Safe means different things to different people. I don't know your duty cycle but I wouldn't consider over 85-90% duty cycle safe. Changes in ambient temperature or pressure from the conditions on the day it was tuned can lead to the ECU demanding more or less fuel at the same rpm and load. With many injectors roughly 85% DC can be the threshold beyond which the injectors don't close before being energized to be reopened. They are therefore always open and no additional fuel can be added if longer opening times are requested by the ECU. This can lean out a mixture at high RPMs and loads.