During diving activities on two occasions in the same 24-hour period, a diver noticed that there was no pressure left in his bail-out bottle. The decision was taken by the Dive Supervisor to recover the diver from the water, as per standard protocol. After recovery, the bail-out bottle and appliances were checked, and it was found that the high pressure content gauge hose on the bail-out was damaged.
Both hoses were replaced for new hoses.
What went wrong?
The short interval in which these two incidents happened triggered an investigation which revealed the following:
- There were two different types of damage:
- cuts; most likely caused by sharp mussels and stones (illustration above left)
- damage caused by bending and overstressing (illustration above right);
- Both hoses were leak tested and found to be leaking through holes near the ferrule connector;
- Both hoses were fitted with bend restrictors;
- The hoses were maintained and tested in accordance with Code of practice for the initial and periodic examination, testing and certification of diving plant and equipment
- The hoses were subjected to a regular visual inspection before every dive;
- Both hoses were in use for up to 4 years and were regularly used.
What were the causes?
Investigation suggested that one type of HP hose is prone to damage near the ferule connector, caused by bending and stressing, regardless of the use of a bend restrictor present at this location. The damage was not sustained in one single occasion but is believed to have developed over time.
What actions were taken?
There are different types of HP hoses on the market with specific characteristics:
- Hose type 1: fatigue like damage may occur near the ferrule over time. When this damage occurs, it can lead to loss of the bail-out within a dive. In order to reduce the risk of this type of damage occurring, annual replacement may be required, depending on usage.
- Hose type 2: does not show the same fatigue damage development as the construction is more flexible and rugged.
|Hose type 1||Hose type 2|
|Appearance||Thin, smooth, black, shiny||Thick, black, dull-coloured|
|Dimensions||Outside diameter 10.8mm||Outside diameter 12.5mm|
Thin layer, plastic-like type (shrink fit)
Soft woven middle layer
Rigid inner layer, hard plastic-like tube
Thick outer layer, rubber compound
Soft woven middle layer
Flexible thick inner layer, rubber compound
|Other findings||Layers can move freely from each other
Outer layer easily cut with knife
Stiff, hard to bend, inner layer tends to buckle
|Layers are vulcanized to each other
In general, hard to cut with a knife
Easier to bend, smaller bending radius, inner layer does not tend to buckle
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