An anonymous reader writes: A new study by researchers in the Built Environment Research Group at the Illinois Institute of Technology shows that commercially available desktop 3D printers can have substantial emissions of potentially harmful nanosized particles in indoor air. Many desktop 3D printers rely on a process where a thermoplastic feedstock is heated, extruded through a small nozzle, and deposited onto a surface to build 3D objects. Similar processes have been shown to have significant aerosol emissions in other studies using a range of plastic feedstocks, but mostly in industrial environments. In this study, researchers measured ultrafine particle concentrations resulting from a popular commercially available desktop 3D printer using two different plastic feedstocks inside an office. Ultrafine particles (or UFPs) are small, nanosized particles less than 100 nanometers in diameter. Inhalation of UFPs may be important from a health perspective because they deposit efficiently in the lung and can even translocate to the brain. Estimates of emission rates of total UFPs in this study were high, ranging from about 20 billion particles per minute for a 3D printer utilizing a lower temperature polylactic acid (PLA) feedstock to about 200 billion particles per minute for the same type of 3D printer utilizing a higher temperature acrylonitrile butadiene styrene (ABS) feedstock. The emission rates were similar to those measured in previous studies of several other devices and indoor activities, including cooking on a gas or electric stove, burning scented candles, operating laser printers, or even burning a cigarette.