I think that the idea of "site control" falls appropriately on the shoulders of the qualified worker performing the task. OSHA speaks to barricades and the possibility of attendants if necessary. Safe approach distances are a required part of safe electrical work practices training. You'll be hard pressed to eliminate the on-lookers, however if they are far enough away from you, let them look?
The next question is how far away is safe?
I would think that the limited approach distance or the flash protection boundary (which ever is farther) would be a good place to start. Further consideration would have to be given to the type of work going on around you. This could easily extend your boundary.
