There is no such thing as a 3D printer that doesn't emit concerning microparticles into the air, according to Rodney Weber's groundbreaking study about the dangers of 3D printing. Even industrial models that appear sealed put out measurable particles. 

But Weber warns us not to be too alarmed. The true danger is that the industry is currently unregulated, but the particles from 3D printer's aren't any different from the ones already floating around in the air.

Weber is a professor in the School of Earth and Atmospheric Sciences.