The release of hazardous nanoparticulate matter in accidental situations was simulated in a specially designed 13-m(3) stainless steel airtight chamber, which allowed the dispersion analysis of airborne matter in a practically particle-free environment (less than 2 #/cm(3)) and in presence of background atmospheric aerosols. A fast recovering of the initial situation was achieved by means of a tandem HEPA-filtered air and deionized water system. Both unintended spilling of silica-based nanoparticulate powders and continuous emission of 100-nm SiO2 nanoparticles were used as aerosol generation events. The emission of airborne nanoparticles was analyzed in terms of particle number concentrations (PNC), size distributions and source strengths. The emission of nanoparticulate aerosols reached peak PNC for particles in the range from 5 nm to 1 mu m with source strengths about 10(8) #/h in a background-filled environment and 10(10) #/h in a practically particle-free atmosphere. No agglomeration was noticed for the released nanoparticles, suggesting that PNC was low enough to prevent coagulation and that particle diameters were over 80 nm. Results indicate that emitted matter was within the range of the most penetrating particle sizes and with source strengths similar to accidental scenarios. (C) 2014 Elsevier B.V. All rights reserved.