Saving sailors in sunken submarines
Submarines, manned or unmanned have been vital in learning about the deep sea as well as playing an essential role as part of our armed forces. But sometimes, subs get into trouble. Unlike the passengers of a surface vehicle, submariners don't have the option to simply bailout into lifeboats which make submarine accidents very dangerous.
To help save lives in these thankfully rare situations, Britain, along with France and Norway have funded the development of the NATO Submarine Rescue System or NSRS which is a project delivered by Rolls Royce.
Jonty Powis is a retired submarine commander who now works for Rolls Royce as a submarine expert.
Jonty - Well if you ask people how many submarines have been lost at sea in peacetime, most people can name the Kursk and one or two others, but the truth is, since the end of World War II, at least 34 submarines have sink. So submarining generally is a dangerous activity.
Ben - What sort of things are likely to go wrong?
Jonty - Collision is perhaps the single most important reason that submarines sink. Many of those 34 submarines were lost in collision.
Ben - What actually happens? What do the people inside experience?
Jonty - We've done a few trials actually. We've parked a submarine on the bottom which you can do and it's quite interesting because they go on to a minimum diet, very little water, high complex carbohydrates. The sort of biscuits they eat are ghastly.
But the principal issue is going to be one of boredom and that boredom is complicated by the fact that if they're in elevated pressure. Eventually you're going to get an onset, if the pressure goes up sufficiently, of nitrogen narcosis. It is essentially a drunken sensation.
But of course, having a sunken submarine which is a pretty dangerous environment, full of people who are inebriated or suffering from nitrogen narcosis is an even more dangerous situation.
Another issue which isn't generally appreciated is that with the normal constituent of the atmosphere, as you raise the pressure, oxygen starts to become poisonous. There's a thing called 'oxygen toxicity' which essentially starts when the partial pressure of oxygen exceeds about half an atmosphere. So that's above about 25 to 30 meters of immersion. So you've got really quite a knotty medical problem to deal with once you extract these guys.
Ben - So, what is it that we're now hoping to do, or what is it that the NATO Submarine Rescue System has been trying to do?
Jonty - Well, submarine rescue really kicked off just before the Second World War. There was an American system based essentially on a diving bell which you could winch down to a submarine on a wire. It would attach itself to a prepared mating surface around the escape patch, pump out the water in-between and then hydrostatic pressure held it on, and you could get guys, 8 or 9 at a time, back to the surface.
So the idea of rescue grew wings, more or less literally, in that the Americans invented a thing called the DSRV, the Deep Submergence Rescue Vehicle which is capable of being flown anywhere in the world and rescue the guys 24 at a time.
At the same time, the Brits early in the '80s, realised that it was probably a good idea to develop some sort of capability of our own. So we modified a North Sea oil rig maintenance and diver transport submarine called LR3, subsequently replaced by one called LR5, and they could be used to mate to a distressed submarine on the bottom and extract people.
NSRS which went into service in 2007 is a much better system, completely air transportable, capable of reaching anywhere in the world in somewhere between 72 and 96 hours. That might sound a long time, but you would expect people to survive for perhaps as long as 7 days. So that gives us a margin to actually find them, reach them and rescue them.
Ben - So what happens for us back here on land? When we first hear that there is a submarine in trouble, what are the processes to then kick off?
Jonty - You're going to be confronted with a submarine relatively close to shore, one imagines. Too deep though for them to make a free ascent to the surface. So the alert will go up, a buoy will be released or something will arrive in the surface, the Inmar Sat satellites will very quickly produce a position which is quite accurate to within a couple of hundred yards. We then have two systems we deploy. One called intervention which is relatively small. This consists of a remotely operated vehicle, relatively lightweight set of equipment, and they can actually deploy to the scene about a day before the rescue system. They localize the submarine very precisely, survey it, establish communications with the people surviving inside, if possible. They can also engage in what we called 'pod posting' where watertight pods of life support stores of food, medicine, clothing, whatever you like can be posted into the submarine through one of the escape towers. So, when the rescue system turns up, some 24 hours or so later, we would expect the submarine to be ready for rescue.
But how do we get there? Well the system is stored, broken down into its constituent elements, no component except the submarine weighs more than 16 tonnes, so they can be readily transported by flatbed lorry, delivered to an aircraft, and flown to the sea. We can get the whole system on a prepared deck, secured, in about 18 hours. You then know that there's no point staying alongside, time to sail. The hyperbaric treatment centre is then commissioned on the way out there, and that means you would arrive on scene and you would just launch the submarine immediately and once you've got 30 or so guys out, that's one leg of the hyperbaric treatment centre filled, shut all the hatches, start the decompression process. Meanwhile, the submarine is still working like a little underwater ambulance.
Ben - What does the rescue sub actually look like?
Jonty - It's white. It's rather stubby and about 10 metres long and about 3 ½ meters high, and underneath the submarine hangs an inverted cup which is the skirt, the mating skirt which has a simple rubber seal around its bottom lip, and that's what makes the seal. Remember it is only hydrostatic pressure which holds this on, a considerable force, about 1.8 tonnes for every metre of immersion. It has a large window at the front. It might sound a very trite thing to say, but that window is one of the secrets of our success, the ability for the pilot inside the vehicle to actually see what he's doing. In exercises, we've demonstrated the ability to leave the surface, go to the disabled submarine perhaps 80 to 100 meters below the surface and achieve a mate in less than 15 minutes. Remotely operated vehicles can also do it, but it takes considerably longer.
Ben - I assume that it's versatile and if - heaven forbid - you did have to use it, it would actually work with most if not, all of the submarines that are currently out there.
Jonty - Yes, that's an interesting question. For some time, NATO had been running an annual working group which looked at submarine rescue and escape. It's an opportunity to see what other people are doing. Gradually, the NATO standards have been accepted across the world. Virtually, anything you can think of has now got a NATO standard applied to it. Touch wood - if we find ourselves going to a rescue - the ability to have everybody following the standard has meant the saving of life has been made incomparably more likely.