Knox FDC Plugs The locking Knox® FDC plug was developed to protect fire sprinkler connections from accidental damage, vandalism and physical attack. Installation of a locking FDC cap ensures sprinkler reliability and building safety by preventing foreign objects from entering the sprinkler system. The Knox FDC is a 2.5 inch stainless steel male plug available in National Standard Thread and several other thread sizes and diameters. Locking 4 inch or 5 inch Storz caps made of hard-anodized aluminum are also available. The locking caps are easily and quickly removed during an emergency with a Knox Keywrench. The Keywrench engages a lock on the cap that is exclusive to the fire service nationwide. Keywrenches are controlled by each fire department that authorizes the program in their jurisdiction.   International Fire and Building Code The International Code Council has addressed the vulnerability of fire sprinkler systems via the Fire Department Connection (FDC). Effective January 1, 2003, the following language is included in both the International Building Code and International Fire Code: IBC 903.3.7.1 & IFC 912.3.1 Locking Fire Department Connection caps. The fire code official is authorized to require locking FDC caps on fire department connections for water-based fire protection systems where the responding fire department carries appropriate key wrenches for removal. Click to see FDC Caps