FERC Part 12 Dam Safety Inspections: The Diver's Role
By Ray Whitfield, ADCI-certified commercial dive supervisor. Reviewed by Dana Whitcombe, technical reviewer.
Cathodic Protection & Anodes | Offshore & Subsea Diving I remember a Thursday morning on a run-of-river dam on the Susquehanna. The plant operator handed me a roll of FERC Part 12 drawings and said, 'You'll be in the plunge pool today. Good luck.' That's as much direction as you get sometimes. I've been in this work since the mid-1990s. FERC Part 12 is the Federal Energy Regulatory Commission's independent consultant inspection rule for licensed hydro projects. Under 18 CFR 12.30, it applies when a dam is over 10 metres -- call it 32.8 feet -- tall, or when the impoundment crosses the threshold spelled out in the rule. A Part 12 inspection means a formal look at the whole project, including everything under the waterline. The engineer signs the report. The diver hands him the facts. What I want to put down here is what that role actually looks like from the bottom of a stilling basin, and what it takes to do it right.
What Part 12 actually asks from divers
Part 12 is about safety and continued operation. The independent consultant looks at the project, judges its condition, and files a report. A big part of that report depends on knowing what the trash racks, gate slots, concrete faces, stilling basin aprons, and the dam toe look like below the surface. That's the diver's piece. We are an extension of the consultant's eyes. We do not make structural judgments, but we give the engineer something solid to judge. We measure cracks, sound questionable concrete, pull sediment samples, and document rebar exposure. We mark locations on a survey grid and annotate every video frame. On bigger jobs we use an ROV for pre-scouting, but you still need a diver's hand on the structure to know if that crack is a hairline or a separation you can fit a caliper in. The team's certification has to hold up. Commercial diving is covered under OSHA's 29 CFR 1910 Subpart T. ADCI sets consensus standards that most owners and many consultants require. But ADCI is an industry body, not a regulator. A recreational scuba certification means nothing here. I've trained enough divers to know the difference. The consultants know it too.
What we're actually looking for
The checklist shifts with water level, the age of the dam, and what's upstream. But the themes are the same. I'm looking for scour at the toe from years of discharge. I'm looking for debris pile-ups on the trash racks that choke an intake. I'm looking for spalled concrete, exposed aggregate, rusted rebar. I'm also looking for movement: differential settlement between concrete monoliths, tilted gate guides, worn seals. In one old powerhouse on the Tennessee River, we found a void behind a gate guide that showed as a hairline crack on the surface. Put a probe in and you could feel the space behind it. That's the difference between a surface picture and a subsurface understanding. An ROV shows you the video; the diver's hand tells you if it's a hollow sound. We use old-school tools alongside the new. A steel sounding rod works as well today as in the 1980s. A four-pound hammer sinks fast, so you hang on to it and let the sound tell you something about the concrete. We carry tape, a waterproof camera, and on large jobs a small sonar unit. The point is not gear. The point is getting close enough to see what's actually there.
The hazard that'll kill you: differential pressure
Delta P -- differential pressure -- is the part that makes a dam dive different from a bridge pier inspection. People picture a diver being swept into a pipe by fast water. That is not what gets you. The killer is static head. When your body seals an opening, regardless of how slow the water is, the full head of water acts on the area you've covered. The pressure differential is about 0.433 psi per foot of head. Ten feet of head is about 4.3 psi. That's less than a car tire. But it acts on your chest or your back or your arm. Across that area, it multiplies into thousands of pounds of force. You are not pulling away. You are the plug. The only safe control is positive isolation. That means the gate is closed, locked, and tagged. The penstock is drained, and the drain line is blanked or mechanically disconnected. The turbine is locked out. We don't take the operator's word for it. We walk the system, check each step, and write it into the dive plan. If anything remains open, I do not put a diver in the water. Period. I've seen operators try to keep one unit running while we work in the tailrace. Low flow, they said. The head is still there. The gate slot is still a gate slot. The math still works. That's why our hazard analysis can be longer than the dive plan itself.
The dance with the plant dispatcher
No FERC Part 12 dive happens in a vacuum. The in-water work generally has to happen during an outage or at a steady low flow, which means the plant is losing generation. That makes the schedule a negotiation between the inspection team and the plant's dispatcher. Sometimes we work at night. Sometimes we start at 2 a.m. I once spent three nights at a small hydro plant doing all our inspection between 2 and 6 a.m., because that was the only window the dispatcher could give us. A good dive supervisor plans for that kind of window. All equipment is staged at the top of the gate. Batteries are charged, rigging is inspected, crew is briefed and re-briefed on the lockout/tagout sequence. The dive plan and the plant's water-control plan get cross-checked. The engineer representing the Part 12 team signs off before we go in. At the end, we hand over a record the engineer can rely on: a dive log with locations and depths, video, stills, measurements, and a written description of every significant finding. No exceptions. That's what gets the independent consultant to a confident signature. And that's really the whole job.
Frequently Asked Questions
What is a FERC Part 12 underwater inspection? It's part of the Federal Energy Regulatory Commission's independent consultant inspection for licensed hydro projects. Under 18 CFR 12.30, dams more than 32.8 feet high or meeting the storage threshold are reviewed. The underwater inspection looks at everything below the waterline. Do I need a special certification to dive on a FERC Part 12 inspection? Yes. You need to be a working commercial diver with a recognized qualification, usually an ADCI card. The work falls under OSHA's 29 CFR 1910 Subpart T. A recreational diving certification is not enough. Why is differential pressure so dangerous? When a diver's body seals an opening, the full static head acts on that area. Ten feet of head is about 4.3 psi, but multiplied over the area of a torso, it's thousands of pounds. The only safe control is positive isolation. What does the diver's report include? The consultant needs a measured, documented record: video, stills, dimensions, location references, and enough description to support follow-up. FERC doesn't prescribe the exact dive format, but the independent consultant relies on it.