Five men were severely injured when their ice shanty exploded on Lake of the Woods in northern Minnesota over the weekend. According to the Duluth News Tribune, a propane tank exploded in their fish house, blowing out the windows and burning the structure.

Luckily the health status of three of the men has improved from critical condition. One of the anglers, William Huotari of Fargo, North Dakota remains in critical condition at a hospital in Duluth, according to the newspaper.

It is unclear how or why the propane tank exploded and the Minnesota State Fire Marshal’s office is still investigating the case. However, authorities believe the explosion was an accident.