Uncontrolled descent of diving bell

  • Safety Flash
  • Published on 21 January 2014
  • Generated on 5 July 2025
  • IMCA SF 01/14
  • 2 minute read

A Member has reported an incident which occurred whilst conducting diving operations from a diving support vessel (DSV). 

What happened?

The incident did not lead to any injury or health consequences, but could potentially have been fatal.

As the diving bell was being lowered into the moonpool, two uncontrolled descents were experienced. During the second uncontrolled descent, the bell’s umbilical was damaged leading to a loss of bell pressure. Investigations have shown that the system had been placed in an unsafe condition following operator error and that the programmable logic controller (PLC) had failed to safeguard against these errors. Several layers of additional barriers and backups constrained the actual consequences of the incident to material damage only.

Diving bell

The investigation revealed the following:

  • The implications of introducing PLC technology in to the diving industry may not have been fully understood, and the related roles, responsibilities and competencies of both the technical and operational personnel were not sufficiently clarified.
  • Although the risk management documentation was advanced for a DSV, there was evidence that it lacked continuity and integrity – operator error was not considered.
  • Emergency response to reasonably foreseeable hazardous conditions was not sufficiently defined; for the most effective use, the ergonomic layout, checklists, training and drills requires optimisation. Emergency related processes were not audited for effectiveness or for feedback to improve the related technical, procedural or competency systems.
  • There was insufficient supervisory understanding of both the bell launch and recovery control system. A lack of situational awareness was needed to understand and control the human and equipment response to a complex and hazardous situation.
  • During the development or construction phases, the bell launch control systems were not assigned a SIL rating and consequently, lacked the correct level of safety scrutiny as that given to other, more highly rated, systems.
  • The investigation team identified a number of deviations under various disciplines that the members audit and compliance organisations had failed to detect.

Latest Safety Flashes:

LTI: Hand injury during capstan maintenance

A crew member was injured when their hand was trapped between a wire clamp on the underside of the capstan and the deck.

Read more
High potential incident: Worker injured when opening a flanged assembly

A member of a team of workers dismantling subsea emergency shutdown valves (ESDV) on deck, was badly injured when hit by parts of a valve which were ejected with force.

Read more
Near miss: worker suffers electric shock

A member of a vessel crew suffered a mains electric shock when working on a crane pedestal.

Read more
Unsafe use of electrical equipment in cabins

Crew members were observed inserting 2-pin electrical chargers directly into 3-pin vessel sockets to power their personal equipment.

Read more
UK HSE: load falls from lorry and kills cyclist

A metal heat exchanger, weighing over 2.5 tons, fell from a lorry and killed a passing cyclist.

Read more

IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of the entire offshore industry.

The effectiveness of the IMCA Safety Flash system depends on the industry sharing information and so avoiding repeat incidents. Incidents are classified according to IOGP's Life Saving Rules.

All information is anonymised or sanitised, as appropriate, and warnings for graphic content included where possible.

IMCA makes every effort to ensure both the accuracy and reliability of the information shared, but is not be liable for any guidance and/or recommendation and/or statement herein contained.

The information contained in this document does not fulfil or replace any individual's or Member's legal, regulatory or other duties or obligations in respect of their operations. Individuals and Members remain solely responsible for the safe, lawful and proper conduct of their operations.

Share your safety incidents with IMCA online. Sign-up to receive Safety Flashes straight to your email.