Introduction: The high energy and temperature used for melting metals during additive manufacturing generate high numbers of fine (FP) and nanoparticles (NP), with significant time-dependent variations. To evaluate possible health risk, we investigated the time course of airborne FP and NP released during different phases of two selective laser melting processes as well as their environment boundaries (temperature t, humidity UR, mechanical ventilation MV). Materials and methods: FP were monitored by the aerosol particle counter LasairIII (Particle Measuring System, 0.3-25 μm). DiSCmini (Testo), was used for measuring number (n) and average diameter (δ) of NP (10-300 nm). t and UR were monitored through data logger 174-H (Testo). Results: The core of the printing phase entailed a slight but continuous increase of n and δ, and almost constant FP number, whereas the warm-up and cleaning without MV increased the n of released NP by +26% and +37%, respectively. Turning-on MV during cleaning and warm-up limited the increase of n (respectively -50% and +1% as compared to printing). At the end of printing, with no MV and no operating activities, there was a constant increase of n and decrease of δ (respectively +48% and –22% in 14 hours), suggesting the low deposition rate of generated NP, with a positive relationship between the n and UR. Conclusions: The phases and operators’ tasks as well as the environment boundaries have impact on the NP release and size. Analysing a wider spectrum of conditions and processes is necessary to characterize potential exposures and to suggest effective mitigation measures.