preparatory stage for the construction of a ventilated crawl space in an old brick building against dangerous radon gas - concept

activity aerated air antiradon barrier brick building cancer casting concept concepts concrete construction contamination crawl danger dangerous digging excavation feature floor flooring foundation gas home ideas image industry lung natural old paving poisonous pollution preparatory protection radiation radioactive radioactivity radon risk safe security site soil space stage stratification stratified test ventilated ventilation wall