
	Home • About us • Expeditions • Technical • Starfish Enterprise • Links

100m Bail Out Scenario

Annual Emergency Skills Training - Supported by Divers' Lodge in Hurghada, Egypt

Above: Nick Gilbert & Adina Ochert during the final phase of the ascent

Most would accept that there are inherent risks associated with trimix diving but when primary life support fails and divers resort to secondary backup systems these risks increase significantly.

If something adverse does happen we generally respond with a series of Predetermined actions; as per training. However for deep trimix dives where carrying enough OC gas to complete the decompression schedule is impractical, bailing out becomes a team effort requiring rapid response from a well trained surface support team.

In such an emergency, one option is to lower decompression gases, in suitably sized cylinders, to prearranged depths on a drop line. The ascending diver then recovers each cylinder in turn and switches to the new gas - an essential survival skill for deep trimix divers. However, as the gas switch from a high to low helium mix takes place the diver is exposed to a further risk of DCS brought on by Isobaric Counter Diffusion.

If serious injury - or even death - is to be avoided during an emergency ascent meticulous planning backed up by reliable equipment is paramount, but having the equipment in place is only part of the solution; divers and support teams must also be familiar and confident in its use.

Training Expedition

Many of our recent deep-wreck expeditions have opened up a wealth of new and challenging opportunities, but as many of these locations are a long way from recompression facilities the risk of permanent injury or death increases significantly should a problem occur. In these environments having tried and tested emergency procedures could mean the difference between walking away from a problem and life in a wheelchair.

With this in mind we decided to organise a one-week training expedition to sharpen our emergency bail-out procedures. The culmination of the exercise being the ultimate test of any rebreather bail-out strategy: the simulation of a catastrophic and unrecoverable failure of the breathing loop at 100 metres.

Although deliberately putting ourselves in a bail-out situation may seem somewhat counterintuitive, it would give us the opportunity to rehearse in a controlled environment with the option of reverting back to primary life support equipment if ‘lounge based’ ideas weren’t quite going according to plan.

Left: Our dive boat MY 'Shorouk Sat' at Abu Ramada Right: Hurghada in January from our hotel room

Location

Finding a location to safely conduct the exercise with a surface support team we could trust on was our first consideration. Premier technical dive centre Diver's Lodge in Hurghada was the obvious choice, as they have supported us on a number of occasions whilst carrying out build up training for earlier deep-wreck diving expeditions.

We discussed our ideas with the company’s Chairman Karim Helal, and operations manager Wessam El Sebai who, as usual, were only too pleased to help. As an added bonus technical diving instructor Leon Kusters - who had just joined the Divers’-Lodge team - saw our deep bail-out ideas as an opportunity to test and practice their emergency response procedures.

We have known Karim for some years and have always been impressed with his commitment to safety, however this time he surpassed even our expectations by providing us with our own boat and crew to ensure everything would run as smoothly as possible; we are very grateful to him for this

Planning

The plan was for one diver to switch from their CCR to OC bail-out at 100m. The second diver would assume overall control and monitor the exercise throughout, with the agreement that the bailing out diver would without question revert back to their CCR if directed to do so by the controlling diver.

After reviewing options, the island of Abu Ramada was chosen for the exercise. It is a sheltered location with a steep drop-off, enabling us to perform the drill with the dive boat close by.

As the ‘carried’ bail-out gas would only suffice for around 25% of the total decompression schedule a surface deployed drop station was decided upon to provide staged decompression gasses for the remainder of the dive. Taking our initial design Leon built the drop station and worked out the best strategy for its deployment.

A number of hours were spent reviewing both OC and CCR decompression schedules. The aim being to optimise gas mixtures to ensure both CCR and OC bail-out schedules were as close a match as possible; especially during the initial ‘deep’ phase of the bail-out where it is important to keep both divers together.

After cross-checking various plans using a variety of decompression tools we decided to use the VR3 as it offered the best safety margin and gave us the opportunity to test its OC gas switching function – a subject that has received an amount of bad press in the past for being over complicated. As an additional safety measure tables were also carried.

