I've read that they emit toxic nanoparticles: http://www.sciencedirect.com/science...52231013005086

PLA is probably better than ABS in this regard, but PLA isn't quite as benign as people tend to assume. Apparently it is known to mimic estrogen, which can do all sorts of strange things to people. http://www.motherjones.com/environme...n-plastics-bpa

I'd say yes - ventilate.

Andrew Werby
www.computersculpture.com