(1) On open-beam configurations installed after January 1, 1978, each port on the radiation source housing shall be equipped with a shutter that cannot be opened unless a collimator or a coupling has been connected to the port.
(2) A visible indication of the status of the shutter shall be provided, example being a red-light indicating beam "on" or a green light indicating beam "off".
(a) The device shall be tested, no less than every six months, to ensure operations will not continue without a properly functioning warning device.
(b) On equipment installed after January 1, 1978, this device shall be of fail-safe characteristics.