I agree with BOD that it sounds like you need to talk to the SAP. After all, presumably they'll be issuing you the Permit to Work (or LOA etc), so they'll need to see your RAMS anyway, and you know the setup.
What precisely are you doing, and what do you want a safe working distance from?
As others have said, you need to talk with one of your company’s HV Senior Authorised Persons. From your comments, I don’t believe that you hold an HV Competent Persons authorisation, so I am unable to comment further.
AFAIK, there is no clearly defined distance. It would depend on the nature of the equipment and on what work is to be done.
There is no simple "tick box" that a certain distance is required and that some lesser distance is prohibited.
Most such equipment is operated by DNOs, and they presumably have codes of practice regarding working space, this could be a useful starting point for similar equipment in private hands.
IEEE 1584 is a standard for working out arc flash and incident energy. This allows you to calculate the rating of protective clothing you need such that the blast from a short circuit is reasonably survivable. At 1m distance, you will be within the arc produced by a short circuit.
“An arc flash has the blast energy of several sticks of dynamite, and a temperature hotter than the surface of the sun”.
