Hi Yes it is quite possible that this could be caused by a build up of static electricty dependant on the level of capacitance of the machine in question. I think there are types of footwear/shoe coverings that can prevent the discharge and also a substance that can be used infrequently on the floor that prevents static build up. Regards

The static is being produced by the friction between the brushes and the floor, a common enough problem. You can trail a small conducting wire or similar from the rear of the machine which will discharge the static as it is generated. As long as it has about 1 inch contacting the floor. J

A burn by static is quite possible depending on the size of the charge. Regards

Or anyone who has been hit by lightnng.

In this scenario the RCD trip time is irrelevant really. What was the Ze at the socket outlet in question, is it always the same socket outlet? IF the machine is double insulated then there should be no path to earth through the machine. Also then connecting the operator accessible metallic parts of the machine to a wire trailing on the carpet (however, you would not be buffing carpet) will have no affect on the electrical safety of the machine, and, this wire will have no connection to true earth through the machine, unless you modify the machine to connect a trailing "earthing" wire in the connection terminal box, IF the supply cord is 3 core. As far as the possibility of a burn from static, it is possible. If you are using metallic socket outlets then these will be earthed, and will provide a path for discharge, as long as they are correctly installed. Now, IF it is only one or two sockets the static discharge from the operators is giving an issue, then perhaps you should be looking at the other sockets in the premises to ensure that these have an adequate earth.