Most 3-D printers print with PLA filament (polylactic acid) which is made of corn starch. People are not affected by PLA fumes. I think this unfortunate couple may have printed with nylon filament (as in weedwhacker string) which I understand gives off noxious fumes and must be vented. Unfortunately these articles do a disservice to the entire maker movement by not telling us what this couple was doing.
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dailymail.co.uk: San Francisco Couple dies from Leaking 3D Printer
http://www.dailymail.co.uk/news/article-4167150/San-Francisco-couple-died-leaking-3-D-printer.html
Related: chicagotribune.com: 3D printer study drills down on potentially harmful emissions
http://www.chicagotribune.com/bluesky/originals/ct-3d-printer-emissions-health-risks-bsi-20160203-story.html