This study is to survey the efficiencies of oil mist collector to remove the bacterial bioaerosols emitted from tunnel type computer numerical control (CNC) machine using metalworking fluids. Bacterial bioaerosols near the CNC machine were collected by MAS-100. The colonies were identified using API identification kit. The air flow rate was measured at the vent of the oil mist collector, and the particle concentrations were determined by the dual-channel direct-reading dust meter.

The bacterial concentrations in the tunnel type CNC machine working environment were lower than 1,500 CFU/m₃, the indoor air quality standards regulated by Taiwan EPA. The removal efficiencies of bacterial bioaerosols were 21.2% and 12.8% at the discharge port of the tunnel and in front of the closed door, respectively. Staphylococcus hominis was found to be the dominant identified strains. After oil mist collector turned on, particulate matter size in range of 2.5~5.0μm concentrationswere decreased from 76,256±34,743 #/L to 1,014±362 #/L and from 11,534±9,784 #/L to 150±50 #/L for particulate matter size larger than 5.0μm.

The oil mist collector could not only remove the oil mist but also decrease the bacteria bioaerosols. Therefore, the concentrations of bacteria bioaerosols emitted from tunnel type CNC and in metalworking workplace were lower than those of outdoors.