jumped out but held onto the door handle. He performed a beautiful double summersault with pike on landing! The build definitely varied with both surface and weather conditions but I don't recall anyone being injured. I've had worse shocks off my car engine spark plug leads.
Small helicopters never seemed to be a problem and thick rubber gloves seemed to do the job.
