A member has reported an incident in which two divers were injured following the failure of a diving bell door. The incident occurred following some bell internal maintenance and surface bell checks, when the bell was being pressurised back onto the saturation chamber system at a depth of 130 feet to allow the two divers to transfer under pressure back to the saturation chamber.
During final checks, dive control were informed by the Life Support Technician (LST) that the seal between the transfer under pressure (TUP) module and the trunk was not possible as he suspected that the door was not ‘dogged’ tight enough shut. The divers were informed, in the bell, of the situation with the top door of the TUP and that the internal bell door would have to come back up so that the dogs on the TUP could be properly secured. Minutes later, the divers were told by the dive supervisor the bell door was about to be opened again. As the bellman was opening the bell door and was about to secure it with the safety chain, the second diver stepped on the rim of the opening before the safety chain was secured. At this instant the door fell onto his feet. The dive superintendent was informed instantly that there had been a failure and the diver’s feet were trapped.
The bellman tried to lift the door off the injured diver’s feet using the diver recovery lifting equipment (mazdam), but due to the weight of the door he was unable to lift it. In attempting to lift the door with the mazdam, the bellman wrapped the rope around his right hand to give extra leverage. At this point, the second diver grabbed the same rope section below the divers hand and pulled sharply downwards, trapping the bellman’s hand in the rope, causing injury to the hand.
It took around thirty minutes to finally release the diver’s feet before he could be transferred into the system for treatment. An initial evaluation of both divers was undertaken and it was clear that one of the divers had suffered significant trauma to both feet whilst the other suffered a serious injury to his right hand. The emergency response team were contacted ashore and medical advice was sought. The divers were decompressed over the next two days and subsequently transferred to a hospital ashore for examination and subsequent treatment. Diver one had suffered fractures and soft tissue damage to both feet and diver two had suffered severe bruising with swelling and tissue damage to his right hand.
Our member’s investigation noted the following:
- The hydraulic ram used to open and close the door had failed;
- When the ram cylinder was opened, it was identified that the shaft had broken internally at the end where the locking nut holds the piston onto the shaft causing the shaft to pull freely from the cylinder body. This resulted in the door dropping down in an uncontrolled manner;
- The hand operated hydraulic Enerpac pump had a greater operating pressure than that of the ram and relied on a pressure relief valve to prevent over-pressurisation;
- Additionally, the failure of the door component prevented free movement of the door during the bellman’s attempt to raise it so as to release the trapped diver’s feet.
Our member noted the following causes:
Foot Injuries (lost time injury (LTI))
- Direct Cause:
- Failure of the hydraulic ram piston rod threaded end at the locking nut inside the ram, resulting in the ram piston rod detaching from the unit, thus allowing the door to fall;
- Underlying Root Causes:
- Failure to secure the door in an open position
- Incorrect placement of divers feet
- No Planned or Preventive Maintenance System in place for the hydraulic ram
- Safety Risk Assessment for hydraulic use not applied or assessed
- No secured guard around trapment area to prevent incorrect foot placement
- Single point failure, no stage latchment of door during raising operation, preventing door closing
- Too much hydraulic pressure facilitated by hand pump to ensure opening of door;
- A factor in these root causes was that there was a design failure of the door securing ram system, having a single point failure with no backup.
- Direct causes:
- Divers hand placed in a rope bite; . Indirect causal factors:
- Human error and reaction to emergency situation
- Lack of induction training regarding correct equipment usage and potential hazard.
This was a very nasty incident, and similar incidents have occurred in the industry in the past. Ensuring that secondary systems are in place to prevent unplanned closure of the door, and ensuring that door hydraulic systems are included in planned maintenance schedules, will go a long way to preventing recurrence.
Members may wish to refer to the following similar incidents (key words: ram, bell, door):
- Near-miss: Internal bell door (fell shut narrowly missing bellman’s feet)
- Failure of chamber door hydraulic actuator
- Bell bottom door hydraulic operating system failure
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