Extended endurance saturation diving emergency bailout system - Doug Austin Global Business Development Manager Divex
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Extended endurance saturation
diving emergency bailout system.
Doug Austin
Global Business Development Manager
Divex
Purpose of Presentation To describe the development of a new extended duration saturation diving secondary life support system, which provides fully autonomous gas supply to a saturation diver in the event of a loss of his surface gas supply. The system is designed to provide a low-cost and simple to operated emergency breathing system which allows all divers to have adequate time to return to safety – regardless of working depth The new system is named COBRA
Background The commercial diving industry has made many advances in diver safety over the last 30 years, however one of the most significant risks facing the diver remains the loss of his primary life-support through his excursion umbilical. IMCA members have reported incidents in the recent past where divers have been compromised by a loss of surface breathing gas or a severed umbilical. Divex have for 20 years manufactured the SLS emergency rebreather, however the unit has only been adopted in very deep water areas, such as Brazil, or in countries such as Norway where legislation requires it’s use.
Conventional open circuit bailout systems In the majority of saturation diving operations the diver is deployed wearing only a SCUBA type single or twin cylinder of compressed breathing gas, which the diver can access if his surface gas is compromised. As this gas can be breathed only in open-circuit mode, the diver will consume this gas very rapidly. SCUBA sets were not designed for this function, and indeed 1st stage regulators and helmet emergency valves are not designed for the increased flowrates incurred in saturation dives.
Legislation / Guidelines The current duration requirements for divers bailout is described and proscribed in NORSOK U-10024, ADC International Consensus Standards for Commercial Diving and Underwater Operations, and IMCA D024 in their requirements as follows: Bail-out system (NORSOK) The bail-out system shall be ergonomically adapted to the primary system, and it shall be possible to activate with no more than two operations. When a diving bell is used, the bail-out system shall be designed to ensure easy entrance.
Bail-out system (NORSOK)
The bail-out system should in general have sufficient capacity to allow the
diver to reach a place of safety. As a minimum, the bail-out system shall
provide the diver with the gas for 10 min based on an average
consumption of 62.5 I/min, correlated to the ambient pressure.
Under these requirements, an open-circuit bailout described previously
(twin 7 litre 300 bar) is restricted to the following depth:
2 x 7 x 280 bar (assumes 20 bar residual) = 3920 litres available gas
Diver requires 10 mins at 62.5I = 626 litres at the surface
Maximum depth therefore is 3920/626 = 6.27 bar ata or 53 metres
or 175 ft
IMCA D024 Rev 1 Section 10 2.2 states:
The cylinder(s) must have sufficient endurance to allow the diver to return to the bell in an
emergency. This will normally mean that a calculation should be available showing that the
capacity of the cylinder(s) at the depth of diving will allow breathing gas for 1 minute for every 10
metres of horizontal excursion. This calculation should be carried out using 40l/min as a minimum
consumption.
At these figures, and assuming a 50 metre excursion, the open-circuit
bailout set will meet the requirement to the following depth:
- Available gas 3920 litres
- 40I/min X 5min = 200
- 3920 / 200 = 19.6 bar ata or 186 msw/ 615 ft
ADC Consensus Standard Section 6.3.6 Diver worn emergency gas supply , or bailout, shall have a minimum calculated four-minute supply at the calculated depth. Section 11. Calculates that 2 x 7 litre cylinders would provide 4 minutes of bailout gas at 200msw ( 660 ft).
Open Circuit Bailout Duration Assuming the IMCA breathing rate of 40 litres/min, the following chart represents the limitations of typical twin 300bar, 7 litre open-circuit bailouts.
Is 5 minutes enough? This presentation, if I am running to schedule , has already lasted more than 5 minutes – is it that really enough time to allow a potentially compromised diver to return safely to the bell? What if this could be extended to 45 minutes?
COmpact Bailout Rebreathing Apparatus ( COBRA) With the aim of designing a new rebreather to support diver emergency breathing at all depths, Divex have developed the new COBRA system.
