SPRINGFIELD, Ill.—A retired coal worker's lung disease can be presumed to be caused by his former job, even though he was a smoker for nearly 40 years, an Illinois appellate court has ruled.

A workers compensation arbitrator and the Illinois Workers' Compensation Commission had ruled that cigarette smoking caused William Gross to develop chronic obstructive pulmonary disease, among other conditions, and that he should not be able to collect workers comp benefits.

Mr. Gross, who worked in various roles at two above-ground coal mines from 1965 to 2003, retired from Freeman United Coal Mining Co. in 2004, records show. He applied for workers comp benefits in 2005, claiming that his career caused him to develop pneumoconiosis, histoplasmosis and COPD.

Dr. Joseph Renn, a pulmonary specialist testifying on behalf of Freeman United, contended that Mr. Gross smoked a pack of cigarettes per day, and that such use “would almost certainly have resulted in various tobacco smoking diseases.”

While the doctor agreed that coal dust could have caused Mr. Gross to develop COPD, he argued in a report that “none of the (claimant's) diagnoses were either caused, or contributed to, by his exposure to coal mine dust.”

Mr. Gross dropped his pneumoconiosis and histoplasmosis claims. However, he argued that evidence in the case should allow for a presumption of COPD caused by his former job.

The 4th District Illinois Appellate Court agreed Friday, saying Mr. Gross' coal mining work should be considered a causative factor in his lung problems under Illinois' Occupational Diseases Act.

“The occupational activity need not be the sole or even the principal causative factor, as long as it is a causative factor in the resulting condition of ill-being,” the court ruled 4-1.

The appellate court said Dr. Renn could not reasonably prove that coal dust wasn't a contributing factor in Mr. Gross' COPD diagnosis.

“Where the undisputed evidence is that the claimant had nearly 40 years of exposure to both coal dust and cigarette smoke, we believe that the commission's finding that his COPD was solely caused by cigarette smoking is against the manifest weight of the evidence,” the Springfield, Ill.-based appellate court ruled.

The case was sent back to the Illinois Workers' Compensation Commission to determine the extent of Mr. Gross' disability.