JC010: Mud volcanoes and submarine canyons


Deep sea diving: sport under pressure!

The ROV ISIS (pictured right) is used on the RRS James Cook to explore the deep sea. You might think this would make many scuba divers jealous, but there is a very good reason why ISIS has to be used instead of them. Read on to find out why…

As you will probably know when you swim to the bottom of a deep swimming pool it can hurt your ears. This is because the water is forcing your eardrums in with great pressure. In fact at 10m depth, the water has twice the pressure it has at the surface. At 20m depth, there is 3 times the surface pressure, at 30m 4 times and so on. Pressure is measured in a unit known as ‘bar’. Try and work out the pressures involved in the following table:

depth (m)

Diving can be a head-shrinking experience,
as these polystyrene dummies show -
before the dive (left) and after (right).
Image courtesy NOAA.

Scuba diving world record
Scuba diving world record for a blind diver
Underwater extreme ironing World record
Free diving** world record
9min 08sec

*Using standard scuba equipment.
**Free diving is diving with no air source (a bit like in the movie ‘Into the Blue’)

Now you can probably see one reason why divers are not used! Are there any others though?


Another danger divers face underwater comes from the gases they breathe. Apart from running out of air, there are other things which can turn out very serious if you are not careful:

  • The Bends can kill people who come up too quickly from a dive. This is because Nitrogen, which has dissolved in their tissues because of the pressure, comes back out too quickly. This allows Nitrogen bubbles to form in their blood vessels, which s extremely dangerous.
  • Nitrogen can also be dangerous because of something known as ‘Nitrogen narcosis’. Nitrogen narcosis happens when breathing normal air underwater. At depths of about 30m, the Nitrogen in the air that the diver breathes changes slightly, and the diver can start to feel drowsy, giddy, or even to act drunk because of it! This becomes worse the deeper the diver goes and at up to 90m, hallucinations can be quickly followed by unconscious.
  • Believe it or not, at around 50m depth, even oxygen can be a problem as it will turn toxic!

Due to the above risks, there are other gas mixes (‘Nitrox’, a special mix of Nitrogen and Oxygen and ‘Trimix’, similar to Nitrox, but also contains Helium) which divers can breathe. These increase the time limits and depths of their dives and can also reduce the chances of getting the bends.

The bends are a serious problem to consider
when doing your ironing under water.
(image source: underwatertimes.com)


Temperature also decreases as you go down in the water. This is because the infrared waves, which carry the thermal energy, cannot penetrate the water to depth, so it stays very cold. In fact, sea water at around 400m and below is roughly the same temperature as a normal household ‘fridge. This makes a diver breathe more quickly (think you getting in a cold shower!) and can also make them hypothermic.

Even though ISIS was expensive to make, is expensive to maintain and operate, it is still much safer, gets better results and is probably ultimately cheaper than having divers do the (impossible) job that it does. 

Can you find who achieved the diving world records, when and where? Also, do you know what SCUBA actually stands for?

Any questions? Ask us using the question and answer page

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