PETAL (AP) — Authorities believe a father and son who died while working on a sewer lift station in Mississippi were overcome by odorless methane gas.

News outlets report that 45-year-old Terry West and his 20-year-old son Gage West were among three men working for a company that contracted with the city of Petal to work on the wastewater pump. The two were found unconscious Tuesday afternoon about 15 feet underground.

Petal Mayor Hal Marx says he thinks the workers were overcome by the gas and were unable to react quickly enough to escape. Forrest County Deputy Coroner Lisa Klem says autopsies will be performed to determine the official cause of death.