**3. Results**


Temperature, relative humidity, and air velocity were determined to characterize the background environmental conditions of the prototyping room and the conditions near the 3D printer while it was printing, as shown in Table 2.

**Table 2.** Environmental characterization provided by the thermo-hygrometer: Air velocity, room temperature and relative humidity.


The CPC provided the particle number concentration, from 10 nm to >1000 nm, during the three tasks under study, in addition to the background measurement. Table 3 indicates the mean particle number concentration for these four distinct periods. Additionally, Figure 1 illustrates how the concentration of this airborne particle changed over time during the trial.

**Table 3.** Results provided by the CPC.


**Figure 1.** Number particle concentration (#/cm3) over time measured by the CPC.

The SMPS allowed us to better understand the potential exposure to smaller particles, by providing the size distributions from 10 to 420 nm. The corresponding results are presented in Table 4 and Figure 2.


**Table 4.** Results provided by the SMPS: Mean particle number concentration (particles/cm3) by particle size.

(1) Geometric Standard Deviation.

**Figure 2.** Results provided by the SMPS: Mean particle number concentration (particles/cm3) by particle size range.
