Submitted Photo The flare stack at this well pad site, captured in drone footage from the New Town Fire Department, has been identified by the North Dakota State Fire Marshal as the cause of the Midnight Run wildfire near Keene in McKenzie County on Oct. 5.

A report released by the state fire marshal has identified the cause of two of the wildfires that engulfed western North Dakota in October as heat from natural gas flares combined with high winds and dry vegetation.

According to the report, investigations into the Midnight Run fire near Keene and the Dinwoodie fire near New Town, which ignited on Oct. 5, determined both were caused by flares at oil and gas wells operated by ConocoPhillips and Hess Corp. and situated next to agricultural land.

The investigation considered a number of hypotheses, according to the report, but ruled out arson, improperly disposed cigarettes, a possible electrical event and vehicles or farm equipment. The final conclusion was found after examination of the fire scenes and witness statements that heat from flare stacks was brought into contact with dry vegetation, and underlying ground fuels caused the ignitions.

According to the reports, the McKenzie County fires ignited just hours before state regulators asked oil operators to voluntarily shut down oil and gas wells in areas with high fire danger.

The Midnight Run fire spread rapidly, beginning after 3 p.m. on Oct. 5 near Highway 1806, due to the high winds and dry conditions, engulfing about 7,000 acres in McKenzie County.

The general origin area was determined to be grass vegetation and a dry stubble wheat field adjacent to a well pad site leased to ConocoPhillips, with the report identifying a flare stack 53 feet from the origin area. The report stated investigators made multiple failed attempts to interview or speak with any ConocoPhillips representatives.

The Dinwoodie sparked at about 5:30 p.m., spreading southwest for several miles and ultimately impacting about 2,048 acres. The general origin area was a canola stubble field 310 feet away from the flare stack on the Hess pad site. The site had five oil wells at the time of the fire and one dual tip flare stack.

According to the report, flares from the site can range in size from 6-60 feet, depending on the amount of gas flow, though Hess representatives said in an interview that the site would not be capable of reaching 60 foot flares.

Investigators noted that during an examination of the scene on Oct. 9, the flare stack had a sudden change in pressure, resulting in a burst or “burp,” causing the flare to grow and emit black smoke.

Hess representatives said the Dinwoodie site did not record any “burp” incidents that day, which cause hot oil or carbon particles to be dislodged due to pressure spikes. However, the company representatives did disclose that the pilot temperatures of the flare during the time frame of the fire was slightly higher than the normal temperature range of 1200-1800 degrees Fahrenheit.

Additional investigative reports are being finalized by the state fire marshal on the wildfires in Williams County, which led to two deaths and injured six others. Investigations of the Elkhorn Fire and Bear Den Fire on the Fort Berthold Reservation are currently in progress by the U.S. Forest Service and Bureau of Alcohol, Tobacco and Firearms, respectively.