How an in-service underwater rover inspection works
An interior inspection of a fire protection water tank is done one of two ways. Out of service means the tank is drained, opened, and looked at empty. In service means the tank stays full and the interior is looked at under water. An underwater rover inspection is the in-service method: a remotely operated vehicle goes into the water, and a pilot outside the tank flies it and records what it sees.
The tank is not drained, emptied, or refilled for the inspection. That is the main reason owners choose it. Draining a fire water tank takes the building’s fire protection water supply out of service, and the tank has to be refilled before that supply is back. An in-service rover inspection avoids taking the supply out of service. The tank keeps protecting the building while the rover works.
The pilot flies the rover over the walls, the floor, and the fittings, and records the conditions the interior shows. FLOW does this work in service only. We do not offer a drained inspection as an alternative. When the tank or the AHJ calls for one, we refer it to a licensed partner firm.
What the pilot looks for and records
NFPA 25 Chapter 9 sets out what an interior inspection is looking for. The standard’s checklist covers pitting, corrosion, spalling, rot, other forms of deterioration, waste materials and debris, aquatic growth, and local or general failure of the interior coating. The 2017 text also calls for looking at the heating system and its piping, and at the anti-vortex plate for deterioration or blockage.
On a FLOW rover inspection, the pilot records what the interior shows: silt and sediment conditions, coating loss, corrosion, and debris on the walls, floor, and fittings. Those findings are the reason for the inspection. Debris and sediment on the floor are the material a fire pump or the tank outlet ingests during a fire. A failed coating leaves bare steel exposed, which is how a tank on the 5-year clock becomes a 3-year problem.
Keep the record of the inspection with the rest of the NFPA 25 records for the property. The AHJ will ask for the date and the findings, not just the invoice. If you need to know what documentation your inspection will include, ask when you request a quote.
Silt and sediment: documented by the rover, removed by others
Sediment matters twice in a fire water tank. It hides the floor from the inspector, and it is what the outlet draws in when the tank is called on. Where the interior inspection is made by underwater evaluation, the 2017 text of NFPA 25 calls for silt to be removed from the tank floor first.
FLOW does not remove silt or sediment. If silt has to come out before an underwater inspection, it is removed by others before the visit. The rover inspection documents the silt and sediment conditions it finds. If the sediment is heavy enough that the floor cannot be seen through the water, a drained inspection may be the right call, and FLOW refers that to a licensed partner firm.
Where the rover inspection fits in the NFPA 25 schedule
The rover inspection is how a tank meets its interior interval without being drained. NFPA 25 puts the interior inspection of steel tanks without corrosion protection at every 3 years, and the interior of all other tanks at every 5 years. That includes coated or lined steel, concrete, wood, and coated fabric tanks. The clock is set by the tank material and its corrosion protection, not its size or age.
The section number depends on the edition: 9.2.6.1.1 and 9.2.6.1.2 in the 2014 edition, and 9.2.5.1.1 and 9.2.5.1.2 in the 2017 edition. Virginia enforces the 2020 edition through the 2021 Statewide Fire Prevention Code, which incorporates the 2021 International Fire Code; its Chapter 80 lists NFPA 25-20. For the 2020 edition, confirm the section number in your copy using Table 9.1.1.2 (“Summary of Water Storage Tank Inspection, Testing, and Maintenance”). Confirm the adopted edition with your AHJ before you quote a date.
The interval runs from the last documented interior inspection. If there is no record, assume the tank is overdue and schedule one.
The full table by tank type and edition is on our NFPA 25 tank interior requirements: 3-year vs 5-year page. The short-cycle level, temperature, and exterior checks are on the fire water tank inspection overview.
What the AHJ may accept
The property owner is responsible for inspection, testing, and maintenance of a private fire protection water tank under NFPA 25. The AHJ, usually the local fire marshal in Virginia, enforces the adopted edition and decides what it accepts, including whether an in-service rover inspection meets the interior requirement for a particular tank.
Ask before you schedule, not after. Tell the AHJ the tank material, whether it has interior corrosion protection, the date of the last interior inspection, and that you plan an in-service underwater inspection. If the last report showed coating failure, ask whether the AHJ wants the tank treated as unprotected, and whether it wants a drained inspection instead.
FLOW performs the in-service inspection visit. We are not the AHJ, we do not issue engineering stamps, and we do not sign a tank back into service.
When the tank has to be drained instead
An in-service inspection is not the right method for every tank. A drained, out-of-service inspection may be the right call when sediment has to come out, when the inspector cannot see the floor through the water, or when a coating has failed and the steel needs closer testing.
When a steel tank shows pitting, corrosion, or coating failure, NFPA 25 Chapter 9 calls for further evaluation on a drained tank. Industry practice for that step includes coating adhesion testing, dry-film thickness, and ultrasonic thickness readings. That is qualified tank inspector work. FLOW does not perform it, and FLOW does not repair coatings.
FLOW does not drain, empty, or refill a tank for inspection and does no out-of-service tank visits. We refer drained, out-of-service inspections to a licensed partner firm. When a job needs a license FLOW does not hold, we route it to a licensed fire protection partner firm.
| Work | Who does it |
|---|---|
| In-service interior inspection with an underwater rover flown by a pilot | FLOW |
| Recording silt and sediment conditions, coating loss, corrosion, and debris | FLOW |
| Silt or sediment removal before an underwater inspection | Others, before the visit |
| Draining, emptying, or refilling the tank for inspection | Not FLOW — licensed partner firm |
| Drained, out-of-service interior inspection | Not FLOW — licensed partner firm |
| Coating repair, adhesion, dry-film, or ultrasonic thickness testing | Not FLOW — licensed partner firm |
| Engineering stamp or AMPP CCI certified report | Not FLOW |
| Accepting the inspection and enforcing the adopted edition | The AHJ |
Before you schedule an underwater tank inspection
Last interior inspection — find the date and the report. The interval runs from that date, and the last findings tell you what to look at first.
Tank material and protection — steel without corrosion protection is on the 3-year clock; everything else is on the 5-year clock. Confirm the row with your AHJ.
AHJ acceptance — confirm the adopted edition and that the AHJ will accept an in-service underwater inspection for this tank.
Silt — if silt has to be removed from the floor first, arrange that with others before the visit. FLOW does not remove silt.
Your tank — when you request a quote, tell us what the tank is, what it is made of, and where it is, so we can tell you whether an in-service rover inspection suits it.