20.0 Facility Design Criteria
20.1 General
- Plans for shielding and shielding calculations shall be reviewed and approved by the RSO.
- Whenever shielding is required it shall be designed to resist mechanical damage. (Shielding shall be constructed such that it will not cause a hazard due to collapse.)
- Shielding shall be adequate (without cracks, gaps or voids) to reduce exposure to within the limits described in the following.
- Dose rates in Unrestricted Areas shall not exceed 2 mrem/hr and 50 mrem per year.
- Dose rates in any accessible frequently occupied region within a Restricted Area shall not exceed 5 mrem/hr at 30 cm outside of the shielding.
- Dose rates in any accessible but unoccupied area within a Controlled Area shall be below 100 mrem/hr at 1 ft. from outside of the shielding.
NOTE: Radiation areas and High Radiation areas must be denoted as prescribed in Chapter 16.0 (Restricted Area Designation Procedure).
20.2 Interlocks, Warning Devices, and Emergency Switches
- When conditions require installation of a radiation producing machine in a shielded enclosure, all access doors shall be equipped with interlocks due to the potential of the machine creating a High Radiation Area. These interlocks will shut the machine off if entry is attempted during the machine operation.
- In shielded enclosures, an emergency switch shall be placed within the enclosure allowing anyone to shut down the radiation machine. This switch is to be clearly labeled and shall not be capable of being reset from outside the enclosure.
- When a safety interlock system has been tripped, it shall only be possible to resume operation of the machine by manually resetting controls at the position where the safety interlock has been tripped, and lastly at the main control console.
20.3 Postings
Each machine capable of producing ionizing radiation shall be labeled as follows:
"CAUTION – X-ray Device Produces Ionizing Radiation When Energized" And Other Signs or Labels as Required
Standard signs can be obtained from EH&S. Additionally, the following information shall be posted on or near the machine where it may be readily observed.
- The name of the person responsible for the machine.
- The name of each authorized operator.
- Operating procedures, including general and specific safety instructions.
- Emergency procedures giving the name and day and evening telephone numbers of the RSO.
- Personnel monitoring requirements.
20.4 SPECIAL NOTES
- Where an authorized user is in constant attendance during the temporary operation of a radiation producing machine, warning signals and barricades may be an acceptable substitute for shielding when approved by the RSO. The RSO's approval and a description of the devices and their use must be in writing and posted in the immediate vicinity of the machine(s).
- When interlocks have been bypassed in order to facilitate experimentation, a survey of the radiation levels in the area(s) to be entered must be conducted. Bypassed safety systems and associated operational procedures must be PREAPPROVED IN WRITING by the RSO and only used under the specified conditions. When interlocks have been bypassed, the Authorized User must be in constant attendance during all procedures.
- Electron microscopes and X-ray diffraction machines will be surveyed for safe operation before their first use, following any repairs, and annually.
Special Considerations for Certain Radiation Producing Machines Other Than Accelerators
Electron Microscopes
Normally these are low hazard devices. Operators need not wear personal dosimeters. The Radiation Safety staff will perform a radiation survey annually. These devices must not be modified in any way that would reduce the effectiveness of the intrinsic shielding. These machines will be posted with appropriate signs if radiation survey results indicate any hazard.
20.5.2 X-ray Diffraction Machines
The primary beams from these devices may be as high as 400,000 R/Minute. The chief hazard is hand exposure to the hands while setting up an experiment. Exposure to the primary beam will cause injury to the skin. The scattered beam also can exceed acceptable limits and may be as high as 150 R/Hr at 10 centimeters. Operators must be authorized by the RSO and are required to be trained in the safe use of x-ray diffraction devices. Users are required to wear both finger and whole body dosimetry when working in an open beam configuration. Annual surveys of each device will be made by Radiation Safety staff. Portable shielding is usually needed to reduce exposure levels from scattered radiation. Users may be required to have survey instruments present and to perform a radiation survey after a setup of the machine to ensure that shielding, collimators and beam stops are properly placed.