A WVHA decree of March 31, 1942 established a minimum working day of eleven hours in all concentration camps. At Auschwitz, labor was one of the means used to destroy prisoners. They labored in various sectors of the economy. Initially, they worked at building the camp: leveling the ground, erecting new blocks and buildings, laying roads, and digging drainage ditches. Later, the industries of the Third Reich made increasing use of cheap prisoner labor. The pace of the work, the starvation rations of food, and constant beatings and abuse exacerbated the death rate. The German IG Farbenindustrie cartel, which built the Buna-Werke synthetic rubber and fuel factory at Monowice near Oswiecim, had priority in obtaining prisoner labor. The majority of the Auschwitz sub-camps were located near the mills, mines, and factories of Silesia. Prisoners dug coal, produced armaments and chemicals, and built and expanded industrial plants.