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# Enforcement Guidance Concerning "Substantial Potential" for Overexposure or Release

## HPPOS-232 PDR-9111210339

See the memorandum from L. J. Cunningham to J. Liberman dated May 15, 1991.

An event presents a substantial potential when it was fortuitous that the resulting exposure or release did not exceed the limits of 10 CFR Part 20. If it is possible to construct a reasonable scenario in which a minor alteration of circumstances would have resulted in a violation of Part 20 limits, enforcement action should be considered due to the substantial potential for overexposure.

Enclosure 1 provides the final draft of enforcement guidance on what constitutes a "substantial potential" for overexposure, as used in C.4 of Supplement IV to 10 CFR 2, Appendix C. This input to the Enforcement Manual was provided following several enforcement actions where Regions applied a narrow interpretation of "substantial potential." The Severity Level III examples of Section C.4 of Supplement IV involve situations that present a "substantial potential for an exposure or release in excess of 10 CFR 20 whether or not such an exposure or release occurs.

An event presents a substantial potential when it was fortuitous that the resulting exposure or release did not exceed the limits of 10 CFR 20. The concern is not the significance of the resulting, or potential, exposure (Example C.1 of Supplement IV addresses exposures in excess of Part 20 limits), but whether the licensee provided adequate controls over the situation, as required, to prevent exceeding the Part 20 limits. No credit is given for luck. When taking escalated enforcement action for this example consider if it is possible to construct a reasonable scenario in which a minor alteration of circumstances would have resulted in a violation of the Part 20 limits. The following circumstances should be considered:
        - Timing - Could the exposure period have reasonably been longer?    An individual in the proximity of an unknown source of radiation receives an unplanned excessive exposure. Because of the duration of the exposure, no limits were exceeded; however, the individual could have reasonably stayed in the proximity of the source long enough to be overexposed.  
        - Source Strength - Could the radiation source have reasonably been stronger?    An inadvertent release results from a worker venting the wrong waste gas decay tank. Although the release did not exceed Part 20 limits, the same mistake could have resulted in venting a decay tank with enough activity to exceed the limits.  
        - Distance - Could the person have reasonably been closer to the source?    In example (1) above, the individual could have been overexposed by standing closer to the source of the radiation.  
        - Shielding - Could some unintended shielding have been reasonably removed?    A radioactive source was accidently left in an office area. Shielding afforded by a desk prevented the overexposure of an individual worker in the office. However, nothing prevented the source from being left in an area of the office, that would not have been shielded by the desk, where the individual would likely have been overexposed.

Regions were solicited for comments and they were incorporated in this final draft, with the exception of two comments in Enclosure 2 to this memorandum. The responses to these two comments were as follows.
        - Supplement IV clearly refers to the exposure and release limits in 10 CFR 20, not the 24-hour reporting requirements of 10 CFR 20.403 (b) [or "new" 10 CFR 20.2202 (b)].
        - A Severity Level III violation does not have to present the risk of a serious violation of Part 20; there is no reference to serious violations in example C.1 of Supplement IV. An event meets the "substantial potential" test if the licensee's controls were not effective in preventing a violation of Part 20 and the consequences of the event were a matter of chance.

**Regulatory references:** 10 CFR 2

**Subject codes:** 12.7

**Applicability:** All

Page Last Reviewed/Updated Wednesday, October 18, 2017