Diving and Underwater Ship Husbandry: What Could Go Wrong?

As Diving Manager at the International Marine Contractors Association (IMCA), and as a former commercial diver, I have spent many years observing the same pattern around the world: underwater ship husbandry (UWSH) remains one of the most hazardous segments of the commercial diving industry. Despite advances in technology, training and regulation, the number of serious accidents and fatalities in this type of work continues to be unacceptably high. 

In this article I summarise some of the key messages I have presented recently at various events, including the UWSH seminar held in Panama during the annual meeting of the ADCI Latin America & Caribbean Chapter. I will focus on three main areas where things tend to go wrong: decompression incidents, differential pressure (Delta P) incidents and failures in lock out / tag out (LOTO) systems. All of these are reflected in IMCA D082, Guidance on Diving Operations in Support of Underwater Ship Husbandry, a free download intended to help the industry reduce the accident rate in this sector. 

In 2024, IMCA launched a dedicated UWSH campaign built around three main pillars: the publication and promotion of IMCA D082 – Guidance on Diving Operations in Support of Underwater Ship Husbandry, the organisation of technical seminars – such as the Singapore UWSH Seminar, which brought together 215 attendees from 15 countries – and participation in expert groups such as IOGP’s UWSH Expert Group. The aim is straightforward: to provide practical guidance to operators, shipowners, and contractors who engage or manage underwater maintenance on ship hulls. 

It is important to note that UWSH is not core business for most IMCA diving contractor members working offshore, but IMCA cannot ignore the reality: the number of diver fatalities in this type of work remains extremely high. In 2023 there were at least nine known UWSH fatalities, and in 2024 at least four more, in countries such as South Korea, Singapore, and Sweden. These are only the ones that have been reported; there are likely to be others. 

Within this context, IMCA D082 provides a structured framework around three elements which are almost always present when things go wrong: people, paperwork (permits to work, risk assessments, procedures, LOTO), and equipment. When a serious accident occurs, we almost always find deficiencies in at least one of these three pillars – and often in all of them. 

One common type of incident is decompression illness. We looked at three real cases which occurred in Scotland, Spain, and Brazil. In each of them, the diver was working at relatively modest depths, between 6 metres (18 feet) and 26 metres (86 feet), and a deck decompression chamber (DDC) was located nearby: on a jack-up rig in Scotland and on the quayside in Spain and Brazil. 

However, in none of the three diving teams was there anyone with the confidence and competence to operate the chamber safely. In two of the cases, the diver had to be transported to a third-party hyperbaric facility that was not ready to accept casualties. The result was delayed treatment and, in two out of the three cases, permanent injury to the diver. 

The lessons are clear. It is not enough simply to have a chamber. We must address what we call skill fade – the loss of practical ability through lack of use. The only way to mitigate it is through regular drills and familiarisation: full chamber checks, review of the location and use of medical equipment, gas management, operation of main, medical and entry locks, knowledge of treatment tables, and practice in the use of BIBs. If the team does not train, they will not be ready when a real incident occurs. 

In addition, when third-party hyperbaric facilities are used, the diving contractor must carry out verification checks in advance: is the facility fit for purpose, resourced for 24-hour operations, supported by an agreed and tested communications protocol, logistically accessible, and truly ready to accept an injured diver? Placing reliance on a facility that has not been properly assessed can turn a treatable incident into a permanent disability. 

Another recurring category of incidents in UWSH is associated with differential pressure, or Delta P. This refers to situations where there are significant pressure differences across openings, valves, sea chests, intakes, or temporary structures such as cofferdams and plugs. In these conditions, a diver can be sucked into an opening or trapped by the failure of a wooden plug or inflatable bung. 

We see three common patterns: fatalities involving divers being sucked into un-isolated openings; fatalities caused by the failure of plugs or bungs which were poorly selected or installed; and fatalities linked to mechanical Delta P where systems were believed to be isolated but were not, usually due to weaknesses in the lock out / tag out process. 

The conclusion is that Delta P is not an abstract concept – it is a very real hazard which must be addressed in the risk assessment of any intervention near sea inlets, valves, propulsion systems, or hull structures where water flow may occur. If the team does not understand where Delta P can arise and how it can be eliminated or controlled, the diver is operating within a false sense of security. 

The third group of incidents concerns the isolation of vessel systems – in other words, lock out / tag out. In UWSH this will typically involve propulsion systems, thrusters, pumps, and any part of the vessel’s plant which can create zones of suction, flow or hazardous mechanical movement for the diver. 

A robust LOTO process should follow at least six basic steps: a risk assessment carried out by competent personnel from both the vessel and the diving contractor to identify all hazardous plant and equipment; shutdown of the relevant plant and equipment; physical isolation of those systems; fitting of lock out / tag out devices to each energy-isolating device so that they cannot be reactivated; a stored energy check, ensuring that any residual energy in components is relieved or restrained; and, finally, verification of isolation before diving begins. 

When these steps are not followed, or are completed only on paper, we see what I describe as the architecture of an incident. One typical example: during manoeuvring operations, a large vessel fouls a fishing net in a stern thruster. The port authority has pre-audited and approved diving contractors and protocols are in place. However, a SCUBA diver is deployed with a broom and a knife as his tooling, with no lifeline, no fully dressed standby diver, no structured communication with the supervisor and a bridge team who believe, incorrectly, that isolations have been applied simply because there has been a previous ROV inspection. What is treated as “only a quick job” becomes a high-risk operation with very little defence against a serious accident. 

If we look across UWSH incidents, we almost always see deficiencies in three areas. The first is people: questionable qualifications, undersized diving teams, supervisors without specific experience, no dressed standby diver ready to enter the water, and a lack of emergency diver recovery arrangements. IMCA has even seen membership applications containing forged UK HSE diving certificates, IMCA diver medic (DMT) certificates and CSWIP 3.1U inspection certificates. If we start from invalid credentials, the entire safety system is weakened. 

The second area is paperwork. Permits to work, LOTO procedures, risk assessments, communication protocols, and emergency plans must not only exist; they must be understood, applied and reviewed with appropriate frequency. Any management system is only as good as the people implementing it in the field. 

The third area is equipment. In many of the most recent UWSH fatalities, divers were working in SCUBA configuration without surface-supplied gas. Out of the last 20 known UWSH diving fatalities, only one involved a diver using surface-supplied equipment. That statistic speaks for itself. A professional surface-supplied diving system with a control panel, communications, and a fully dressed standby diver dramatically reduces the likelihood that a single point failure will lead to a fatality. 

IMCA’s UWSH campaign and the D082 guidance document are built on a simple premise: no death or serious injury is acceptable. One poorly managed isolation, a lack of understanding of the risks that the vessel itself brings to the diver, or a shortcut justified as “only a quick job” can leave a family without a loved one. The ripple effect of each accident will last a lifetime. 

Changing this reality cannot fall solely on diving contractors. It requires a genuine commitment from shipowners, operators, port authorities and any organisation that engages underwater ship maintenance. We need to review how UWSH operations are managed today, establish clear policies and procedures, provide training and support to our teams, strengthen permit-to-work and LOTO systems, and ensure that planning and supervision keep diver safety at the centre. 

IMCA D082 provides a process map and a structure to plan, manage and execute these operations with multiple layers of defence. But no single document will change an industry on its own. That change will only come if we are willing to apply its recommendations in practice. Only then can we realistically aspire to a situation where every diver who goes under a ship’s hull to work returns home safe and healthy at the end of the day.