In late July the NFPA 13 Sprinkler System Discharge Technical Committee voted to pass a proposal allowing a higher C-factor for new dry pipe and preaction sprinkler systems that are maintained with nitrogen generators in place of air compressors in the next edition (2022) of NFPA 13. This C-factor allowance will only apply to new system installations and not apply retroactively to existing fire sprinkler systems.
The precedent for this action was the revision of the US Department of Defense Fire Code, the Unified Facilities Criteria (UFC 3-600-01) in April 2018 permitting a C-factor of 120 when nitrogen gas is used to maintain dry pipe and preaction sprinkler systems. There are a few more procedural steps required before this allowance becomes official, but the second (and final) draft of the revised NFPA 13 standard will be posted by January 21, 2021.
The updated C-factor table will look similar to the following:
|Piping Or Tube||C Value|
|Black Steel (dry systems)||100|
|Black Steel (wet systems)||120|
|Black Steel (dry systems) using nitrogen gas||120|
|Galvanized Steel (dry systems)||100|
|Galvanized Steel (wet systems)||120|
|Galvanized Steel (dry systems) using nitrogen gas||120|
The practical impact of this allowance is quite significant for fire protection engineers and sprinkler designers. A higher C-factor yields a lower coefficient of friction in hydraulic calculations for fire sprinkler systems. Incorporating nitrogen generators with new dry pipe and preaction sprinkler systems can potentially provide the following benefits:
The cost reduction from any one of the above benefits will more than offset the cost of a nitrogen generation system. By offering an incentive for nitrogen generators the NFPA clearly acknowledges the long-term system performance and reliability advantages that nitrogen generators provide by continuously maintaining an inerted atmosphere within the sprinkler piping. In their discussions, the committee differentiated nitrogen generators from nitrogen cylinders, concluding that nitrogen cylinders represent a finite and less reliable supply of nitrogen gas and therefore do not qualify for the higher C-factor.