of SPBsg variables. The presence of g-mode pulsations in B-type post-main sequence stars has been explained by a partial reflection of some modes at an intermediate convective zone (ICZ) related to the hydrogen-burning shell or at a chemical gradient zone surrounding the radiative core.

However, all studies of these objects published so far are based on the assumption that HD 163899 has not reached the phase of core helium ignition, i.e., it is in the phase of shell hydrogen burning. This assumption might not necessary be fulfilled, because the blue loop can reach temperatures of early B spectral types. In this paper we calculate models which undergo core helium burning on the blue loop and compare them with models in the hydrogen shell burning phase.

The structure of the paper is as follows. In Section \[domains\], we present the new instability domains which include pulsational instability on the blue loops. The effects of opacity, metallicity, overshooting, element diffusion and mass loss on the pulsational instability areas are studied. Propagation diagrams and properties of instability parameter and kinetic energy of modes for representative models are described in Section \[models\]. In Section \[identification\] we construct photometric diagnostic diagrams for the B-type supergiant 