BUTLER COUNTY — Law enforcement authorities had a long night and have ended their investigation and search for a man who allegedly had an assault rifle at a refinery in Butler County.

Just after 10:30 p.m. deputies responded to the HollyFrontier refinery in 1400 Block of Douglas Road in El Dorado. A contractor at the refinery reported seeing three men on the property and one was carrying an assault rifle, according to Sheriff Kelly Herzet.

Deputies set up a perimeter and helped evacuate over 600 employees and contractors. The Butler County swat team with help from Harvey County assisted at the scene, according to Herzet. In the midst of the search for the alleged suspects, a thunderstorm rolled through and delayed the search.

Deputies didn’t see anyone and officials locked the refinery down tight, according to Herzet. After an interview with the reporting party authorities gave the all clear at 5 a.m. There were no injuries reported.

HollyFrontier owns and operates refineries located in Kansas, Oklahoma, New Mexico, Wyoming and Utah and markets its refined products principally in the Southwest U.S., the Rocky Mountains extending into the Pacific Northwest and in other neighboring Plains states, according to the company web site.