I don't think there's enough testing to know those thresholds. As far as what I can tell there's more scientific studies that show as long as it's not combusted at 500+degrees PG, peg vg and.mct are no more harmful (maybe even less so) then terpenes themselves
Yeah but "no more harmful" isn't a very good argument in defense of TT, or any dilatant product or terpene for that matter. And if there aren't studies that show how it can be used safely, how can any company make any claims about their product at all?
I really don't think the argument that Future makes about terpenes being bad in concentrate is really relevant either. By that logic, why not turn on my car while I am smoking in my garage? It'll all kill me one way or another... In all seriousness, it would just suggest that maybe terpenes shouldn't be considered so safe either.