For even safer working, particularly in areas where there are stringent safety requirements such as refineries, chemical plants and industrial systems with a risk of explosion. The gas concentration of the suction air and the ambient air is continuously measured and evaluated by means of two sensors. A visual and audible signal is output when an advance warning stage is reached. The vehicle is shut down completely when the main alarm threshold is reached. All inflammable gases and hydrogen are analysed. A hand-held measuring instrument and charging station are also included.