COBRA Description COBRA is a fully back-mounted semi-closed mixed gas rebreather, designed to provide greatly extended autonomous breathing gas to a saturation diver in the event of loss of his surface gas supply. The system works by injecting fresh heliox gas into a semi- closed breathing loop to maintain a breathable diving mixture. Carbon dioxide exhaled by the diver is removed in a Co2 scrubber, and the diver breathes in and out to a counterlung assembly.
COBRA Description Increasingly there is a recognition in the diving industry that the same extended bailout breathing facilities typically employed in deep dives, should be available not only to divers operating at extreme depths (greater than 200m / 660 fsw) but also in the depths more common in the world’s oilfields – typically 50-200 msw / 165-660 fsw). With the increased use of extended excursion umbilicals from increasingly bigger diving bells, the time required to return to the safety of the bell can be extended, and the combination of cold water, darkness, subsea structures and the divers understandable alarm and disorientation can all contribute to delays in a successful return.
COBRA ENDURANCE
The figure below shows the relative endurance, at 120 metres depth, of a
conventional, open –circuit 300bar 7 litre twin bailout, the existing SLS Mk4 set,
and the new COBRA set. The endurance is calculated using a conservative
breathing rate of 40 litres per min.
7 litre 300 bar Twinset SLS Mk4 COBRA
7 minutes 25 seconds 30 minutes 45 minutes
It is clear that the conventional bailout approach would severely limit the diver’s
ability to return to the bell, especially in cases such as a DP failure and subsequent
vessel run-off where the bell may have been dragged some distance. An incident
such as this occurred in the North Sea in 2012.COBRA Duration
OPEN
CIRCUIT
DURATION
DEPTH CHARGING PRESSURE DURATION (40L / MIN)
50 msw 300 bar (max) 45 mins * 16.5 mins
100 msw 300 bar (max) 45 mins * 9 mins
150 msw 300 bar (max) 35 mins 6 mins
200 msw 300 bar (max) 27 mins 4.5 mins
250 msw 300 bar (max) 24 mins 3.75 mins
300 msw 300 bar (max) 21 mins 3 mins
350 msw 300 bar (max) 19 mins 2.7 mins
400 msw 300 bar (max) 16 mins 2.4 mins
* Duration limited by CO2 Scrubber Canister DurationRebreather Technology Semi-closed and fully closed circuit rebreathers are not new technology. Rebreathers are however used predominantly in military applications, where typically divers are deployed untethered to depths up to 100msw. These miltary divers are deployed to undertake clandestine swimming operations or mine clearance operations, the latter frequently deployed at greater depths using heliox gas mixes. Divex has many years experience in designing and manufacturing these mixed-gas rebreathers, and a great deal of the technology developed in producing these sets has been employed in producing the new COBRA set for the commercial saturation market.
COBRA system
Diver / Operator Acceptability The COBRA set has many operational advantages over the current SLS MK IV. Divex has incorporated diver feedback into the new design resulting in the following features and advantages: Pre-Dive Test- While the existing SLS set is a “parachute” as regards operation, the new COBRA set can be mechanically switched on and off by the diver as a pre-dive check. The divers surface supply is completely isolated when the COBRA set is activated, but remains available should the surface supply be restored. On actuation, the diver breathes through a bite mouthpiece which further isolates the diver from the risk of a flooded helmet.
COBRA Features cont. Fully Back Mounted The COBRA counterlung is completely encapsulated on the divers back. The SLS Mk4 has chest mounted counterlungs which some operators reported were restrictive and interfered with chest “D” rings and harnesses. The work of breathing of the COBRA counterlung is a significant improvement against the SLS Mk4.
