- The present paper introduces induced airflow as an effective means for removal of contaminants from underground enclosed spaces. The airflow is caused by natural convection in a vertical duct which absorbs solar irradiation outside the building. Experimental studies and three-dimensional numerical simulations have been performed in a scaled-down laboratory model. The experiments included temperature and velocity measurements and flow visualization. The results obtained from the simulations are fully supported by the experimental results, indicating that effective ventilation by the proposed method is achievable. For real-size structures, three-dimensional computer simulations have been performed using a standard k-epsilon turbulence model. The results yield a detailed flow field inside the enclosure for various configurations of the ducts and partitions. Rate of air change is calculated both for the whole enclosure, and for the regions above the floor where contaminants like radon tend to accumulate. By adjustment of openings in the basement, the ceiling may be cleared of contaminants as well. It is shown that a properly designed structure, even at low solar fluxes, can provide adequate ventilation of a real-size underground enclosure.