  In this article, we investigate the dynamical robustness in a network of
relaxation oscillators. In particular, we consider a network of diffusively
coupled Van der Pol oscillators to explore the aging transition phenomena. Our
investigation reveals that the mechanism of aging transition in a network of
Van der Pol oscillator is quite different from that of typical sinusoidal
oscillators such as Stuart-Landau oscillators. Unlike sinusoidal oscillators,
the order parameter does not follow the second-order phase transition. Rather
we observe an abnormal phase transition of the order parameter due to sudden
unbounded trajectories at a critical point. We call it a dangerous aging
transition. We provide details bifurcation analysis of such abnormal phase
transition. We show that the boundary crisis of a limit-cycle oscillator is at
the helm of such a dangerous aging transition.
