There was another fire in the McKenzie County area where the oil well explosion occurred, but it was small.
Williams County Sheriff Scott Busching said a pumping unit on a tank that separates saltwater from crude oil caught fire and was quickly extinguished.
"There was no explosion, nobody was hurt, and nobody was even there," Busching said.
The recent fatalities bring to three the number of oil patch related deaths since July 1, said Bryan Klipfel, director of the North Dakota Workforce Safety and Insurance agency.
North Dakota recorded five oil field-related deaths in fiscal 2011, up from three in fiscal 2010, Klipfel said.
The number of injuries in the state's booming oil patch jumped from 747 in fiscal 2010 to 1,897 in fiscal 2011, a more than 150 percent increase, he said.