It is a common misconception that the use of a platform for recovering SPHL is a good idea.
I write this blog to further saturation diver and SPHL crew safety and provide some detail on the reason why a platform should not currently be used for recovery of a SPHL.
Some diving companies and O&G operators have believed that as part of their Hyperbaric Evacuation Plan (HEP), it is ALARP / a good idea to sail the SPHL to a nearby platform; pick the SPHL up using the platform crane and then lower it onto a standby vessel for rapid transit to their HRF. This sounds good in concept, although it is not.
Below are some critical risks that need to be addressed:
The risk of shock loading when landing on a vessel;
The method of hook-up to the platform.
The introduction of new hydrocarbon related risks; and
The man riding capabilities of the platform cranes.
Some of the above risks are manageable (particular the later two); however, the first risk, that of shock loading the occupants is not easily managed nor engineered. The risk involves the vessel heaving/going up when the SPHL is being lowered down by the crane. When the highly rigid SPHL connects with the vessel, it causes an impact and very fast deceleration of the occupants.
In lay mans’ terms - the issue is that a 20t mass with people rigidly connected to it is being forced to stop almost instantly.
This impact can be reduced by placing a large number of rubber tyres on the deck with which to land on. However, even with such an attempt to absorb shock, the shock level remains high and calculations show that simple rubber tyres are not sufficient to suitably absorb the shock.
If one was to make a suitable shock absorbing system, it should be:
Engineered/calculated to ensure allowable deceleration;
Ensure no risk to the bottom SPHL pressure flange;
Tested/independently verified (ie. By a Classification Society (e.g. DNV GL / ABS)); and
A recovery drill conducted.
Without doing the above, using a platform in the HEP introduces risk to the divers which is high and it cannot be considered an ALARP approach to hyperbaric evacuation.
Pleasingly, this shock risk is well managed in other personnel transfer operations; for instance the FROG personnel transfer device by Reflex Marine. This system has large shock absorbers under each seat to reduce the shock load. The FROG system has been independently impact tested. Reflex state that prior to this system, up to 11% of casualties were as a result of this shock load.
All lifeboats are tested in accordance with the Life Saving Appliances code which requires impact and drop testing. During this impact testing, the accelerations are assessed and in order for the lifeboat to pass, it needs to be below acceptable values of deceleration. The reason for such testing is to reduce the risk of personnel injury during the deployment of a lifeboat. Clearly the effect of colliding with water is far lower than it would be when impacting a vessels deck moving upwards!
An SPHL is a very rigid structure – allowing negligible shock absorption.Any such shock would be passed directly into the chamber and the dive team.
Really such an approach should not be a point of discussion, but one of show me the calculations, independent certificate and drills/testing!
“Our core focus is ensuring the safe recovery of saturation divers in the event of a diving catastrophe”