The company that I used to work for insisted that we stand on "insulating" rubber
while working on among other things lasers, so we chased around and found a large
piece a half inch thick....used it for years. When the project ended, a tech cut up the
rubber to use on his work bench and one day happened to lay the probes from an
ohmmeter on it..........dead short.

That piece of rubber probably created a better
path to ground then standing on bare concrete.

Woops.

Jim