I learned about this the hard way,(as with most things), while taking down a PVC vacuum transfer system for documents (the type that sends little bottles through it).
The sttic zonk knocked me clean off of an aluminum ladder, and I sprained my ankle. This gave me some time to figure out what went wrong.
In retrospect, 25 years or so later, I was very lucky to have been just a few feet off of the ground...S
