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*NEWS* Photos Must See!
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Technical Scuba Diving and other interesting Articles The Pain Principle --- ‘Elements of extreme dive planning' ‘Nitrogen,
Helium and other hard drugs of the deep.’ Just like the properties of oxygen discussed in the previous article in this series, Nitrogen and Helium have some curious properties that make them both useful and deadly to deep divers. For extreme divers, the effects of the high ambient pressure increase the toxic effects of these gases so much as to cause unconsciousness or other debilitating effects within minutes, but there are some poorly understood side effects that open the doorway to achieving even greater depths down to 700meters/2,300foot and beyond... Give me the anti-dote! Although their usage has been banned in modern times, the use of chemical and biological agents to wage war has existed for centuries. In recent times, the use of highly toxic nerve agents such as Tabun and Sarin strike fear into the heart of even the most hardened combat soldier, who will drop everything to don his chemical warfare suit in the battlefield in the event of the chemical warfare alert being sounded. One way chemical warfare agents work is by attacking the body’s nervous systems so as to slow down the sufferer’s heart rate until death occurs. The antidote discovered involved administering a near lethal dose of the deadly poison atropine to a nerve agent victim, which would normally cause death by making the heart race too quickly, thus the effects of the nerve agent could be cancelled out. This leads us to understanding the important process, by which mixing different breathing gases together that both have toxic, but apposing symptoms at the ambient pressure under question, we can create a mixture where the different toxic effects of each gas cancel each other out. Deep Air effects- Narcosis or Anesthesia? Any person undergoing even basic diver training will be taught about the dangers of Nitrogen Narcosis that become progressively worse on descending past 30m/100ft. A common explanation for the effects of narcosis is to compare it to drinking Martini’s. Depending on whose ‘Martini-effect’ explanation is used, once past the starting point of 30m/100ft the narcotic effect is supposed to be equivalent to 1 martini on an empty stomach for every 15m/50ft deeper. So 45m/150ft will give narcosis equivalent to 1 martini …and 60m/200ft will be equivalent to 2 martinis etc. The ‘Martini effect’ is fun for describing narcosis to entry level divers since most adults can relate to the description. However the real effects of narcosis are far more dangerous since Nitrogen at high partial pressures behaves more like an anesthetic gas or the incapacitating ‘rave’ drug Ketamine Hydrochloride. Both numb your extremities, bring on drowsiness, then finally cause you to loose track of time and drift off to never-never land. It is NOT a good idea to have this happen on a deep dive. For the deep air diver with records reaching down to 150m/500ft, if Oxygen toxicity doesn’t trigger an early demise, then falling into deep anesthetic slumber from 12bars ppN2 will almost certainly result in a posthumous entry into the record books. Helium ‘Speed’
tremors-HPNS For relatively shallow extreme diving down to 150m/500ft, Helium is considered non narcotic. This rare and expensive gas finds use in Trimix (Oxygen/Helium/Nitrogen) and Heli-ox (Helium/Oxygen) mixtures in the 40m/130ft to 700m/1500ft range. Although the use of Trimix has been popularized by tech divers in recent years, apart from cost savings from not having to use so much helium as in the US$1 per breath Heliox, and slightly reduced decompression times for short duration technical dives, the use of Tri-mix for commercial diving would generally not be considered necessary until working at deeper than 150m/500ft where HPNS or High pressure nervous syndrome resulting from breathing Heliox starts to become a concern. HPNS manifests itself in all manner of physiological and psychological effects. The most obvious being ‘Helium Tremors’ where the hands or head shakes uncontrollably with symptoms similar to that of an amphetamine overdose. Conveniently, it appears that HPNS causes the opposite symptoms of Nitrogen Narcosis. From the opening paragraph on counteracting one poison with another, the stage is then set to use a breathing gas containing the necessary oxygen plus balanced amounts of Helium and Nitrogen as the diluent. This is real Trimix; not the cost cutting Trimix used on a 90meter/300ft wreck dive. Exactly how much Nitrogen is necessary though to compensate for the HPNS? This is determined by trial and error from large numbers of dexterity and mental agility tests carried out on divers in a hyperbaric research facility. A 5-10% in the breathing mix seams to works well with a 1m/3ft per minute descent rate. Just one fly in the Narcosis versus HPNS ointment. HPNS symptoms are dependent on compression rate. Commercial divers might spend a day pressurizing to 300m/1,000ft working depth; a tech diver will arrive there in just 12 minutes. To compensate for the extreme HPNS caused by a fast descent to 300m/1,000ft requires extreme narcosis as an antidote. In this case perhaps as much as 20% nitrogen will be used giving the equivalent narcotic effect of a 70m/230ft air dive. With no research to predict a happy outcome for Narcosis compensation of HPNS for the tech diver at these depths and descent rates, Gas choice for the deepest portion of the dive so as to remain alert, but with sufficiently suppressed HPNS to maintain dive discipline and essential gas management duties remains the real unknown for the deep explorer.
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