High pressure dislodged the equipment, causing it to smash Krajewski in the chest and abs, at about 3:30 p.m. Saturday.
The North Dakota Medical Examiner's Office says that a Duluth, Minn., man killed at a hydraulic fracturing site near Watford City suffered chest and abdominal injuries when he was hit by oilfield equipment.
The Tuesday report rules the death of 49-year-old Halliburton employee Mike Krajewski an accident.
The Forum reports that high pressure dislodged the equipment, causing it to smash Krajewski in the chest and abs, at about 3:30 p.m. Saturday.
A Halliburton spokeswoman said in an email to the Williston Herald that Krajewski's co-workers are saddened by the news.
Tara Mullee-Agard says the company is working with local authorities as they investigate. A second man also was injured in the incident.
The Occupational Health and Safety Administration began investigating the site Tuesday.