The intention of this article is to compare the containment performance of a Type II microbiological safety cabinet (MSC) confronted with the simultaneous generation of a saline nanoparticle aerosol and a tracer gas (SF6). The back dissemination coefficient, defined as the ratio of the pollutant concentration measured outside the enclosure to the pollutant flow rate emitted inside the enclosure, is calculated in order to quantify the level of protection of each airborne contaminant tested for three enclosure operating configurations: an initial configuration (without perturbations), a configuration exposing a dummy in front of the enclosure (simulation of an operator), and a configuration employing the movement of a plate in front of the enclosure (simulation of human movement). Based on the results of this study, we observed that nanoparticulate and gaseous behaviours are strongly correlated, thus showing the predominance of air-driven transport over particle-specific behaviour. The average level of protection afforded by the MSC was found systematically slightly higher for the nanoaerosol than for the gas in the studied configurations (emission properties of the source, operating conditions, and measurement protocols). This improved protection efficiency, however, cannot be considered as a warrant of protection for operators since operating condition and ventilation parameters are still more influential on the containment than the pollutant nature (i.e. nanoaerosol or gas).