(Breathing) Gases

'Gas' is all around us and fundamental to sustaining life. As divers we need to take our life support systems with us so it's important that we understand the 'gas' that we breath and how much we need!

Initially divers will learn about air and thus use 'air tanks'. As you progress you start to learn about modifying the air into Enriched Air (EANx) and ultimately into Trimix by adjusting the different percentages of the key components (or 'mix') of our original air. From here on we talk about '(Breathing) Gas' because we can be carrying multiple tanks each with different mixes.

"Scuba Air"

So our regular scuba tanks will contain 21% Oxygen and 79% Helium.

For those with dive computers they can set "Air" OR "Nitrox 21%".

Certainly in the USA the recreational diver should be able to trust the contents of these tanks so long as the diver operation can demonstrate that their tanks are certified (anual visual inspection and 5-year hydrostatic tests) AND th eoperation is displaying a current (usually every 3-months) air test for each compressor they have. Note: visual and hydrostatic testing is required on ALL tanks irrespective of their contents.

Scuba air will taste drier than regular air we breath because, as you leanred in your Open Water Course, the air is filtered to remove water which can be destructive to the compressor, storage tanks and diving tanks.

Enriched Air, a.k.a. EANX or Nitrox

We quickly learn that as we get better at diving our air consumption can increase significantly and whereas we used to consume a tank of air in 30 minutes we are now making it last over an hour.

As we go deeper we have plenty of air left BUT still have to surface because our computer or tables tell us to - the issue here is the amount of nitrogen our body is being exposed to. Nitrogen is narcotic and the more we consume (time and depth related) the greater the effect on our body in terms of general ability to focus/keep a clear head and a frequent feeling of being tired after multiple dives.

Dive operators have several ways to modify the air to reduce the amount of nitrogen by increasing the amount of oxygen! The Enriched Air course will teach these methods and explain:

• Why each diver must test the enriched air (to 40% O2) before they dive using an approved testing device and the correct marking on the tanks
• Restrictions on depths they can use mixes to (the more O2 the shallower it can be dived to)
• The decreased equivelant air depth (why the gas is like diving shallower, why you have a clearer head and can feel less tired)
• Why you can dive longer (assuming you have enough gas left)
• Some senible safety precautions

Recreational Trimix

Many people who dive Nitrox want to add a larger margin of safety into their diving so that they have a much greater ability to concentrate by reducing the nitrogen/narcosis even further: they know they cannot use more oxygen because this means their gas can only be used at shallower depths.

To do this they need a third gas. Helium was chosen because:

• It has no significant effects on the bodies ability to breath normally
• It does not require significant changes in diving, i.e. it can be used (within training limits) for recreational No Decompression Limits (NDL)
• It's readilly available
• Specially trained dive professionals can mix the gasses in safety

This new mixture or gas is called TRIMX - a mix of three gases.  Trimix is not just for use in technical diving. It has a very valid place in recreational diving.

The Recreational Trimix course will teach these methods and explain:

• The benefits and sensible limits to Trimix diving
• How to test their gas, mark their tanks and plan their dives accordingly
• The decreased equivelant air depth (why the gas is like diving shallower, why you have a clearer head and can feel less tired) and how to 'pick' mixes for certain dives
• Why you can dive longer (assuming you have enough gas left)
• Some senible safety precautions

Trimix / Technical diving

All recreational diving requires a minimum oxygen mix of 21% - this is called NORMOXIC gas because it can be breathed under normal circumstances (e.g. at the surface) and all the way to the maximum No Decompression Limit of the recreatrional diver, i.e. 130 feet/40 meters.

Beyond 130 feet (subjective) and certainly beyond 200 feet / 60 meters the diver does not want such a high proporation of oxygen because, to be clear, it becomes "poisoness".

We now need to reduce both the nitrogen (narcotic) and oxygen (poisoness) contents. The Helium content must therefore be increased significantly.

At the same time we are now entering the world of mandatory decompression stops to allow our body to safetly return to the surface.

This increases the amount of equipment a diver carries on the dives and even results in the carrying of multiple tanks often containing different gas mixes for different parts of the dive.

The most highly trained, elite, divers are also potentially carrying HYPOXIC gas mixtures. These gases are sufficiently low in oxygen that when breathed at the surface/shallow depths do not contain enough oxygen to support life if breathed for a significant time and can induce the condition known as hypoxia.

Technical dive training gradually introduces more equipmnet, depth and gas mixes

• The benefits and sensible limits to Trimix diving
• Increased equipment, safety and redundancy requirements
• Safety, emergency and rescue skills
• Dive planning & gas selection techniques