## Facts

- Thelma L. Rutherford and her daughter sued for personal injury and wrongful death based on a decedent’s lung cancer after occupational asbestos exposure; the decedent was a lifelong smoker.
- Owens-Illinois, Inc. manufactured and distributed asbestos-containing products to which the decedent was allegedly exposed.
- The action was tried as part of consolidated asbestos litigation in Solano County.
- The trial court instructed the jury under a local order that, after specified predicate showings by plaintiffs, shifted to defendants the burden to prove their products were not a legal cause of the injury.
- The jury found for plaintiffs and allocated partial fault to Owens-Illinois, with most fault allocated to other asbestos entities that had settled.
- The Court of Appeal reversed, finding error in the burden-shifting causation instruction and in excluding a comparative-fault “tobacco company defense.”
- The California Supreme Court granted review.

## Issues

1. Whether a jury instruction may shift the burden of proof on causation to asbestos defendants in asbestos-related cancer cases after plaintiffs show exposure to a defendant’s defective product and that asbestos exposure generally can cause the injury.
2. What a plaintiff must prove to establish “substantial factor” causation for asbestos-related cancer where it is scientifically difficult to identify which fibers caused the cancer.
3. Whether reversal was required based on exclusion of a comparative-fault defense attributing responsibility to tobacco companies.

## Decision

- The court held the local burden-shifting causation instruction was generally unnecessary and incorrect under California tort law, and giving it was error.
- The court clarified that in asbestos-related cancer cases a plaintiff need not prove the defendant’s fibers actually caused the tumor; it is enough to show exposure to the defendant’s product substantially contributed to the plaintiff’s overall cumulative exposure and thus substantially contributed to the risk of developing cancer.
- The court concluded the erroneous instruction was nonprejudicial on this record when the instructions were considered as a whole.
- The court reversed the Court of Appeal’s judgment and left the plaintiffs’ trial judgment intact, including rejecting reversal based on the proposed tobacco-company comparative-fault defense.

## Legal Principles

- Causation in California tort law is governed by the “substantial factor” test; a cause is substantial if its contribution is more than negligible or theoretical, and it is not substantial only if its role is infinitesimal or purely theoretical.
- In asbestos-related cancer cases, a plaintiff may prove causation by showing, in reasonable medical probability, that exposure to the defendant’s defective asbestos-containing product was a substantial factor in contributing to the plaintiff’s aggregate exposure and increased risk of cancer.
- The plaintiff is not required to trace the path of any particular fiber or prove that fibers from the defendant’s product were among those that actually produced the malignant growth.
- Burden-shifting on causation is an exceptional doctrine limited to narrow settings (such as true alternative-liability situations or statutory presumptions) and ordinarily does not apply in asbestos cancer litigation where individualized exposure evidence is typically available.
- An incorrect causation instruction does not require reversal absent prejudice; courts assess the complete set of instructions and the record to determine whether the error likely affected the verdict.

## Conclusion

The California Supreme Court rejected generalized burden-shifting on causation in asbestos cancer cases, reaffirmed a substantial-factor standard focused on meaningful contribution to cumulative exposure and risk, and held that the erroneous instruction given here did not warrant reversal.


Rutherford v. Owens-Illinois, Inc., 16 Cal. 4th 953 (Cal. 1997)