Dynamic systems that are subject to fast disturbances, parametrised by a disturbance vector d, undergo bifurcations for some values of the disturbance d. In this work we specifically examine those bifurcations which give rise to system trajectories that leave the domain of attraction of a desired system state. We derive equations which describe the manifold of bifurcation values (that is the manifold of disturbances d which cause the system trajectory to abandon the desired domain of attraction) and the corresponding normal vectors. The system of equations can then be used to find the smallest critical disturbance in physical, biological or other systems, or to robustly optimise design parameters of an engineered system.