DEEP DIVING… HOW DEEP CAN WE GO?

Ever wondered what cool sciencey stuff they are teaching undergraduates at the University of Queensland?
 Every school day I will post my newly learned cool fact... Enjoy 

27/02/2013

CHEMISTRY

DEEP DIVING… HOW DEEP CAN WE GO?

What is deep diving? There are many definitions.

Anything below 30m deep is beyond the maximum recommended divers limit.

Below 40 meters, and your beyond the absolute maximum limit specified by the Recreational SCUBA Training Council.

So… How do we make it so our divers can go deeper?

Other than taking a very long time to descend and ascend to get a body used to the intense pressure, there are some amazing tricks with air we can use. 

Ok well, let’s pump some air in a tank and off we go right?

Let’s say you pump in some lovely cheap air.

Nitrogen and Oxygen are the two most common elements in our air; they are the easiest gases to compress into a cylinder for SCUBA.

Bad idea, you just killed your diver.

The problem with air is the types of gas in it. Anything below 10m has the possibility to cause Nitrogen Narcosis. 

Nitrogen Narcosis is an altered state of consciousness where you have the gradual impact that is akin to alcohol consumption or nitrous oxide inhalation.

Anything below 50m and you are potentially experiencing full blown hallucinations.

OK, so when you’re performing a deep dive, the mixture of gasses in the tank is extremely important. 

You want to make sure that you don’t have gas that’s going to cause this narcosis.

The problem is that all gasses (except for Helium and possibly Neon) have these narcotic affects; however they are many and varied in degree. All of them become more pronounced when the breather is under pressure.

When deciding what gasses to put in a deep dive tank, oxygen is an obvious first step; however, like Nitrogen, Oxygen is also a dangerous narcosis inducing gas.

So, we want the smallest amount of Oxygen mixed with something like Helium.

Therefore, to get the deepest possible dives, you must put the minimum amount of oxygen possible in a tank.

The amazing thing is that at deeper pressures you can survive off less and less oxygen. 

This is where the chemistry comes into play.

When you are under a regular amount of pressure the percentage of oxygen in the air is exactly the amount your body will breath in

Eg 21% oxygen in the air at 1 ATM means it’s like breathing in 21% oxygen

However, if you are under pressure the affect is to make it seem like you are increasing the amount of oxygen in the air.

Eg 21% oxygen in the air at 2 ATM means it’s like breathing in 42% oxygen

Using this remarkable chemistry known as ‘Partial Pressure’, SCUBA divers have gotten the oxygen level down to an amazing minimum oxygen air percentage of around 16%!!

So, for the truly deepest of the deep dives, you need to take several canisters of specially made gas, each designed for change over at your decompression stop, so you can go to the deepest depth possible without going crazy on the way down from getting high off the air alone. 

 

This being said… 66m deep is the depth at which compressed air results in what is described as ‘unacceptable risk’ of oxygen toxicity.

The world record for the deepest SCUBA drive is set at 330m

In 2005 the Guinness world records book stopped publishing the record to stop the ridiculously high death rate of those who attempted the record.

These people are crazy…