Newly published documents show oil on board a train that exploded in Casselton, North Dakota, contained high levels of flammable and toxic chemicals not found in other types of oil. DeSmogBlog reports the company due to receive the cargo had a special permit noting the oil contained high levels of volatile organic compounds. The report comes after federal transportation officials issued a warning about the oil, which comes from the Bakken shale reserve that stretches under North Dakota and Montana, saying it may be more flammable than other types of oil. The explosion in North Dakota forced the evacuation of a small town. A previous train derailment involving Bakken shale oil killed 47 people in Quebec.