By Jonathan R. Hart, PE
With many businesses rethinking how their office spaces will be utilized post-pandemic, a significant number will likely undergo renovations or redesigns. Add this to regular tenant fit outs, including shell space in newly constructed buildings, and there are sure to be thousands of existing sprinkler systems requiring modifications to adequately protect redesigned spaces. This often raises the question as to what extent the sprinkler system must be brought up to date with the latest standard, whether the system needs to be recalculated, and how extensive the testing of the modified system must be. Fortunately, the 2019 edition of NFPA 13, Standard for the Installation of Sprinkler Systems dedicated a chapter to the requirements for these instances for the first time and that information will carry over to the soon-to-be-issued 2022 edition.
Change Of Use/Occupancy
For the purpose of this discussion, we will focus on situations where the use or occupancy classification of the space is not being changed. Where that is the case a more complex analysis is likely required to determine the impact of changes to design densities, areas of operation, and several other possible changes. NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems places responsibility on the owner for ensuring an evaluation be conducted in these instances, many of which go beyond the reconfiguration of office space where the space protected is likely to remain a light hazard occupancy.
When a building is undergoing a renovation or a remodel of its space the removal or addition of walls, partitions, and ceilings can negatively impact the effectiveness of the originally designed sprinkler system. In these instances, numerous sprinklers must often be relocated or added in order to appropriately protect the reconfigured space.
This does not necessarily mean that the entire system must be reevaluated to ensure complete compliance with the latest edition of the standards. In fact, portions of the existing system that are not subject to the modifications can be considered previously approved under the retroactivity clause of NFPA 13, Standard for the Installation of Sprinkler Systems and do not need to be evaluated. Whenever additions or modifications are made to an existing system, enough of the existing system must be indicated on the plans to make all conditions clear for the AHJ to evaluate. This means that one of the first steps taken in these instances should be to gather as much of the existing plans and calculations, as is available. A more complex analysis might be required for the entire system if the original design basis cannot be confirmed.
While some have argued that minor modifications should not impact the system demand significantly enough to require calculations, NFPA 13 does require calculations be provided to verify that the system design flow rate will be achieved. Previous editions of the standard included an annex note indicating that it was not the intent to require a full hydraulic analysis of the existing sprinkler system, in addition to the new sprinkler layout. This note has been removed in recent editions. This still does not necessarily require a full set of hydraulic calculations particularly if the modifications are made in a part of the system that is not the most hydraulically demanding. In this case the modified portion of the system can be hydraulically calculated back to the branch line or riser to the point where original calculations are used to show that the design flow rate can be met. This is not entirely clear in reading the standard especially without the previous annex note to point to so it is certainly worth checking with the local AHJ to determine what they will accept for these instances.
Newly installed sprinkler systems must be hydrostatically tested to check for leaks at a pressure of at least 200 psi (14 bar) for a period of at least 2 hours. When existing systems are modified such that the work affects less than 20 sprinklers, the system only requires testing at the system working pressure. Where the modification affects more than 20 sprinklers, that portion of the system must be isolated and tested at 200 psi (14 bar) for 2 hours. If the new work cannot be isolated, the testing can be done at system working pressure even if the modifications involved more than 20 sprinklers. In general, existing portions of the system do not need to be subjected to a new hydrostatic test.
Striking A Balance
Many buildings are routinely undergoing changes that can impact the fire sprinkler system and require modification of the system to adequately protect the space as it evolves. The provisions for existing system modifications in NFPA 13 are intended to ensure that the space has adequate coverage, the system demand can still be met, and the workmanship of the job has been completed well enough. This is meant to strike the appropriate balance between ensuring that the changes are not simply ignored, not throwing the entire latest standard out, and saying everything must be brought up to those requirements.
Hart is a technical lead and principal fire protection engineer for the National Fire Protection Association (NFPA). This article originally appeared on the NFPA blog.
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