COBRA Features cont. Co2 Scrubber The COBRA CO2 scrubber is a granular-filled axial scrubber which provides optimum CO2 absorption across a wide range of diving depths. The scrubber performance has been tested to show that at depths Of 350 msw, breakthrough of CO2 occurs only after 45 minutes, when the diver has been breathing at 62.5 l/min for the first 10 minutes of a bailout “incident” and at 40 l/min thereafter. These breathing rates are used as it is likely a diver will be agitated and breathe heavily in the event of a lost umbilical or surface gas, but will be unable to sustain this breathing rate for long, and will reduce his breathing rate once the bailout set is activated and the diver is less agitated.
CO2 (ppm)
COBRA with SODALIME Granule Filled S/S Box (Filled to 180mm)
0.5% SEV
350MSW 2%He 40 and 62.5RMV 1.6 and 2.5 l/min Injection Rates
26/07/2013 Absorbent: SODALIME Granules
Diver Orientation: Horizontal 1.0% SEV
450 Test Medium: Freshwater 4
Water Temperature: 3.87- CO2 Injection Rate
5.74DegC
(lt/min)
400 CO2 Injection Rate: 1.6 & 2.5
lt/min 3.5
Breathing Rate: 40 & 62.5 RMV
Tidal Volume: 2.5 Litres
350
Depth:350 msw 3
Gas Supply: 2% He
Scrubber Packed By: B Morris
CO2 Injection Rate (lt/min)
300
2.5
CO2 (ppm)
250
2
200
1.5
150
1
100
50 0.5
0 0
0 5 10 15 20 25 30 35 40 45 50 55
Duration (Minutes)Elevated PPO2 The partial pressure of oxygen ( PPO2) in the COBRA breathing loop will vary according to the diver’s workrate, however even at extreme breathing rates the PPO2 will not fall below 0.3bar Typically, the divers PPO2 will be elevated to around 1.35bar at 40l/min breathing rate. This elevated PPO2 will allow the set to be safely breathed for some time after the cylinders have become exhausted.
COBRA Features cont. High Flow Positive Pressure To prevent water ingress into the set, either in use or prior to activation, the set is kept positively pressurised. As the diver descends, the system demand valves flow gas into the set to maintain this positive pressure. The depth sensing demand regulator which maintains the positive pressure in the scrubber canister has been designed with increased flow to allow the diver to make rapid downward excursions without having to wait for the set to “keep up”. Size Smaller than existing SLS MK4 backpack, and a standard open-circuit twinset with buoyancy. Weight and Transportability Lightweight with easily detachable diving weights, to enable easy handling through locks and in workshop.
COBRA Features cont. Cylinder Charging Easily removable carbon-wrapped twin cylinders accessible for charging and maintenance. Improved Actuation Single turn activation and de-activation and no counterlung “ripcord”. A criticism of the SLS set was the potential “sticking” of the counterlung release cords, particularly when diving in fine silt. Positive Pressure Indication Safely indicator Heads Up Display mounted on divers helmet for easy reference. This indicator displays a green signal to the diver at all times to show the COBRA scrubber canister is maintaining a positive pressure and therefore dry and ready for use. If the indicator is red, the positive pressure has been lost and the diver should abort the dive. A cylinder pressure indicator shows graphic cylinder pressure.
Positive Pressure Indication
COBRA Features cont. Scrubber Hotwater Jacket to Ensure High CO2 Performance on Actuation A splitter block is attached to the divers hot water manifold, and is attached to a small bore hose which feeds hot water around the scrubber canister. This fits a standard hot water suit manifold. The scrubber is significantly more efficient when warm, and so the system is continually ready for optimum performance. Once activated, the system maintains heat by the exothermic reaction of Co2 absorption in the scrubber canister.
COBRA SUMMARY The COBRA set has been designed to be as simple as possible to operate and maintain. The set is completely mechanical, and relies on no complex electronics for its operation. Like all Divex breathing systems, the equipment is robust and reliable and has a very low work of breathing. COBRA is designed with the intent that the diver should not require to have to think about his life- support equipment, but to be allowed to focus on the task in hand, knowing the life support is always there when required. COBRA is currently undergoing unmanned testing in Divex breathing simulator to depths of 500m, and undergoing CE testing and certification to EN 14143
COBRA ANIMATION
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