## Facts

- Ralph R. Olson worked as an underground uranium miner for two employers in alternating periods from 1958 to 1971.
- His last employment was with Federal American Partners from January 18, 1971, to December 29, 1971.
- Olson became ill and died on May 23, 1973, from lung cancer.
- Olson was a habitual cigarette smoker.
- His widow, on behalf of herself and a dependent child, sought benefits under Wyoming’s former Occupational Disease Law, asserting lung cancer was a compensable “malignancy caused” by ionizing radiation and that Federal American Partners was solely liable as the last employer where Olson was “last injuriously exposed.”
- The claimant presented medical expert testimony that lung cancer rates are high among uranium miners, higher among miners who smoke, and that Olson’s cancer most probably resulted from occupational radiation exposure.
- The expert also testified that radiation exposure within federal permissible limits would not be medically “injurious” in the sense of contributing to or promoting cancer.
- The employer introduced evidence that radiation levels in its mines were within federally permissible limits and contested whether the disease could be attributed to Federal rather than to earlier mining employment and smoking.

## Issues

1. Whether the claimant proved, by a preponderance of the evidence and by competent medical authority, that Olson’s lung cancer was a compensable malignancy caused by ionizing radiation arising out of and in the course of employment.
2. Whether the claimant proved Olson was “last injuriously exposed” to the hazards of the disease while employed by Federal American Partners, making that employer solely liable under the statute.

## Decision

- The Wyoming Supreme Court affirmed the district court’s denial of benefits.
- The court held the claimant did not meet the statutory burden to prove, through competent medical authority and by a preponderance of the evidence, that Olson’s lung cancer was causally related to employment with Federal American Partners.
- The court also held the claimant failed to prove Olson was last injuriously exposed to ionizing radiation while employed by Federal, as required to impose liability on the last employer.
- The court deferred to the trial court’s fact-finding where supported by substantial evidence and declined to reweigh conflicting inferences.

## Legal Principles

- Under Wyoming’s former Occupational Disease Law, the claimant bears the burden to prove statutory causation elements by a preponderance of the evidence and by “competent medical authority,” including direct causal connection, proximate cause traceable to employment, and that the disease did not arise from hazards equally encountered outside employment.
- The “last injurious exposure” rule places sole liability on the employer in whose employment the worker was last injuriously exposed to the disease hazard; mere exposure is insufficient without proof the exposure was injurious.
- Medical testimony framed as probability may be insufficient where it does not satisfy statutory requirements as applied to the alleged last injurious exposure, especially when significant non-occupational and prior-occupational risk factors (such as heavy smoking and earlier mining exposure) remain plausible competing causes.
- Evidence of regulatory compliance, combined with medical testimony that exposures within permissible limits are not injurious, supports a finding that the claimant failed to prove injurious exposure with the last employer.

## Conclusion

The court affirmed denial of occupational disease benefits because the claimant’s medical proof did not establish statutory causation tied to the last employer and did not show that the worker was last injuriously exposed to ionizing radiation during employment with that employer, particularly in light of prior mining exposure, heavy smoking, and evidence that the last employer’s radiation levels were within permissible limits.


Olson v. Federal Am. Partners, 567 P.2d 710 (Wyo. 1977)