An arc flash detection system includes a sensor for determining and responding to the presence of an arc flash condition in electrical equipment by detecting a pressure rise, rate of pressure rise and/or ultraviolet radiation characteristic of an arc flash, and generating a signal in response thereto; and processing means responsive to said signal for operating a protective system to de-energize the electrical equipment within a period of time of sufficiently short duration to prevent a pressure wave from the arc flash from causing unacceptable darn age to equipment or personnel.