Nitrogen-Caused Phenomena in Diving

Have you ever wondered how divers are able to dive so deep with little repercussions? Diving at its core, is a basic maneuver that many people can perform without tools. However, the perspective shifts when one intends to dive deeper. Deeper dives require divers to bring essential equipment, such as air tanks and goggles. However, this equipment is simple only in its rudimentary form. In reality, divers seeking to dive deep must bring many gas cylinders with different gasses based on their dive depth in order to avoid nitrogen narcosis, a temporary condition that can cause dangerous changes in consciousness and neuromuscular functionality. It often occurs due to nitrogen building up in the body faster than the body can absorb it (Kirkland et al., 2023). 

According to Boyle’s Law, which states that PV=K, which states that pressure multiplied by volume equals a constant K. The increase of pressure causes gas volume to decrease, therefore increasing the density of the gas. This means the effects of gasses grow relative to the pressure increase caused by the depth. At a depth of ten meters, the effect of gasses will double, at twenty meters, it will triple, and so on (NOAA, 2019). Therefore, the deeper a diver goes, the more nitrogen they will breathe in. The nitrogen eventually becomes too much for the body to absorb, resulting in nitrogen narcosis. When diving, the total pressure of gas increases by one atmospheric pressure (atm) every ten meters. Total gas pressure is the pressure that the gas compound exerts. When discussing the pressure exerted by one gas exclusively in a compound of gasses, scientists refer to it as the partial pressure of the gas. This means that, according to Dalton’s Law of Partial Pressures, the increasing total pressure of a mixture results in the increase of the partial pressure of each gas it contains. Nitrogen causes narcosis after a partial pressure of three atm, and oxygen is toxic above a partial pressure of 1.4 atmospheres, meaning that hypothetically, a 100% nitrogen mixture will become toxic at twenty meters deep (disregarding breathability) and a 100% oxygen mixture will become toxic at four meters deep (14.14: Dalton’s Law of Partial Pressures, n.d.).

When first entering the water, divers use tanks of compressed air to breathe. Compressed air is made of about 79% nitrogen and 21% oxygen (with traces of other gasses). However, due to the narcotic effect of nitrogen, a diver is forced to decrease nitrogen intake by using gasses with a lower concentration of nitrogen to be able to go deeper.

Once a diver reaches a depth of 38 meters, nitrogen levels should be reduced to prevent the increasingly narcotic nitrogen from causing nitrogen narcosis. To do this, divers at this depth switch to Nitrox, which is again a mixture of nitrogen and oxygen, but this time include less 78% nitrogen, though more commonly contain 64-68% nitrogen (“Probing the Limits of Human Deep Diving,” 1984). With a lower concentration of nitrogen, the effect of narcotic nitrogen is further reduced. Oxygen toxicity, harmful effects on the body caused by breathing oxygen at high pressures, can become a worry at a depth of about forty meters. After this depth, a diver should switch gasses once again in order to continue a safe journey (Wilmshurst, n.d.).

Trimix is a breathing gas that also increases nitrogen and oxygen, similar to its counterparts Nitrox and compressed air. However, it also includes another gas, helium. It is most commonly composed of 21% oxygen, 44% nitrogen, and 35% helium, but Trimix compositions vary significantly. Since many Trimix mixtures use oxygen percentages below the normal survivability level for humans, Trimix should only be used starting at various depths depending on the mixture used (Dive SAGA - Scuba diving, 2023). 

Decompression sickness (DCS), is another diving phenomenon that can cause effects similar to that of nitrogen narcosis. Decompression sickness occurs during the ascension part of the dive when the nitrogen absorbed by the body during descent floods too quickly into the bloodstream, clotting it (Harvard Health Publishing). Divers avoid this by making decompression stops along the ascent. When a diver is at the bottom of their dive, every minute spent at the bottom increases their decompression time by four minutes. Therefore, divers must bring extra gasses to support themselves throughout the decompression.

Although nitrogen narcosis and DCS can occur at various depths depending on what gas is used, some divers may have some natural resistance to these effects. One example of this phenomenon is Sheck Exley. Sheck Exley was a scuba diver in the late 20th century who had an unusual resistance to nitrogen narcosis. Due to this extraordinary resistance, he was able to dive 120 meters using only compressed air. Sheck is one of only a few divers who has ever accomplished this feat (Sheck Exley: A Cave Diving Pioneer, 2016).

In practice, divers often use a number of different tactics to avoid oxygen toxicity, DCS, and nitrogen narcosis. Often used in cave diving or other situations where a direct ascent is not possible, one of these methods is known as the rule of thirds. The rule of thirds is a practice involving using one third of a divers gas reserve on the way down, one third on the way back to the surface, and saving the last third for reserve in case of emergency. Another technique used to prevent these conditions is by using safety stops. Safety stops are gas cylinders placed at specific places throughout the dive which assist by acting as decompression stops as the diver ascends at the end of the dive, which often takes hours (Suzee Skwiot, 2023). Another important reason why divers use this method is to decrease weight. While increased weight initially helps with a quick and easy descent, the diver must leave some gas cylinders at decompression stops to ensure an easy ascent.

Ultimately, while diving may seem like a simple task, there are numerous different obstacles that a diver must overcome to reach deep depths when diving. While a quick dip in the water will not need any complicated gas, it is important to distinguish what types of gasses may be needed in order to stay safe at deeper depths.

References

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