Most compressor stations are fuelled by a portion of the natural gas flowing through the station, although in some areas, all or some of the units may be electrically powered primarily for environmental or security reasons. All compressor stations are also equipped with emergency shutdown systems that can detect abnormal conditions such as an unanticipated pressure drop or natural gas leakage. These systems are designed to automatically shut down the engines, isolate and vent the affected piping, and direct the natural gas flow from the main part of the station.