Pre-exposure audible alarms and rotating red visible warning signals within the enclosure that
must be actuated at least 20 seconds before irradiation can be started. A sign shall be displayed
near these devices to explain their function. Audible alarms will cease when radiation is started,
but visible warning signal will continue throughout exposure.
Suitable means of exit, so that any person who accidentally may be shut in can leave the
enclosure without delay.
An emergency shut-off switch shall be provided within the facility labeled by a sign EMER-
GENCY SHUT-OFF in red letters on a white background. Sufficient number of signs and
switches shall be placed such that they are visible and readily activated from any portion of the
interior of the enclosed installation. If only one emergency shut-off switch is provided, it should
NOT be adjacent to personnel exit door since the door itself can act as an emergency shut-off
device. The switch should be located as far from the door as is practical.
Rotating or f lashing strobe-type (blinking, low intensity, warning lights shall not be used)
warning lights, red inside the enclosure and red or yellow outside all entrances to the enclosure.
These lights should be located at approximately eye level and shall be operational. An adequate
sign shall be displayed near the lights to explain their function. If a) the shielding provided by
the roof is less than that provided by the walls, or b) there is direct access from the roof into the
exposure room, then one of the following shall be provided: a) a rotating f lashing strobe type
(blinking, low intensity, warning lights shall not be used) red or yellow light on the roof with an
explanatory sign adjacent to it, or b) a sign indicating Restricted Area, Contact (Name, Ext.)
Before Entering on all permanent accesses to the roof and on the roof itself so that it will be
visible to anyone attempting to climb onto the roof.
A pre-start switch, located inside the enclosure, such that if irradiation is interrupted by the
opening of a safety interlock, resumption of operation can only be accomplished after the pre-start
switch has been reactivated. A pre-start switch is not required provided that:
The tube head is de-energized (or gamma shutter is closed) when an interlock is tripped.
The X-ray tube CANNOT be re-energized by merely closing the interlock. To re-energize the
X-ray tube, the entire time delay interlock system must be re-initiated at the X-ray machine
control panel. (Comparably, the gamma shutter cannot be opened without proceeding through
the standard system setup/initiation procedures.)
The exposure at any accessible and occupied area one foot (30 cm) from the outside surface of the
enclosure does not exceed 2 mrem (20 mSv) in any one hour and the exposure at any accessible and
normally unoccupied area one foot (30 c) from the outside surface of the enclosure does not exceed 20
mR (200 mSv) in any one hour. (Access to normally unoccupied areas in which doses could exceed 2
mrem (20 mSv) in any one hour or result in exposures to members of the public exceeding 100 mrem (1
mSv) per year must be secured or continuously monitored to preclude personnel entry.)
For X-ray installations, these exposure limitations shall be met for any X-ray tube to be used in
the enclosure and operating at any specified mA and kVp rating within the manufacturers
No beam limiting device or filter shall be used during these tests unless such devices and filters
are permanently attached to the X-ray tube or gamma exposure device and the unit cannot be
operated without their use.
The radiation source and beam direction shall be positioned and oriented so that the highest dose
rate will be encountered in the area under test provided that such positioning and orientation will
serve a practical purpose in normal usage.