Even when using an enclosed 3D printer, heated filaments can release toxic fumes into the air. For this reason, the Sunderland Foundation Innovation Lab only uses PLA filament due to its reputation as a safer filament.
3D printers work by melting layers of filament on a heated bed for better adhesion. Consequently, temperatures can exceed 100°+C (200°+F)! Touching parts of the printer can result in serious burns. Interfering with printer operation can also affect the printer's calibration.
The 3D printer mindlessly prints whatever it was programmed to do. It can't sense obstacles and will pinch (or burn) if touched.
Watch the heat! 3D printers operate at high temperatures and should be monitored, especially at home.