On the morning of Thursday, April 26th, an asphalt tank at the Husky Energy refinery exploded. Shockwaves from the location reverberated more than 15 miles away, as people in surrounding areas reported that it felt as though an earthquake was moving through the area.
An evacuation order was put into place and stayed in effect until the morning of Friday, April 27th, due to the enormous amount of toxic smoke that was generated by the explosion and subsequent fires. The evacuation zone covered nearly 72 square miles, most of which was located south of the refinery. This included all 27,000 residents of Superior, as well as roughly 13,000 people in the surrounding area.
Duluth was not subject to the evacuation order, but residents who suffer from health problems were encouraged to stay indoors for Thursday night (and possibly Friday, depending on the severity of their conditions).
The raging fires that followed the explosion could not all be immediately put out due to the high-intensity nature of asphalt fires. That raged until nearly 7 p.m., with the potential for later re-ignition due to the composition of the combustion materials.
Due to two projects that were in progress at the refinery, there were more than 500 people on-site at the refinery when the blast occurred. Eleven people were injured in the blast, and the long-term health effects for those exposed (or potentially exposed) to the toxic smoke are yet to be determined.
The cause of the explosion is not yet known, and Husky Energy has simply issued a statement saying that they are looking into potential sources of the blast.