Working under pressure

The job of a Royal Navy diver is hazardous and physically very demanding. QinetiQ experts played a central role in making this challenging job as safe as possible.

Early diving experimenters quickly discovered it is not enough simply to supply air in order to breathe comfortably underwater. The pressure of your inhaled breath must exactly counter the surrounding or ambient pressure in order to continue to inflate your lungs. By always providing the breathing gas at ambient pressure, modern demand valve regulators ensure the diver can inhale and exhale naturally and virtually effortlessly, regardless of depth. For some diving applications and deeper dives beyond 30 metres gas mixtures other than normal atmospheric air (which is 21% oxygen, 78% nitrogen and 1% other) are used. With the right mix of gases and the right equipment a trained diver can today descend to depths that would have been thought impossible decades before.

A position of trust
No-one better understands the potential effect of deep dives on the human body than Sea Division’s Maritime Life Support business group. The team was formed in 1987 when the Experimental Diving Unit at HMS Vernon in Portsmouth was moved to share premises with the Royal Navy Physiology Laboratory (the roof was blown off their Portsmouth facilities in the storm of October 1987). Today the team, based near Gosport, use their years of experience in support of divers from the Royal Navy, Army, Royal Engineers and Special Forces.

The team not only draws on decades of data and experience, they have access to three man rated dive chambers and an unmanned hyperbaric test chamber which allow them to conduct trials on dive equipment, both with and without human subjects, under safe, controlled conditions. Tim Sharman, Business Group Manager, explains: “We have a unique resource here but more importantly the MOD trust us to deliver sound and practical recommendations. Without the right equipment divers, already operating under extreme conditions, can succumb to potentially life-threatening conditions like decompression sickness and nitrogen narcosis. In theatre it becomes even more important that divers are operating at the peak of their abilities.”

Pushing back the boundaries
In 2005 the team were approached by the Underwater Warfare Systems IPT and the Royal Navy Superintendent of Diving to help extend the capability of the RN Clearance Diving Branch. This team of divers are trained in bomb and mine disposal and underwater engineering and respond to bomb disposal tasks all over the world. QinetiQ were asked to help the Royal Navy identify equipment and procedures that would restore their ability to dive to depths of 60 m.

The equipment currently in use, the Clearance Diving Breathing Apparatus, came into service in 1997 and was designed to allow dives to a depth of 81 m. In practice though it has several operational issues and cannot be used at this depth. At 40 kilos it is too large and too heavy to allow the diver to manoeuvre effectively. It exhibits excessive hydrostatic imbalance and is therefore hard to breath while swimming for extended periods. It also has an inappropriate bail-out system for diving to 81 m and as such is unable to provide sufficient emergency gas for a diver to reach the surface safely should his main breathing system fail. . All of these factors mean it in fact has a maximum operational depth of 42 metres. Gavin Anthony, QinetiQ Fellow and Principal Consultant Diving and Life Support, explains: “We have a very structured approach to this kind of test and evaluation exercise. The first task was to establish the specification for the equipment in order to achieve the capability the Royal Navy was looking for. Candidate equipment was then put through a series of unmanned and manned tests in our dive tanks and chambers.”

The candidate equipment that was selected is an enhanced variant of the range of re-breathers already used operationally by the MOD and the German Navy. Baseline data was already available from tests on previous versions of the equipment and this, coupled with the equipment’s pedigree, made the Clearance Divers Life Support Equipment (CDLSE) the natural choice for the trials. The aim was to establish how ergonomic the equipment is; its ability to enable the diver to switch from a closed-circuit to open-circuit bail-out breathing system; whether it would safely support the user through a wide range of exertion at different depths as well as the endurance of the system.
The first set of tests was unmanned and designed to identify any major issues with candidate equipment. They also helped to establish the safety parameters for the manned tests that were to follow. Before the programme could proceed to manned tests of any type, the proposed approach needed approval from the MOD Research Ethics Committee. The tests are in fact classed as human experimentation and the Committee is responsible for the review and approval of all non-clinical research using human subjects undertaken, funded or sponsored by the MOD. Once the Committee were satisfied that the correct ethical protocols would be followed approval was given for the manned phase of the testing.

Safety first
The manned trials were conducted with a team of QinetiQ and Royal Navy divers. The ergonomic trials were conducted in Ocean Basin at Haslar where the water was shallow (5 metres) but there was a lot of space to move around in. “We videoed the diver operating equipment, moving and swimming, completing mine warfare tasks and safety and rescue procedures,” states Gavin. “The diver gave us feedback on a questionnaire on his experience and we then analysed this and the video footage to assess the ergonomic performance of the equipment.”

The next stage was a series of chamber dives at the Deep Trials Unit (DTU). In the chamber the diver is in only two and a half metres of fresh water at four degrees centigrade, but the pressure in the chamber is increased incrementally to mimic increasing depth of water to the maximum test depth of 60 m. Sensors record the diver’s breathing pattern as he is in the ‘wet pot’ section of the chamber, meanwhile in the dry section of the chamber another Royal Navy diver stands by in case the diver needs extracting from the chamber. A QinetiQ team member is also in the dry chamber doing the experimental work required inside the DTU. Other QinetiQ team members monitor proceedings from outside the dive chamber.

The test involved the diver being taken to 30 m on an oxygen and nitrogen mix; 40 m also on oxygen and nitrogen and then to 60 m on an oxygen and helium mix. At each stage the diver used an underwater bike (ergometer) to put the body under stress as it would be in operational situation. Gavin explains: “As the diver pedals we can increase the work they have to do incrementally to establish whether the equipment continues to support them. The bike can be swung through variety of positions to mimic swimming and stationary work positions.”

The tests established that it was not acceptable to take divers to 40 metres on an oxygen and nitrogen mix and that this mix of gases should be used only up to 30 metres. However, it was shown that the equipment could successfully support a diver at depths to 60 m and allow him to return safely to the surface, using oxygen in helium gas mixtures.

The final set of tests focused on the acoustic signature of the equipment. “Marine mines can be fused to explode through sound,” explains Gavin. “Therefore it’s critical that the diver’s equipment operates within certain acoustic boundaries.” The equipment was dived in the Experimental Diving Tank (EDT) filled with murky sea water from Portsmouth Harbour. The EDT is lined with sound proof panels (known as anechoic panels) to block out external ambient noise. Sensors measured how much noise the equipment makes compared against NATO’s acoustic guidelines.

Making the grade
After compiling all their results the team found that the equipment was simple to use and would support a diver undertaking hard work at depths to 60 m. Their conclusions were presented to the MOD project safety committee and on the basis of the trial results the committee decided to proceed to Royal Navy user trials. The QinetiQ team was tasked with producing the protocol for the trials prior to review by the ethics committee. The Royal Navy have now taken the equipment into open sea for trials over a period of a few months and the QinetiQ team are providing ongoing support on a consultancy basis. Providing the open sea trials are a success the first production sets are due for delivery and deployment later in 2008.

“Royal Navy divers have to operate in dangerous and difficult circumstances and it’s rewarding to be able to make a real difference to their working conditions,” summarises Tim. “When the CDLSE comes into service it will be a significant step towards restoring the Royal Navy’s 60 m dive capability, but importantly in a way that is safe and viable in real life operational scenarios.”