Tours are normally permitted only during access or down days when a radiation survey has been done and magnet power systems have been secured.
A tour of the CHESS area may be possible if that area is in Bypass; check with the CHESS operator.
In rare situations the possibility of a tour in specific CESR locations (most commonly only to the L0 catwalk, not beyond the chained-off section just south of the stairway to CLEO) during an interlock-set access should be discussed with the CESR operator, preferably well ahead of the tour time. Granting of permission for such a tour should not be assumed, may depend on several conditions, and specific limitations may be imposed.
If interlocks are set, each tour participant would need a white key to enter the CESR-synchrotron perimeter and understand how to use it: each key holder is responsible for the timely return of the white key after the tour.
At the CESR operator's discretion, only the guide would carry a white key and intentionally break the interlock on the way into a controlled area. In this situation both the guide and operator would independently keep headcounts prior to entering and after exiting the controlled area, verifying that everyone is accounted for.