There are five FPCON levels:
FPCON NORMAL: Applies when there is no discernible terrorist activity. Under these conditions, only a routine security posture, designed to defeat the criminal threat, is warranted. The minimum FPCON is NORMAL.
FPCON ALPHA: Applies when there is a general threat of possible terrorist threat activity against personnel and/or installations, the nature and extent of which is unpredictable, and circumstances do not justify full implementation of FPCON BRAVO measures. However, it may be necessary to implement certain measures from higher FPCONs resulting from intelligence received or as a deterrent. Commands must be capable of maintaining FPCON ALPHA measures indefinitely, with only limited impact on normal operations.
FPCON BRAVO: Applies when an increased or more predictable terrorist threat exists. Commanders must be capable of maintaining the measures of this FPCON for several weeks without causing undue hardship to personnel, substantially affecting operational capabilities, or aggravating relations with local authorities and members of the local civilian community.
FPCON CHARLIE: Applies when an incident occurs or intelligence indicates some form of terrorist action against personnel and/or facilities is imminent. Implementation of FPCON CHARLIE measures for more than a short period probably will create hardships for personnel and affect the peacetime activities of units and personnel.
FPCON DELTA: Implementation applies in the immediate area where a terrorist attack has occurred or when intelligence indicates terrorist action against a specific location is likely. Implementation of FPCON DELTA normally occurs for only limited periods of time over specific, localized areas. Commands cannot sustain FPCON DELTA for extended periods without causing significant hardships for personnel and substantial reductions in capability to perform normal peacetime missions.