When a well is drilled, cuttings of the rock and any gases that are within its pore volume are released and transported to the surface by the drilling mud. The gases, especially methane, have been responsible for catastrophic events on drilling rigs in the past when sudden outgassing occurred. For such cases, recommendations were developed and Governmental Authorities enacted laws for operations with combustible gases. These procedures led to the definition of safety areas around the zones where a gaseous mixture can explode, so-called Ex-Zones. The problem is that the dimensioning is only based on analytical models. The thesis does not put the correctness of the calculations into question, but wants to point out the limitations that are arising from lack of proper boundary conditions for these models. For this reason field tests were performed for measuring methane concentrations at several locations on a drilling rig. The data from gas sensors and from an anemometer was stored. Afterwards simulation studies were performed simulating the release of gas during drilling operations. The results show conspicuously that only calm wind conditions can lead to a dangerous methane concentration. So the very costly venture of the implementation of safety areas is only important in a limited area above and beside a gaseous source, and certainly not below. Considering all investigated facts, a modification of an Ex-zone plan for a drilling rig is suggested as a result of this work.