Several issues here.

First K2R works very well to remove oil from balsa, but it also contains dry cleaning fluid that will dissolve your liver over time, so work with it in a well ventilated area. Outside is best. It is not flammable. However acetone, while not particularly toxic, is highly flammable, so be careful to avoid any area where sparks can occur. The same applies to epoxy diluted with denatured alcohol. It can flash too.

Remember also that acetone dissolves CA glue, so if your model was CA'd together, you can seriously weaken joints by soaking it with acetone.