Could non-supernova carbon, oxygen, or silicon flashes be observed?
There is also something called a "giant eruption", like eta Carinae, which is a type of "failed supernova" because it didn't destroy the star.  It is not known what causes giant eruptions, but perhaps one thing to think about is a flash of the type you mention.  Giant eruptions certainly are visible, eta Car got quite bright when it blew off much of its envelope.