Underwater Ship Husbandry - key steps the sector must take to protect diver safety

Underwater ship husbandry has the highest fatality rate of any sector of commercial diving. Bill Chilton, Diving Manager at the IMCA and member of the IOGP’s Ships Husbandry Expert Group, sets out the key steps that the sector must take to reverse this trend and support diver safety.

Underwater ship husbandry (UWSH) entails all aspects of the upkeep of the hull – including valves, sea chests, intakes, and discharges – and associated appendages – such as propulsion systems – of a ship or other floating structure.

Vessel owners and operators frequently have a need for UWSH. These projects normally comprise inspection, maintenance, repair, or cleaning – either to remove biofouling from the hull to prevent the growth of invasive non-native species, or to increase hydrodynamics and therefore reduce costs by minimising transit times fuel use.

Tragically, UWSH can also be extremely dangerous work.

We know from numerous diving fatality investigations that, where a fatality occurs, one or more of three things have failed: people, procedures, or equipment.

In terms of the people involved in the diving project, there maybe simply not enough of them. In 2024 IMCA published its internationally-recognised Guidance on Diving Operations in Support of Underwater Ship Husbandry (Guidance Document D082). This states there must be at least five people in a dive team for it to operate safely: a diving supervisor, a working diver, a standby rescue diver, a tender for the working diver, and a tender for the standby diver. Additional people may be required to operate or maintain specialised plant, such as winches or brush carts, and to assist in an emergency

Even if the team has the required numbers, the personnel involved maybe untrained, incompetent, or not aware of the suite of risks that a vessel can pose to an underwater diver.

UWSH diving projects should be led by procedures covering risk assessments and emergency plans. However, it is the failure of the ‘permit to work’ system – which should prevent the vessel’s crew from receiving permission to undertake any work that may impact diver safety – and ‘lock out / tag out’ procedures – that prevent mechanisms such as engines, pumps, or waste discharge from operating – that pose a particular risk, and have led to numerous diver fatalities. The operation of a vessel’s propulsion system, and other machinery that creates a hazard for divers, such as differential pressure, needs to be identified and mitigated with suitable physical controls in place.

Most crucially, the majority of diving fatalities on UWSH projects have involved divers working without proper equipment: all too often, divers are sent to work wearing recreational scuba gear. In contrast to commercial ‘surface-supplied’ diving equipment, a scuba suit has no umbilical connecting its wearer to the surface, providing the diver with air to breathe and a means of communicating with, or being located by, their on-board crew.

The biggest impact the marine construction sector can have on the high fatality rate in UWSH projects would be to ensure that all UWSH work is undertaken using surface-supplied diving equipment rather than scuba.

In summary, UWSH has the highest fatality rate of any sector of commercial diving. The majority of these deaths occur when divers use recreational scuba gear. To progress a way forward and to reduce diver fatalities, the first step must be to ensure that any diving contractor on an UWSH project uses surface-supplied diving equipment.

Once established that recreational scuba gear is unacceptable, then efforts should be made in the other two areas; the number and competence of personnel in a diving team, and the management systems used to control risk and exposure to hazards.

IMCA Guidance on Diving Operations in Support of Underwater Ship Husbandry (Guidance Document D082) is available to IMCA members and non-members, and can be downloaded here: https://www.imca-int.com/resources/technical-library/?sourceID=83a0951d-f17e-ee11-8179-6045bdd0ecdb

Bill Chilton has 28 years of experience in the commercial diving industry. Before joining IMCA, he worked at the UK Health & Safety Executive for 12 years as a Diving Specialist Inspector, regulating the safety of divers working in the offshore energy and other sectors of the diving industry. Prior to this, Bill worked as an air and saturation diver as well as in a variety of topside positions, including project engineer and project manager.