14.3 Five-Location Obstruction Examination, Evidence, and Required Follow-Up

Define the investigation scope from the actual edition

An obstruction investigation follows evidence or conditions requiring examination beyond a routine assessment. NFPA 25 (2023), 14.3.2.2, identifies five minimum examination locations. The older four-category list of valve, riser, cross main, and branch line is not the current examination-reference list. Keep the investigation separate from the more flexible internal-assessment method under 14.2.

The five locations are the system or water-control valve where provided; the most remote end of the remote cross main; a branch line near the most remote line at its cross-main connection; that branch-line area at its remote end; and branch piping directly connected to the most remote low-point drain. Use the actual drawings and field arrangement to identify these locations. A convenient opening beside the riser is not automatically equivalent to a remote location.

These are minimum points, not a guarantee that five clean photographs establish every unexamined segment is clear. Extend the examination as needed to determine the extent and severity indicated by the findings. The exact access method and any permissible alternative nondestructive examination must be capable of addressing the condition and documented limitations.

Prepare for opening and evidence collection

Review the triggering event, previous findings, supply history, system drawings, and the operating configuration. Identify the protection affected by isolation and coordinate the impairment with the responsible owner/coordinator. Prepare safe drainage, access, replacement components, appropriate tools, and a restoration plan before dismantling. Confirm stored pressure is relieved through the approved method. Do not remove a cap simply because a distant gauge reads zero.

Control foreign-material entry during the investigation. Keep clean components and tools protected, use suitable temporary closures, and account for loose parts. Photograph each location before disturbing deposits where feasible. Record material distribution and appearance, approximate size, looseness, and whether it can migrate toward smaller openings. A ruler or other safe scale reference helps interpretation; a photograph without system/location identification is weak evidence.

Interpret deposits without inventing acceptance limits

NFPA 25 does not provide a universal deposit-thickness or percentage-area allowance that clears every pipe. The same fragment that is minor in a large main can obstruct a sprinkler orifice. Evaluate the amount, mobility, size, location, and connected openings. Do not scrape a deposit away and then report the original condition as clear merely because the final photograph looks clean.

Tubercules or slime found during investigation must be tested for indications of MIC. Arrange qualified analysis and follow the receiving laboratory's instructions for sampling, containers, preservation, and transport. There is no single mandatory twenty-four-hour/chilled/air-free protocol applying to every possible analysis. Do not add acid, bleach, or other chemicals to an unknown deposit to identify it by smell. Odor and color alone are not a definitive microbiological diagnosis.

When the finding requires complete flushing

Under 14.3.3, if the investigation indicates sufficient material to obstruct pipe or sprinklers, qualified personnel must conduct a complete flushing program. Merely expanding the investigation is not the complete required response. Establish the affected scope and suitable corrective method, manage protection, and coordinate the actual flushing or other necessary repairs. A brief main-drain run does not prove that every affected branch has been cleaned.

If the condition remains uncorrected or can continue to cause obstruction despite prior flushing, 14.3.2.1 requires the applicable five-year examination. Correcting the current blockage without controlling its source can allow recurrence. Review intake protection, supply repairs, corrosion conditions, drainage, and any design-required nitrogen supply. Preserve the ongoing examination and maintenance requirements in the owner's records.

Verify repair and restoration

Reassemble opened locations with appropriate components and instructions, complete required post-work tests, and check leaks and valve positions. Restore normal water/gas supply, QOD and other accessories, alarms, and monitoring as applicable. Remove impairment controls only after restoration has actually been confirmed. Record any remaining uncertainty as an open limitation requiring resolution rather than declaring a blanket pass.

The final report should connect trigger, locations, method, observations, laboratory findings, affected extent, correction, retest, and restored status. Identify who received notice and what follow-up remains. That chain of evidence makes the investigation useful for both immediate protection and future comparison.

Source checked October 19, 2026: NFPA 25 (2023), 14.3.2 through 14.3.4 and corresponding Annex A explanations.