A class B solar flare was the classification for a solar flare used by Starfleet.

In 2369, when the USS Enterprise-D was inside a Dyson sphere, there was a large magnetic disturbance on the surface of the sphere's star. This disturbance generated a class B solar flare with a magnitude of twelve. The Enterprise-D was protected from this solar flare by its shields. (TNG: "Relics")