## Facts

- Thousands of plaintiffs alleged injury from long-term exposure to radioactive emissions (including radioactive iodine) from the Hanford Nuclear Reservation.
- Plaintiffs sued corporate contractors that operated Hanford under federal contracts, bringing claims as “public liability actions” under the Price–Anderson Act.
- The district court organized the litigation into phased discovery; Phase II was designated to address generic causation and other common issues, reserving individual exposure and specific causation for a later phase.
- At the close of Phase II, the district court granted defendants summary judgment.
- The district court treated as dispositive whether each plaintiff had received a “doubling dose,” defined as a radiation dose that would double the risk of illness compared to the general population, and concluded plaintiffs had not shown sufficient exposure.
- The district court’s approach also resulted in exclusion or discounting of portions of plaintiffs’ expert causation evidence.

## Issues

1. Whether the district court improperly decided individual exposure and specific causation at the Phase II stage, contrary to its phased case-management structure.
2. Whether the district court erred by requiring proof of exposure to a threshold “doubling dose” as a legal element of generic causation to survive summary judgment.
3. Whether the district court abused its discretion in its treatment of plaintiffs’ expert causation testimony under evidentiary standards governing reliability and relevance.

## Decision

- The Ninth Circuit reversed the district court’s grant of summary judgment and remanded for further proceedings.
- The court held the district court prematurely resolved individual-causation and exposure questions during a phase intended to address generic causation and common issues.
- The court held the district court erred as a matter of law by imposing a rigid “doubling dose” threshold as a prerequisite to proving generic causation.
- The court concluded the district court’s causation framework improperly constrained its evaluation of expert testimony and warranted reconsideration consistent with proper evidentiary standards.

## Legal Principles

- In toxic-tort and radiation-exposure litigation (including Price–Anderson public liability actions), generic causation and individual causation are distinct inquiries and must be addressed in accordance with the litigation’s phased structure.
- A court may not require plaintiffs to prove exposure to a specific numerical “doubling dose” threshold as a mandatory element of generic causation or as a universal requirement to defeat summary judgment.
- Causation may be supported through multiple scientific lines of proof; epidemiological risk concepts may inform analysis but do not create a categorical legal prerequisite.
- Expert causation testimony must be assessed under applicable reliability and “fit” standards, not excluded solely because it does not conform to a court-imposed dose threshold.

## Conclusion

The Ninth Circuit reinstated the plaintiffs’ claims by holding that the district court improperly collapsed phased proceedings into an early adjudication of individual causation, and by rejecting the “doubling dose” requirement as an erroneous legal prerequisite for generic causation and for evaluating expert evidence.


In re Hanford Nuclear Reservation Litigation, 292 F.3d 1124 (9th Cir. 2002)