While there has not been extensive studies done as of yet, it is intuitive that the gas and particles released by the heating of plastics for 3D printing cannot be healthy. This is why it is best to have proper ventilation. You do not want to be printing overnight, every night, with the machine on your nightstand.
At SD3D we have been working closely with a university in order to get real data on the health effects of 3D printing. We happen to print as much as possible in an enclosed environment with filters on the outside of the exaust fans, which drastically reduces any harm that may come. While it will take more time to get final data, it is clear that standing over a print of Carbon Fiber ABS while it extrudes is not beneficial to your health.
A paper published in the journal Atmospheric Environment by the Illinois Institute of Technology measured the amount of harmful ultrafine particles (UFP) that desktop printers emit into the air. Materials brought back a UFP of 20-200 billion particles per minute. The study says these particulates will stay in your lungs, but the longterm effects are still not perfectly understood. Other than this study, most data is taken from studies not directly related to FDM printing.
We originally wanted to enclose our printer to keep the ambient air hot in order to prevent warping and delamination. This transformed into a device that moderates the temperature and can blow air out anywhere that is hotter than the average. This air is then blown out of the specific location of the printer through a small carbon filter. This not only helps to produce a clean print, but can reduce any amount of particulates that exist in the air during the print.
Since there are extensive patents that currently exist for enclosed printing devices, we had to get creative to make sure we are not breaking any intellectual property laws. A patent such as this is not only preventing 3rd parties from expanding the industry, but can also cause health problems by limiting the amount of proper precautions a user can take.