December 13, 1984 Appeal from the Workers' Compensation Board. During 20 years of employment as a laborer at Penn-Dixie Industries, Inc., claimant was exposed to stone and iron ore dust in the cement manufacturing process. After the plant was closed in 1975, he worked for other employers until he was hospitalized for coronary bypass surgery and chest abnormalities in October, 1978. Based on examinations and a lung biopsy taken during cardiac surgery on October 19, 1978, Dr. Frank Maxon, Jr., a pulmonary