## Facts

- After the 1979 accident at the Three Mile Island nuclear facility near Harrisburg, Pennsylvania, nearby residents sued owners/operators and related entities for personal injury and property damage allegedly caused by radiation releases.
- Plaintiffs’ proof of exposure and causation depended heavily on expert scientific testimony reconstructing how radioactive material dispersed and whether harmful doses reached plaintiffs.
- A key plaintiff expert, meteorologist Ignaz Vergeiner, advanced a theory that local atmospheric conditions and terrain trapped a radioactive plume over neighborhoods rather than dispersing it normally.
- Vergeiner rejected generally used dispersion models and relied on his own numerical model, a physical “water tank” simulation meant to mimic terrain effects, and a “plume movie” visualization.
- Vergeiner characterized his work as preliminary and illustrative of what might be possible rather than a validated reconstruction.
- The district court excluded Vergeiner’s plume-dispersion testimony under Federal Rule of Evidence 702 and the Daubert reliability framework.
- With the excluded testimony, plaintiffs lacked essential evidence of exposure/dose and causation; the district court entered summary judgment and related dispositions for defendants.
- Plaintiffs appealed, challenging the expert exclusions and the resulting judgments.

## Issues

1. Whether the district court abused its discretion under Federal Rule of Evidence 702 and Daubert by excluding plaintiffs’ expert testimony on plume dispersion and causation as unreliable and/or lacking fit.
2. Whether, after exclusion of that expert evidence, the district court properly granted summary judgment for defendants because plaintiffs could not establish a genuine dispute of material fact on causation.

## Decision

- The Third Circuit affirmed the district court’s exclusion of the challenged expert testimony.
- The court held the district court did not abuse its discretion in finding the plume-dispersion methodology insufficiently reliable under Rule 702/Daubert.
- The court affirmed summary judgment and related dispositions for defendants because plaintiffs, without admissible expert evidence, could not meet their burden to prove causation.

## Legal Principles

- Trial courts must act as gatekeepers under Rule 702 to ensure expert testimony is relevant and reliable before it reaches the jury.
- Reliability turns on scientific methodology rather than an expert’s credentials or assurances; courts may consider Daubert factors such as testability, peer review, error rate, and general acceptance.
- An expert opinion may be excluded where it rests on unvalidated simulations, speculative assumptions, or a failure to justify rejection of established scientific models.
- Expert testimony must “fit” the case by addressing the specific causal questions at issue; qualitative narratives that do not reliably support exposure/dose and causation may be excluded.
- Appellate review of Rule 702 admissibility rulings is for abuse of discretion, with substantial deference to a district court’s reasoned evaluation.
- When essential expert causation evidence is excluded in a toxic-tort case, summary judgment for defendants is appropriate if plaintiffs lack admissible evidence creating a triable issue on causation.

## Conclusion

The Third Circuit upheld the exclusion of plaintiffs’ plume-dispersion expert testimony as unreliable and insufficiently connected to proof of harmful exposure, and it affirmed summary judgment for defendants because the remaining record could not support causation.


In re TMI Litig., 193 F.3d 613 (3d Cir. 1999)