This article is from the source 'bbc' and was first published or seen on . It last changed over 40 days ago and won't be checked again for changes.
You can find the current article at its original source at http://www.bbc.co.uk/news/world-latin-america-42057864
The article has changed 5 times. There is an RSS feed of changes available.
| Version 1 | Version 2 |
|---|---|
| Argentina sub: What happens when a submarine vanishes | Argentina sub: What happens when a submarine vanishes |
| (about 11 hours later) | |
| A submarine with 44 crew on board remains missing after disappearing off the Argentine coast on Wednesday. | A submarine with 44 crew on board remains missing after disappearing off the Argentine coast on Wednesday. |
| In the last reported contact with the ARA San Juan the sub's captain reported a breakdown relating to a "short circuit" in the sub's batteries. | |
| Why can't subs be detected? | Why can't subs be detected? |
| Submarines are built to be difficult to find. Their role is often to participate in secret surveillance operations. | Submarines are built to be difficult to find. Their role is often to participate in secret surveillance operations. |
| Dr Robert Farley, a lecturer at the University of Kentucky who has written on the subject, says that a sub is very hard to trace if resting on the seabed because under such circumstances it will not be making any "noise". | Dr Robert Farley, a lecturer at the University of Kentucky who has written on the subject, says that a sub is very hard to trace if resting on the seabed because under such circumstances it will not be making any "noise". |
| "Noise, which would otherwise be picked up by what is known as passive sonar, is distorted and [the sub] looks - to active sonar pings - like the sea bottom," he says. | "Noise, which would otherwise be picked up by what is known as passive sonar, is distorted and [the sub] looks - to active sonar pings - like the sea bottom," he says. |
| So how can subs be found? | So how can subs be found? |
| There are a number of ways that the captain or crew can make their location known if in distress. | There are a number of ways that the captain or crew can make their location known if in distress. |
| These methods include sending signal calls to contacts at naval bases or allied ships, or releasing a device that floats to the surface but remains attached to the submarine. | These methods include sending signal calls to contacts at naval bases or allied ships, or releasing a device that floats to the surface but remains attached to the submarine. |
| How long can a crew survive submerged? | How long can a crew survive submerged? |
| The number of days that a crew can survive depends on how long they have already been performing duties underwater and how well prepared they are for losing power. | The number of days that a crew can survive depends on how long they have already been performing duties underwater and how well prepared they are for losing power. |
| "If batteries were charged and air refreshed," Dr Farley says, "then outlook is hopeful". | "If batteries were charged and air refreshed," Dr Farley says, "then outlook is hopeful". |
| In relation to the Argentine sub he adds: "Outer range appears to be ten days if they were well prepared." | In relation to the Argentine sub he adds: "Outer range appears to be ten days if they were well prepared." |
| How is the crew trained for this? | How is the crew trained for this? |
| One of the most important practices is for trapped crew members to slow down their breathing rates in order to conserve oxygen. | One of the most important practices is for trapped crew members to slow down their breathing rates in order to conserve oxygen. |
| Dr Farley says that this it is a hard thing to train people to do, adding that in such circumstances: "My guess is that they would be cautioned to reduce activity and reduce speaking in order to save oxygen." | Dr Farley says that this it is a hard thing to train people to do, adding that in such circumstances: "My guess is that they would be cautioned to reduce activity and reduce speaking in order to save oxygen." |
| The conditions, likely to be cold and damp, may well have a detrimental impact on morale, but the personnel on board will be well trained and disciplined. | The conditions, likely to be cold and damp, may well have a detrimental impact on morale, but the personnel on board will be well trained and disciplined. |
| They will likely establish routines, making themselves as comfortable as possible while minimising their movements and supporting one another as they await rescue. | They will likely establish routines, making themselves as comfortable as possible while minimising their movements and supporting one another as they await rescue. |
| What could have gone wrong? | What could have gone wrong? |
| This remains unclear in the case of the missing ARA San Juan. | This remains unclear in the case of the missing ARA San Juan. |
| But, says Dr Farley, it is possible that an electrical malfunction may have occurred following reports of a fault affecting the sub's batteries. | But, says Dr Farley, it is possible that an electrical malfunction may have occurred following reports of a fault affecting the sub's batteries. |
| Such a breakdown could shut down both the engines and the communication system, he says. | |
| Is there a plan for such accidents? | Is there a plan for such accidents? |
| In the event that a submerged vessel suffers problems in returning to the surface, procedures can be implemented to help raise it. | |
| To control buoyancy, the fuel or ballast tanks - which can add weight - can be emptied and used to lift the sub. To achieve this, the diesel fuel or ballast is released, emptying the tanks, and the chambers are then filled with air. | To control buoyancy, the fuel or ballast tanks - which can add weight - can be emptied and used to lift the sub. To achieve this, the diesel fuel or ballast is released, emptying the tanks, and the chambers are then filled with air. |
| Subs also have small hydroplanes; wings that are adjusted to allow water to travel in different directions as the vessel pitches its bow and stern up or down to assist its movement. | Subs also have small hydroplanes; wings that are adjusted to allow water to travel in different directions as the vessel pitches its bow and stern up or down to assist its movement. |
| What are the main dangers? | What are the main dangers? |
| With a possible shortage of oxygen and a build-up of carbon monoxide, suffocation is the number one risk. | With a possible shortage of oxygen and a build-up of carbon monoxide, suffocation is the number one risk. |
| Oxygen can be supplied either through canisters or generators that perform a process called "electrolysis" - which effectively separates components such as water and oxygen. However a lack of power will hinder this process and the supply may gradually run out. | Oxygen can be supplied either through canisters or generators that perform a process called "electrolysis" - which effectively separates components such as water and oxygen. However a lack of power will hinder this process and the supply may gradually run out. |
| There are other dangers that could also come into play. | There are other dangers that could also come into play. |
| Dr Farley points out that if a compartment within a trapped sub becomes flooded, this can lead to "flash fires and other nastiness" as the air gets further compressed. | Dr Farley points out that if a compartment within a trapped sub becomes flooded, this can lead to "flash fires and other nastiness" as the air gets further compressed. |