Trapped sewer gas is being blamed for a house explosion near Freeborn that critically injured a 75-year-old man. The explosion occurred Friday afternoon about a mile north of Freeborn, and Ralph William Yotter was flown to the Twin Cities with burns to his face and body. The house is a total loss. Investigators say that the sewer gas apparently entered the home from a septic tank after Yotter moved some appliances and failed to cap the drain line. The gas then sparked when Yotter turned on a light switch. Yotter and his wife did not live in the house at the time. He was listed in Critical condition at Regions Hospital in St. Paul as of Tuesday. His wife was outside at the time of the explosion and suffered only minor injuries.