The airborne particles put off by low-cost 3-D printers may be harmful to human health, U.S. researchers warned in a study published in the November issue of the journal Atmospheric Environment.

Consumer-level 3-D printers are growing in popularity, increasingly sold without any kind of filtration device or even so much as a warning that the printers spit out a large quantity of ultra-fine particles (UFPs) smaller than 100 nanometers in size.

That's due to the process used to melt-down and deposit thermoplastic in a programmed order, creating virtually any shape of object one can imagine. It's called thermoplastic extrusion and deposition, and researchers at the Illinois Institute of Technology wanted to know whether those particles it generates might be affecting people in unexpected ways.

"Other studies have shown that exposure to fumes from thermal decomposition of other thermoplastics, such as polytetrafluoroethylene (PTFE), is also acutely toxic to mammals, including humans," they wrote. "Moreover, ultrafine particles (UFPs: particles less than 100 nm) may be of particular importance for toxicity of fumes emitted from melting of some thermoplastics.

To measure the UFPs, researchers locked several identical 3-D printers in a non-ventilated room and ran them for 20-25 minutes at various temperatures and with different types of thermoplastic stock. Then they took samples from the air during and after the printing jobs were run and discovered that the printers were ejecting up 200 billion UFPs per minute with high-heat thermoplastic stock, and up to 20 billion with lower-heat stock.

"These results suggests caution should be used when operating some commercially available 3D printers in unvented or inadequately filtered indoor environments," they concluded. "Additionally, more controlled experiments should be conducted to more fundamentally evaluate aerosol emissions from a wider range of desktop 3D printers and feedstocks."