Working With a Diving Bell: A Practical Guide
A diving bell is a rigid chamber lowered into the water to transport divers to and from the seabed while maintaining surface pressure inside. The Byford Dolphin Bell operates on the same principle as any other open-bottom diving bell used in commercial saturation diving, though its specific configuration and incident history are worth noting separately. What follows is the operational procedure, not a history lesson. The core components you need to understand before operating or working near a bell are the bell structure itself, the umbrella deck, the ballast tanks, the life support panel, the communications system, the diver lock-out mechanism, and the lifting frame attached to the vessel's crane or A-frame. Everything else is auxiliary. Here is how the cycle actually runs in practice:
Pre-submersion checks. Verify that all ballast tank valves are closed and sealed. Confirm the life support panel is reading correct O2 at 21% and CO2 scrubbers are fresh — lithium hydroxide beds turn from white to pink when exhausted. Check the umbilical bundle for twists, cuts, or chafing points. Test the bell-to-deck communication circuit and the internal intercom. Pressure-test the hatch seals at 1.5 times working pressure if the bell has been out of the water for more than 48 hours. This usually takes about 45 minutes if nothing is wrong. Diver loading. Divers enter through the top hatch while the bell is still on the deck. They are tethered, helmet-checked, and given a final gear inspection. The hatch is closed and pressure-equalized before lift-off. Never skip the visual check through the sight glass — I've seen a diver's face mask not properly secured because the loading sequence was rushed, and that's an immediate abort condition. Descent. Ballast tanks are flooded in a controlled sequence. The bell sinks at roughly 10 to 20 meters per minute depending on the vessel's heave compensation and sea state. The crew on deck monitors depth, vessel position, and umbilical pay-out. Once the bell reaches the work depth, water floods the open bottom until internal and external pressures equalize. At that point, the divers can exit through the bottom hatch into the water, breathing gas from their own cylinders while the bell atmosphere remains at surface pressure.
Work period. The bell acts as a dry refuge. Divers return between tasks to breathe 100% oxygen at surface pressure, which accelerates nitrogen washout. Surface-supplied gas is routed through the umbilical. Temperature inside the bell typically runs cold — seawater cooling the metal walls is the main factor, and I always make sure spare drysuits are stowed inside for the wait periods. Decompression. This is where most people misunderstand the process. The divers do not decompress inside the bell at elevated pressure in the traditional sense. Instead, they return to the bell at work depth, the bell is lifted to the surface, and then the internal pressure is gradually reduced over a set schedule. The decompression tables for the bell are calculated based on the depth-time profile of the dive, not the time spent inside the bell. This is a common point of confusion. If the work depth is 60 meters for 90 minutes, the bell decompression schedule might take 3 to 4 hours depending on the gas mix and the diving contractor's approved tables. Lift-off and recovery. Ballast is blown, the bell rises, and it is secured on deck. Hatch seals are depressurized and verified. Divers exit and are handed over to the hyperbaric chamber team for any continued treatment.
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A Real Problem: Umbilical Snag on Ascent
I once had a bell recovery where the umbilical drum jammed partway through the ascent. The bell was at about 30 meters and starting to rise when we lost pay-out. The immediate risk was the umbilical being tensioned against the bell skirt and potentially damaging the gas or voice lines. We stopped the ascent, lowered the bell back to 30 meters, and manually freed the line by having a diver on the seabed inspect and clear the snag. It added roughly 90 minutes to the cycle. The workaround that has saved me on two other jobs since then is running a separate tension-monitor line — a thin stainless steel messenger cable that goes through the same fairlead but isn't under load. If the messenger shows tension while the umbilical drum is idle, you know something is catching before it becomes a crisis. The Byford Dolphin Bell incident in 1985 is taught in every commercial diving course, but not for the reason most people think. The catastrophic event was not a standard bell malfunction — it was a deck blowout during a decompression stop. The living bell was pressurized to 13 bar when the upper deck was accidentally separated, causing near-instantaneous explosive decompression. The technical takeaway is about pressure boundary integrity and the importance of positive isolation procedures when working on pressurized habitats. Modern bells have redundant pressure monitoring and interlocked access systems that prevent exactly this kind of scenario. Still, understanding what went wrong matters more than memorizing the timeline. Another counter-intuitive point: bell time is not dive time. Divers can spend hours in the bell at depth without it counting toward their decompression obligation, because the bell atmosphere stays at surface pressure. This is the entire reason bells exist in saturation diving — they separate the work environment from the decompression environment. But it also means divers can become complacent about their individual cylinder reserves. I've seen divers assume the bell atmosphere means they have unlimited air when they actually only have their backup cylinder, which is typically rated for 30 to 45 minutes. Always check your personal supply before exiting the bell.
Limitations and When Not to Use a Bell
Diving bells are expensive to mobilize. A standard open-bottom bell with a two-diver capacity and full life support will set you back anywhere from $15,000 to $40,000 per week depending on size and specifications, not including the support vessel. They also require a vessel with a certified lifting capacity of at least 3 to 5 tons for the bell alone, plus dynamic positioning or a good anchor system. If your work depth is under 30 meters and the job only requires a few short dives, a bell is overkill — surface-supplied diving with a standby diver is faster and cheaper. Bells also struggle in high-current environments. Even 1.5 knots of lateral current can make landing and securing the bell difficult, and anything above 2.5 knots is typically a no-go unless you have a guided bell landing system. The ballast control system can compensate for vertical movement, but lateral drift is a real constraint. If you need a bell-specific manual or schematics, the original Byford Dolphin Bell was built by Crichton-Vulcan and later maintained by various contractors. General operational manuals for similar bells — such as the International Marine Contractors Association (IMCA) guidance documents IMCA D 044 and IMCA D 017 — cover the safety procedures and maintenance intervals for bells in this class. Those are publicly available through the IMCA website and are the closest thing to an authoritative reference for this type of equipment.
