Assessing the level of heat hazard in rock mass. Measurements of virgin rock temperature were made in 89 active workings of collieries located in the area of Katowicki Holding Węglowy. Experimental method – in situ measurements, the results of the measurements are developed with the least square method. Using maps of the coal seams in the collieries, coordinates ( x , y , z ) of measurement points were determined, and then, by utilizing a surface map, the geodetic height of the physical surface over the measurement points was determined. The next stage was to analyse geological cross-sections; the thickness of stratigraphic layers i.e. overburden, carboniferous rocks and the total thickness of the coal seams located above the measurement points was determined. Coefficients characterising heat transport in the aforementioned types of rock were calculated using the least square method. By re-analysing geological cross-sections we determined the thickness of the previously mentioned stratigraphic layers for the locations, where rock temperature was to be determined. Virgin rock temperature was calculated for five levels in approximately 200 locations of Katowicki Holding Węglowy. Using these locations, isotherm maps of virgin rock temperatures in the collieries of Katowicki Holding Węglowy for the following levels were prepared: − 450 m, − 550 m, − 650 m, − 750 m and − 850 m. Preparing climate forecasts for the collieries of Katowicki Holding Węglowy. Developing a method to determine rock temperature in a point which cannot be reached, when values of the temperature in other points are known.