T.O. 33B-1-1
(1)
Pre-exposure audible alarm and rotating or f lashing strobe-type (blinking, low intensity, warning
lights shall not be used) red visible warning signals within the enclosure which must be actuated
at least 20 seconds before irradiation can be started. Audible alarms will cease when radiation is
started, but visible warning signal will remain actuated during irradiation. The audible signal
shall be of a frequency or capable of producing a sound pressure level such that it can be heard
over background noise that may be present. Audible alarms are NOT required if the enclosure is
as small that it cannot be entered by an individual. An example of such an enclosure is a cabinet
X-ray system that has a small opening into which the part to be radiographed is placed but into
which an individual could not walk or even crawl without difficulty.
(2)
Suitable means of exit, so that any person who accidentally may be shut in can leave the
enclosure without delay.
(3)
Emergency shut-off switch(es) shall be provided within the facility labeled by a sign ‘‘EMER-
GENCY SHUTOFF’’ in red letters on a white background Sufficient number of signs and
switches shall be placed where they are visible and readily activated from any portion of the
interior of the protective installation. An emergency shut-off switch is NOT required if the
enclosure is so small that it cannot be entered by an individual. An example of such an enclosure
is a cabinet X-ray system.
(4)
Rotating or f lashing strobe-type (blinking, low intensity, warning lights shall not be used)
warning lights, inside the enclosure and outside all entrances to the enclosure. These lights
should be located such that they are visible to an individual entering or already inside of the
facility and will be operational when X-rays are being produced. An adequate sign should be
displayed near the lights to explain their function. Rotating/f lashing strobe-type (blinking, low
intensity, warning lights shall not be used) red warning lights will be located inside the enclosure
and red or yellow outside all entrances to the enclosure.
(5)
A pre-start switch, located inside the enclosure, so that if irradiation is interrupted by the
opening of a safety interlock, resumption of operation can only be accomplished after the prestart
switch has been reactivated. A pre-start switch is NOT required provided that:
(a)
The tube head is de-energized (or gamma shutter is closed) when an interlock is tripped.
(b)
The X-ray tube (or gamma shutter) can NOT be re-energized by merely closing the interlock.
To re-energize the X-ray tube, the entire time delay interlock system must be reinitiated at the
X-ray machine control panel.
d.
Exposure Limits:
(1)
Protective Installations: The exposure at any accessible region 2 inches (5 cm) from the outside
surface of the enclosure cannot exceed 0.1 mR (1 mSv) in any one hour. (The distance of 2 inches is
chosen as being the minimum practical distance from the barrier at which the exposure may be
measured.) The limit of 0.1 mR (1 mSv) in one hour assures with reasonable probability
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