( CNN ) -- Crews in North Dakota were testing the air Tuesday morning for any dangerous fumes a day after two trains wrecked , sparking a large fire . The results of the tests will help determine when it is safe for residents to resume their routine activities . One of the trains was carrying crude oil , which sent dangerous smoke into the air , officials said . The incident occurred one mile west of Casselton , a town of 2,300 residents about 25 miles west of Fargo . Authorities issued an evacuation order , which was not mandatory , but `` strongly , strongly recommended , '' Cass County Sheriff Paul Laney told CNN . He estimated that 65 % of area residents heeded the call to leave their homes . There were no injuries in the wreck , and everyone is accounted for , Laney said . `` When you see the fireball and you see the damage and the aftermath , that 's amazing that nobody was hurt , '' he said . `` There were people inside their homes that could feel the heat from the explosion in their homes . '' Firefighters were forced to let the fire burn out . The extreme heat made it impossible for them to get close enough to the flames to battle the blaze . CNN 's Steve Almasy , Aaron Cooper and Carma Hassan contributed to this report .
Crews are testing the air near Casselton , North Dakota . They are testing for any toxic fumes . Score: 7