During the course of the ascent the bailing out diver would be required to switch from rich helium-based trimix to a weaker trimix and eventually nitrox. At the early gas switch points the diver may be exposed to considerable risk of a bend caused by Isobaric Counter Diffusion, basically jumps in nitrogen partial pressure. Mark Ellyatt was kind enough to provide us with a copy of his new DecoCheck program (the latest Windows application being a massive improvement on the original Excel version) which we used to fine tune our gas mixes and switch depths; the software was versatile enough for us to modify the initially generated schedule to include VR3 based deep stops.

Left: The classroom at Divers' Lodge used for planning and preparation Right: Leon building the drop station

Final Preparation

The evening before the dive the three of us carried out a final walk-thru of the plan. Predicted OC gas usage was confirmed and cylinder fill pressures checked. ‘Actions on’ in the event of a real problem were reviewed as well as abort checkpoints.

The next day, on arrival at Abu Ramada, we were relieved to see our boat steam past the curfuffle of day boats, snorkelers and obligatory overexcited Italians to a sheltered and secluded part of the reef with the deep clear blue of the drop-off directly under our stern. Ideal!

Leon wanted to test the deployment of the drop station and make some last minute adjustments so before we began our preparation he kitted up and entered the water. The visibility was excellent that day and from the surface we could clearly see him tying in some more ‘D’ rings at 21 metres.

(A little while later, with the drop station recovered and stowed back on the boat, we had a final chat about the planned procedures, actions on etc and kitted up for the dive.)

Above: Final walk-thru of the plan just prior to the dive

The Drill

The initial part of the descent was made at a fairly relaxed pace giving us a little time to tune in to our environment as we descended close to the reef wall. At 60 metres we adjusted our profile and adopted a relaxed frog kick following the steep terraces away from the blue and into the twilight below. The descent time to our target depth was a little over 8 minutes, giving plenty of time to be orientated and comfortable.

After a pre-arranged signal Nick (who picks up the story) checked the colour coding on his bail out regulators to ensure he would be breathing the correct gas, closed and removed the rebreather mouthpiece and switched to open circuit. The VR3 was also switched from CCR to OC mode.

Suddenly the silent and relaxed world of the rebreather was shattered by the noise of bubbles and metallic hiss of low pressure gas filling the regulators second stage.

The speed at which you can chew through gas at extreme depths is quite alarming and I could actually see the pressure gauge on my 12 litre side mount move a little each time I took a breath. This was more stressful than I had anticipated and the almost overwhelming desire to ascend to a less gas-expensive depth took some effort to get under control. I forced myself to remain in control of the ascent.

Three minutes into the drill I reached the first deep stop at 70 metres. After exchanging signals with Adina that all was OK I had a little time to consider the situation. My gauge was reading 150 bar. A quick mental calculation indicated my equivalent Surface Air Consumption to be around 30 litres per minute; 50% higher than I’d expected but still just within our safety limit. Up until this point I realised that I had been doing little more than reacting to my new situation and not really thinking ahead. This first deep stop was an opportunity to focus, relax and get my breathing rate under control before moving off.

Left: Adina Ochert Centre: Monitoring the ascent Right: Nick Gilbert (Open CCT)

At 54 metres we exchanged signals confirming the next deep stop and I concentrated on my next task which was deploying the yellow emergency SMB. I also took the opportunity to switch on my remaining OC bail-out gasses on the VR3. This took a few button presses but was straightforward and made easy by ensuring all bail-out gasses were saved and grouped together for easy access. The VR3 recalculated the decompression schedule presenting a time to surface of around 90 minutes – as expected.

After completing these tasks the two of us reassessed the situation. I was now down to my last 70 bar but my breathing rate was definitely beginning to settle. Another quick calculation confirmed that I could make the one remaining deep stop and still get to the intermediate gas switch depth at 40 metres; but with very little gas remaining from an initial 220 bar fill.

As I continued to empty the aluminium 12 litre stage cylinder it became very light, producing a slightly annoying pull to the left, and even though I was correctly weighted without stages I had to maintain minimum volume in all air spaces to counter its effect.

On clearing the third deep stop I prepared to switch to my intermediate decompression gas of trimix 20/30, and after confirming the colour code on the regulator I signaled my intention to Adina. A full 12 litre cylinder of gas to breathe from was certainly a welcome relief, and with the deep phase behind me I felt myself relax a little more; the VR3 quietly reminded me that this wasn’t the time to ‘chill’ and prompted me to confirm the gas switch.

