Within this master thesis, the environmental conditions of three tunnel sites were investigated. Contract section “Wolf 2” was a deep tunnel. In section “Stein”, “Koralmbahn”, two shallow tunnels, “Lind West” and “Stein West”, were monitored. Section “Wolf 2” had a length of about 5.000 m, “Lind West” had 360 m and “Stein West” had 260 m. Three permanent measuring points for long-term measurements were installed in “Wolf 2”. The others, “Lind West” and “Stein West”, were equipped with two each. The measured data included airborne dust concentration, gases, temperature, air velocity, relative humidity and barometric pressure. Additionally the wall temperature, illumination level, sound pressure level and the velocity of vehicles were gauged. The vehicle speed was in the range of 20 km/h to 34 km/h. The air velocity fluctuated at all permanent measuring points around a constant average. Measuring point 1, “Wolf 2”, was the sole exception to that observation. The dust and gas concentrations were compared with the MAC (maximal allowable concentration). The permanent measuring points allowed the determination for the movement of fumes from face to portal. The fumes in “Wolf 2” needed approximately three hours. In “Lind West“ and “Stein West“ this took only some minutes. The gas concentrations of oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulphide (H2S), sulphur dioxide (SO2), nitrogen monoxide (NO), nitrogen dioxide (NO2), methane (CH4) and combustible gases (COMB/EX) were gauged. Oxygen was always at about 20,8 %. A high peak in the concentration of CO and NO was measured after blasting. All safety values of NO were met but the short term exposure value of CO was violated at “Wolf 2”, even after a ventilation of 15 minutes. The concentration of CO2 increased due to blasting and vehicles. The illumination level showed a strong dependence on the distance to a light source. It decreased rapidly within some meters. Differences in the illumination level were found for measurements at a sunny, “Wolf 2”, or cloudy day, section “Stein”. The sound pressure level got uncomfortably and even painfully high. The maximum measurable sound pressure level of the analyser, 130 dB, was insufficient to measure blasting. Temperature and wall temperature increased along the tunnel length from portal to face. The wall temperature decreased due to damp areas and increased close to lamps. Measurements taken near the portal were strongly affected by the weather conditions. Every underground used system must be able to resist the sometimes high dust concentrations. The concentrations of the gases CO, CO2, NO und NO2 should be monitored for the safety of the workers.