Popcorn lung and its association with diacetyl is a known phenomenon in workplace exposure scenarios, where people have large amounts of continuous exposure to high levels. We're not aware of any incidences of lung tissue scarring—that is, popcorn lung—occurring with vaping products. I think that's it for now.
The one other thing I'd point out is that even in the absence of a prohibition against that substance here, vaping products are subject to the Consumer Product Safety Act, which contains a general prohibition against the sale of anything that's a danger to human health and safety, an unreasonable hazard. If the evidence comes out that makes us think, yes, this is unreasonably hazardous in these products, the prohibition would be there to do it, and we can make regulations under either of the acts.