Wet Bell Diving: Essential Safety and Operational Procedures
Understanding Wet Bell Diving Operations
Wet bells are used to form a basket with a pavilion where air can be stored. This creates an emergency shelter at the top of the bell in case of equipment failure. Diving support vessels (DPVs) commonly use wet bells in dynamic positioning to transport divers to their workplace.
Advantages of Using Wet Bells
- They provide safe passage through the splash zone and strong tides.
- Umbilicals are kept safe and away from dangers on the ship.
- The amount of air in the rescue can be reduced, providing a safe haven for the diver in the bell, not on the surface.
- The onboard air supply can be used for divers to ascend in a controlled manner, completing decompression if necessary.
- The bell provides a safe and convenient place for decompression in the water.
- While the bell provides a canopy where air can be obtained if the helmet is malfunctioning, it should not be regarded as the primary air supply. The final offer is always the rescue diver.
- The wet bell is also ideal for carrying or storing tools and equipment.
Main Umbilical Components of a Wet Bell
- Primary air supply to each diver.
- Secondary air supplies.
- Communications for each diver and the wet bell.
- Pneumo lines, one to each diver and one to the bell.
- Power for internal and external lights.
- Hot water supplies for each diver.
- Camera cables.
The umbilical is attached to the bell to take the strain off the connections.
Diver’s Umbilical Excursion
The diver’s umbilical is connected to a panel on the bell and stowed inside the bell. It should be marked along its length, either every 10 meters or as company policies dictate. The working diver’s umbilical should be 5 meters shorter than the distance to the nearest opponent. The bellman’s umbilical should be 2 meters long to allow sufficient slack for a rescue.
Importance of Communication in Wet Bell Diving
Good communication between divers and the surface, and if possible, among divers, is crucial. The supervisor must always know where the divers are and what they are doing. The bellman must also inform the supervisor how much umbilical is deployed. Both umbilicals should be marked at intervals of no more than 10 meters so the bellman can see the marks as the umbilical folds. All communications between the divers and the surface should be recorded, and these recordings should be kept for 24 hours or as dictated by the operating company.
Pre-Dive Checks
- Ensure the primary power is on and working.
- Verify that the backup power is working (the easiest way to do this is to switch off the main power and see if communications are still operational).
- Confirm that each diver can hear and be heard.
- Ensure spare disks/tapes are available if needed.
Wet Bell Panel Components
- Main air supply (there might be one for each diver).
- Onboard air supply (high-pressure air reduced through a regulator to about 10 bar).
- Valves to prevent air from passing through the panel.
- Canopy purge (valve to allow air into the bell).
- Diver supplies: These must be designed so that in the event of a cut or severed umbilical, divers are not deprived of the standby diver’s air supply. Onboard air cylinders should be sufficient to get divers back to the surface and complete all decompression.
The diver, therefore, has four supplies available: two on the surface, one on the wet bell, and one on their back.
Checklists for Wet Bell Diving Operations
Ensure all equipment is functioning properly and that all equipment is set up or shut down to allow for a safe workplace. Both the control panel and the inside of the wet bell itself must be checked for correct operation. This will ensure that the valves are working properly and, therefore, comply with legislation and current guidelines.