Trimix 101: What is Trimix and What is it for?

With the popularity of Technical Diving in recent years, one of the first things that comes to mind is "Trimix". So what is this trimix, can it be eaten or drunk? What benefits do we get..?

Trimix: Helium, Nitrogen and Oxygen

Trimix, meaning triple gas mixture, is the name of the gas mixture and diving type that is generally used for deep dives, consisting of a mixture of Oxygen, Helium and Nitrogen gases in certain proportions. We know that the need for Trimix diving arose due to some obstacles experienced in deep dives with air. In this case, let's list the general problems that deep diving with air (21% O2, 78% N2, 1% other gases);

• Oxygen Toxicity

• Nitrogen Narcosis

• Decompression İllness

  
  

1. Oxygen Toxicity

As taught in open water - advanced scuba diving courses, oxygen with increasing partial pressure can have harmful effects on the human body over time. We have examined the details of oxygen poisoning in a separate section, but the general acceptance is that when diving with air, we are at risk of oxygen poisoning when we go deeper than 60 meters (200 ft), that is, when the partial pressure of oxygen exceeds 1.4 atm.

So if we want to go deeper than 60 meters (200 ft), we must first reduce the oxygen ratio of the gas we breathe. Of course, it is also necessary to know that we cannot reduce the oxygen as much as we want, for a breathable mixture, the partial pressure of oxygen should not be below 0,16 atm. For example, a mixture containing 8 percent oxygen should not be breathed at depths shallower than 10 meters (0,08*2 bar= 0,16 bar).

2. Nitrogen Narcosis

Another problem that stands out in deep dives with air is nitrogen narcosis. Again, as we learned in our first diving lessons, the increase in the partial pressure of nitrogen can cause certain effects on the human body. To summarise very briefly; high partial pressure nitrogen gas can slow down the transmission between nerve cells and cause a decrease in the speed of thought and reasoning ability. In this case, it creates an effect similar to drunkenness underwater. Although this effect is not permanent, it can lead to dangerous situations or make it difficult to do anything underwater such as taking photos, tightening a nut, tying a rope/rope. We even have difficulty remembering a wreck we dived on or a living creature we saw. The effects of nitrogen narcosis start to be felt around 40-50 meters (130 - 165 ft) on average in dives with air, depending on the water conditions and the psychology of the diver.

The conclusion from this is that if we are going to dive deeper than 40-50 meters (130 - 165 ft) and do something underwater or carry out an examination, we need to reduce the nitrogen ratio in the gas we breathe in order to avoid the effects of nitrogen narcosis.

The way to Trimix; Reduce Oxygen and Nitrogen!

According to the results of oxygen toxicity and nitrogen narcosis, if we want to dive deeper, we need to reduce the oxygen and nitrogen ratio in the gas we breathe. So how do we do this? We need to add another gas or gases to reduce nitrogen and oxygen. While doing this, the gas or gases we add, should not react with nitrogen or oxygen in any way. For example; if you reduce oxygen and nitrogen and add hydrogen instead, hydrogen can react with oxygen and cause an explosion. In order to use a mixture of hydrogen and oxygen, the oxygen ratio should not exceed 4 percent.

At this point, helium, a member of the noble gas family that does not undergo any chemical reactions, comes to our rescue. Helium does not react with oxygen or nitrogen, which makes our job a little easier. If we fill the tube that we will breathe with a certain amount of helium and complete the rest with oxygen and nitrogen (or directly air), we will have prepared a mixture that contains less oxygen and nitrogen than in the air. The more helium we add, the more we can reduce the oxygen and nitrogen ratio.

Of course, let's get to the problems of helium. First of all, helium is not a cheap gas that can be found very easily. Helium, which was produced in laboratory environments for many years, later became partially affordable when it was found in helium gas beds similar to natural gas beds. Still, for an average trimix dive, it is necessary to spend 300-400 bucks for helium according to today's value. In other words, we cannot add helium as much as we want :) If that were the case, we would not mix nitrogen at all and would dive directly with a helium-oxygen mixture, which we call Heliox. However, primarily in order to avoid costs, we keep nitrogen in our mixture and Trimix, which is a 3-gas mixture, emerges. Another name for Trimix is "poor man's gas". As can be understood from this saying, the first problem of helium is cost.

Another problem with helium is that, contrary to popular belief, it prolongs deco times. A diver who doesn't know much about anything but likes to appear knowledgeable thinks that trimix or helium is used in deep dives because it shortens the deco time. However, helium penetrates the tissues much faster and the tissues reach saturation faster. Therefore, the helium deco is longer and the higher the helium ratio in the trimix mixture you will use, the longer the deco dives you will make. For this reason, we use nitrox mixtures with a high oxygen content as deco gas so that we can increase the pressure difference and release the gas as soon as possible without being exposed to helium and nitrogen, which are inert gases.

There are also two different disorders caused by helium, called HPNS and isobaric counter diffusion. HPNS, like oxygen poisoning, affects the nervous system when the partial pressure of helium increases too much. Isobaric counter diffusion is the specific name for inner ear decompression sickness that can occur when switching from a high helium density mixture to a high nitrogen density mixture. We will examine both disorders separately, but we can summarize them briefly as above and increase our diving depth to much deeper values ​​than air with trimix without getting these disorders.