OKLAHOMA CITY (AP) — A second man who was injured in an explosion at an Oklahoma oil refinery has died.

A University of Oklahoma Medical Center spokesman says Russell Mann of Davis died Tuesday at the Oklahoma City hospital.

Mann was injured and Billy Smith of Pauls Valley was killed Sept. 28 when a boiler exploded at Wynnewood Refining Co., owned by CVR Energy Inc. of Sugar Land, Texas.

CVR officials have said the explosion occurred as the boiler was being restarted following scheduled maintenance and upkeep, which resumed the following day.

CVR issued a statement saying an investigation into the blast continues and CEO Jack Lipinski expressed "heartfelt sympathies" to all affected by the blast.

A U.S. Department of Labor spokeswoman also said an investigation is ongoing and declined further comment.