Kippenhahn diagram of a M_ini = 30 M_⊙ single star at solar metallicity with a He-C shell merger. The ⁴He mass fraction is shown as a function of the evolutionary time (τ) from central He depletion to the onset of core collapse (τ_CC). Hatched regions show the convection and overshoot. Helium is dredged downward by a stochastic convective zone, such that helium is burned into carbon via the 3α reaction in deeper layers. This results in anomalously high carbon in the stellar interior at core collapse.