Failure of dive chamber overhead door centre pin

What happened

Minutes after a dive team transferred from the entry lock into the diving bell, there was a failure of the diving bell overhead door centre pin. A “bang” was heard and it was seen that components of the top door mechanism had failed.

The bell and dive system remained safe, there was no loss of pressure. Following discussion with the team onboard the door was lowered in a controlled manner supported by the diver recovery hoist in conjunction with the top door hydraulic ram. The divers were transferred to an adjacent chamber and the system made safe.

The top door hinge pin, weighing 0.5kg, fell from its position approximately 1.8m to the deck of the entry lock; there was no-one in the entry lock at the time.

What went wrong?

Our member notes that investigation is still ongoing including (and not limited to) design review, metallurgical analysis etc.

This failure appears to be limited to this specific design of hinge and operating mechanism. It should be noted that the hydraulic ram did not act directly onto the pin that failed. The hydraulic ram was, however, directly attached to the door (via clevis).

Our member estimates that the door would have been operated between 1500 – 2000 times per year for an average diving year (200-250 days diving), and suggests that the root cause is likely to be design related, corrosion and cyclic stress fatigue cracking (applied over many years).

What actions should be taken?

Doors with a similar design should be checked for cracks at the earliest opportunity.

Members may wish to review:

Safety Event

Published: 22 July 2021
Download: IMCA SF 20/21

Relevant life-saving rules:

Line of Fire

IMCA Safety Flashes

Submit a Report

IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of all. The effectiveness of the IMCA Safety Flash system depends on Members sharing information and so avoiding repeat incidents. Please consider adding [email protected] to your internal distribution list for safety alerts or manually submitting information on incidents you consider may be relevant. All information is anonymised or sanitised, as appropriate.

IMCA’s store terms and conditions (https://www.imca-int.com/legal-notices/terms/) apply to all downloads from IMCA’s website, including this document.

IMCA makes every effort to ensure the accuracy and reliability of the data contained in the documents it publishes, but IMCA shall 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.