14.2 The Sixteen NFPA 25 (2023) Obstruction-Investigation Triggers

Sixteen conditions require attention in the 2023 edition

NFPA 25 (2023), 14.3.1, lists sixteen obstruction-investigation conditions. Do not rely on the older fourteen-condition count or wait for the next scheduled internal assessment when a trigger is present. The trigger establishes the need to investigate; it does not by itself identify the exact blockage location, require identical corrective work in every case, or prove that every pipe is completely obstructed.

Use the following paraphrased checklist with the actual standard. Record the condition, system or yard-main location, date, supporting evidence, and the responsible follow-up. Several triggers concern supply contamination or history rather than something visible at the riser. Coordination with the owner, water supplier, and other service personnel can therefore be essential.

1. Defective open-water pump intake. Damage or failure can allow material into a pump drawing from a lake, river, or other open source. Evaluate the intake condition and affected supply path.
2. Obstructive material discharged during routine water tests. Preserve useful observations and identify the test and outlet rather than treating all dirty-looking water as the same finding.
3. Foreign material in a fire pump, dry valve, or check valve. Material found during service can indicate contamination beyond that one component.
4. Foreign material in drain-test water or a plugged inspector's test connection. A restricted outlet can be evidence of a wider issue, not simply an inconvenient test valve.
5. Unknown material heard moving inside piping during draining, refill, or flow. Document the location and circumstances; do not assume every unusual sound is harmless trapped air.
6. Plugged sprinklers. Investigate the source and extent rather than replacing one plugged unit and automatically declaring the network clear.
7. Organic or inorganic material inside piping with obstruction potential. Size, mobility, and the openings it can reach matter as well as the amount.
8. Failure to flush yard piping or nearby public mains after installation or repairs. Construction and repair history can indicate introduced debris even before a local test reveals it.
9. A record of nearby broken public mains. Review relevant supply events with the owner or water authority and evaluate the connected system.
10. Abnormally frequent false dry-valve trips. Review operating history and causes; repeated flooding can introduce or move material.
11. Return to service after shutdown longer than one year. The trigger is not limited to a system known to have been completely drained.
12. Reason to suspect sodium silicate or highly corrosive flux in copper systems. Review material and service history; do not prescribe an improvised chemical treatment.
13. Raw water supplied through the FDC. The apparent success of emergency pumping does not eliminate possible introduced contamination.
14. Leakage caused by internal corrosion. Evaluate the affected piping and associated material; patching a leak does not demonstrate unobstructed service.
15. The specified increase in total dry/double-interlock-preaction water delivery time. Compare equivalent normal-gas-pressure conditions with original acceptance data as described below.
16. Failure to maintain nitrogen where the approved increased-C-value design depends on it. The provision addresses dry/preaction systems using C=120 and contains the stated preplanned-impairment exception.

Calculate the delivery-time trigger correctly

The 2023 provision uses a 25% increase in total water delivery time, or a five-second increase for portions protecting dwelling units. It does not use a universal fifty-percent trip-time increase. Time begins when the inspector's test connection is fully opened, and the comparison uses normal system gas pressure and the original acceptance result.

If the original delivery time is 40 seconds and a comparable current result is 52 seconds, the increase is (52−40)/40 × 100 = 30%. That reaches the 25% trigger. For a dwelling-unit portion with an original 35-second result and current 40-second result, the five-second increase reaches the specified dwelling-unit trigger even though the percentage increase is only about 14.3%.

Investigation is distinct from a routine schedule

A system assessed last month can still require investigation after obstructive material is found today. Conversely, an investigation finding must be evaluated through the applicable procedure; the trigger list is not a universal rule that every event requires wholesale pipe replacement. Establish extent, material, and actual system effect. Use the five-location examination requirements and permissible methods in 14.3.2, then apply the complete-flushing requirement when sufficient obstructive material is indicated.

Prevention and communication

Keep open pipe protected during construction/service, account for tools and temporary plugs, flush the applicable supply work, maintain intake protection and nitrogen arrangements, and preserve test/history records. Coordinate public-main repair information and raw-water FDC use with the responsible parties. These actions help prevent contamination and reveal triggers promptly.

Notify the owner of consequential findings and manage any actual impairment. Do not wait for a polished annual report while an obstructed or unavailable system remains untreated. Record the trigger, investigation scope, findings, correction, tests, and final status so a later reviewer can follow the complete decision.

Source checked October 19, 2026: NFPA 25 (2023), 14.3.1 through 14.3.4.