A Minnesota prison has “resolved without incident” a situation involving about 100 inmates in one housing unit who would not return to their cells Sunday in what one former inmate there called an act of “self-preservation” amid dangerously high temperatures in the region.

The situation was “calm, peaceful and stable throughout the day,” a Department of Corrections spokesperson said in a statement, adding that “incarcerated individuals in the unit indicated dissatisfaction” because the understaffed facility had to limit inmates’ time out of their cells.

But advocates positioned outside of the Stillwater prison, some of whom have family members inside, said inmates are fed up with the excessive heat, lack of air conditioning and limited access to showers and ice during on and off lockdowns over the past two months.