Above: Ascent using the line from the drop station

At 24 metres there was still no sign of the drop station, and I started to fuss about ascending much further on my 20/30 trimix when I knew the drop station would arrive with a cylinder of Nitrox 50 at 21 metres. Would I descend and get it, could I pull it up or would Leon appear and sort the problem out?

It was just over 12 minutes since I had deployed the yellow SMB and it started to dawn on me that this had perhaps cut things a little fine for surface support. However, as we arrived at 21 metres Adina drew my attention to the welcome sight of Leon swimming the drop station over to attach it to the SMB line.

Even though this was a drill and I was quite capable of aborting the bail out at any time and returning to my rebreather, I must admit to a sense of relief at seeing not only the drop station but the support diver as well; the latter certainly offering a great psychological boost.

On reaching the ascent line of the drop station I tied off my reel and removed my extremely light and almost empty stage cylinder of bottom gas (trimix 11/60), clipping it onto a spare ‘D’ ring. I then unclipped the Nitrox 50 from the line and attached it to the ‘D’ rings on my harness; checking the labeling to ensure there hadn’t been a mix up with the oxygen cylinder at 6 metres. After signaling my intention to switch gasses to Leon and Adina I made the switch and confirmed my new gas on the VR3. I also deposited my intermediate trimix onto the shot line as - at that point - I didn’t believe it was required.

The rest of the ascent was relaxed and uneventful and at 6 metres I swapped my nitrox 50 for the staged oxygen. However, once on the oxygen my CNS began to climb very quickly. In fact before the end of the dive I was being prompted by my VR3 to perform an air break. This is where my intermediate trimix might have come in handy and in future I would carry this with me to the 6 metre stop. As Adina was with me, though, I just pinched some of hers. Leon had actually considered this and had returned to the surface to get a cylinder of air just in case. Good skills Leon. So despite best efforts, retrospectively this is certainly something that ought to have been taken into account during early planning. Normally we do, but this time our support diver was most valuable.

Left: Picking up fresh gas and clipping off the empties Right: Emergency SMB deployment

Discussion

In all this was a very constructive exercise with many lessons learnt for us and the team at Divers’-Lodge.

A combination of regulator performance at depth, gas density, slight exercise and stress almost doubled the expected gas consumption at the beginning of the bail out. This fits with our observations during actual bail-out situations where, during the early stages, we have seen gas consumption exceed 60 litres per minute - hypercapnia will certainly cause this and should be factored in as a realistic expectation when planning CCR bail out gas requirements.

At the end of the dive the bottom gas was down to around 20 bar but the trimix 20/30 intermediate gas still had 100 bar remaining. Also, the gas switch depth of 40 metres was borderline for potential Isobaric Counter Diffusion problems. It would therefore make sense to switch to the intermediate gas a little deeper and consider running a slightly richer trimix.

It’s important to give the surface support team as much warning as possible. Sending the SMB up from 54 metres gave Leon only 12 minutes to deploy the drop station, which he managed, but only just. The SMB needs to be deployed as soon as possible after the incident to give the support team time to respond and resolve unforeseen issues, possibly obvious… Always carry enough reel line reach the surface from the target depth.

Using oxygen at 6 metres pushed Nick to his CNS limit very quickly and resulted in a requirement for air breaks. Using nitrox 80 from 9 metres (Leon did suggest this but for some reason we ignored him) dramatically reduces CNS with only a negligible increase in the decompression schedule. We may well consider use nitrox 80 for future expeditions.

Bailing out successfully from depth (where you survive and don’t get bent) is not a straightforward operation and requires a lot of planning and coordination. As soon as the switch to OC has been made bailing out CCR divers are in a completely different ball-game. Rapidly dwindling gas supplies, emergency SMB deployment, maintaining a steady ascent rate, changes in buoyancy and switching computer(s) from CCR to OC mode all add to the task loading. Overcomplicated ‘couch based’ strategies are a sure route to the incident pit; survival depends on planning ahead and above all team work and keeping it simple.

The Team

From left to right: Leon Kusters, Adina Ochert and Nick Gilbert

Sponsors of the 2003 HMS Vandal Expedition