This is an evolving area, so venting outside is probably the safest option. Other people have pointed out that the two issues are 1) particulate matter addressed by the HEPA filter 2) volatile organic chemical fumes addressed by the active charcoal filter. Make sure you have both if you are running ABS or anything higher temperature.

You might check out the UL safety report. Look for the title "Managing Safety in Additive Manufacturing Facilities"