Differential pressure. The hazard that defines dam diving.
Nearly every diving fatality at dams, intakes and water plants has the same cause. It isn't depth. It's water moving from one side of an opening to the other. This page explains what it is, why you can't see it, and what we do before anyone enters the water.
Water at two pressures, separated by a hole
A closed gate has water at one level above and another below. An intake has the reservoir on one side and a pipe on the other. If there is any opening between them, however small, water moves through it with force. That force is differential pressure, ΔP. A few meters of head across an opening the size of a hand produces more force than a diver can overcome. It pins the diver against the opening or pulls him into it. There is no letting go.
Because you can't see it or feel it until it's too late
The water makes no sound. No bubbles, no swirl on the surface. The diver works on a gate everyone believes is closed, moves near a leak nobody knew existed, and is trapped. The supervisor on the surface only sees that the umbilical stopped moving. That's why differential pressure isn't managed with care. It's managed with procedure.
Before the first dive, not during it
Identify every opening.
Gates, valves, pipes, trash racks, outlets, bottom drains. Anything that connects two bodies of water. We do it with the owner's drawings and the people who run the plant.
Close, lock and tag.
Every gate or valve that can create flow is closed, physically locked and tagged. Nobody operates it while a diver is in the water. The plant operator signs the lockout with us.
Verify there is no flow.
Closed is not the same as sealed. Before the diver approaches, we measure. A Swoffer current meter at the opening, and when needed an ROV that inspects the gate or intake before a person does. If we can't confirm pressure is equalized and there is no leak, the diver doesn't approach.
Plan the dive around the hazard.
The diver knows where every opening is, works on a surface tended umbilical, and never puts his body in front of an opening that hasn't been verified.
There are jobs we turn down
If a gate can't be locked, if the owner can't confirm a drain is closed, or if pressure can't be equalized, we don't enter the water. We find another way to do the work, or we wait for conditions to change. A contractor who agrees to dive in those conditions isn't doing you a favor. He's handing you the risk.
What we need from your plant before we arrive
- Drawings of the structure showing every opening and conduit
- An operator with authority to close and lock gates and valves
- Water levels above and below the structure
- Access to verify the lockout in person before the dive
This isn't paperwork. It's the difference between a finished job and a phone call nobody wants to make.
Have a gate, intake or trash rack that needs work?
Let's go through the openings, the lockout and the plan before we talk about dates.
Technical reply in under 24 business hours.