(1) Open-beam configurations shall be provided with a readily discernible indication of:
(a) X-ray tube "on-off" status located near the radiation source housing, if the primary beam is controlled in this manner; and
(b) Shutter "open-closed" status located near each port on the radiation source housing, if the primary beam is controlled in this manner.
(2) Warning devices shall be labeled so that their purpose is easily identified. On equipment installed after January 1, 1978, warning devices shall have fail-safe characteristics.