> It would be nice to know if this is something that compounds over time or if it is just the high concentration of the chemical that is affecting the people being reported on.

I think the science is not settled yet, which is why they are having a hard time making an exposure rule, but:

"NIOSH noted that five of six current employees who worked in the quality control room popping nearly 100 bags of product in microwave ovens per shift suffered airway obstruction despite relatively low full shift exposure to butter flavoring vapors."

http://www.gpo.gov/fdsys/pkg/FR-2009-01-21/pdf/E9-1125.pdf

From what I read about it seems like a cumulative hazard with no known safe level, every exposure does some damage. So I would install ventilation, or just buy a gas mask (they are not expensive, you can get them at a hardware store, probably cheaper than a ventilation system).