Information AboutBreathing Gas |
| CATEGORIES ABOUT BREATHING GAS | |
| diving | |
|
A safe breathing gas has three essential features:
Most breathing gases are a mixture of oxygen and one or more inert gases. The techniques used to fill Diving Cylinder s with gases other than air are called Gas Blending . COMMON DIVING BREATHING GASES Common diving breathing gases are:
INDIVIDUAL COMPONENT GASES Oxygen Oxygen (O2) must be present in every breathing gas. This is because it is essential to the Human Body 's Metabolic Process , which sustains life. The human body cannot store oxygen for later use as it does with food. If the body is deprived of oxygen for more than a few minutes, unconsciousness results. The Tissues and Organ s within the body (notably the heart and brain) are damaged if deprived of oxygen for much longer than four minutes. The proportion of oxygen in a '''breathing gas''' determines the depth at which the mixture gas can safely be used:
The minimum safe Partial Pressure of oxygen in a breathing gas is 16 kPa (0.16 bar). Below this partial pressure the diver risks unconsciousness and death due to Hypoxia . When a hypoxic mix is breathed is shallow water it may not have a high enough ppO2 to keep the diver conscious. For this reason normoxic or hyperoxic "travel gases" are used at medium depth between the "bottom" and "decompression" phases of the dive. The maximum safe partial pressure of oxygen in a breathing gas depends on exposure time, but for dives of less than three hours is commonly considered to be 140 kPa (1.4 bar), although the U.S. Navy has been known to authorize dives with a partial oxygen pressure of as much as 180 kPa (1.8 bar). At high partial pressures or longer exposures, the diver risks oxygen toxicity including a Seizure similar to an epileptic fit. Each breathing gas has a Maximum Operating Depth that is determined by its oxygen content. Oxygen Analysers are used to measure the concentration of oxygen in the gas mix. Filling a diving cylinder with pure oxygen costs around five times more than filling it with compressed air. As oxygen supports combustion and causes rust in Diving Cylinder s, it should be handled with respect when Gas Blending . Divox "Divox" is Oxygen . In the Netherlands , pure oxygen for breathing purposes is regarded as medicinal as opposed to industrial oxygen, such as that used in Welding , and is only available on Medical Prescription . The diving industry "created" Divox and registered it as a Trademark to circumvent the strict rules concerning medicinal oxygen thus making it easier for (recreational) Scuba divers to obtain oxygen for blending their breathing gas. Nitrogen Nitrogen (N2) is an Inert Gas and the main component of Air , the cheapest and most common breathing gas used for diving. It causes Nitrogen Narcosis in the diver, so its use is limited to shallower dives. Nitrogen can cause Decompression Sickness . Equivalent Air Depth is often used to help design a breathing gas mix by determining the maximum nitrogen content for a particular depth of dive. Many divers find that the level of narcosis caused by a 30-metre (100-foot) dive, whilst breathing air, is a comfortable maximum. The partial pressure of nitrogen at this depth on air is 316 kPa (3.16 bar) (Fraction of nitrogen x absolute pressure = 0.79 x 400 kPa). So, what fraction of nitrogen would cause the same narcosis at 60 metres? The answer is 45% nitrogen. (316 kPa/700 kPa) Helium Helium (He) is an inert gas that is less narcotic than nitrogen at diving pressures, so it is more suitable for deeper dives than nitrogen. But helium can still cause Decompression Sickness . It also causes High Pressure Nervous Syndrome . It is not very suitable for Dry Suit inflation due to its poor thermal insulation properties — helium is a very good conductor of heat, but air is a rather poor conductor of heat. Helium fills typically cost ten times more than an equivalent air fill. Helium also distorts the diver's voice, which may impede communication. Neon Neon (Ne) is an inert gas sometimes used in deep Commercial Diving but is very expensive. Like helium, it is less narcotic than nitrogen, but unlike helium, it does not distort the diver's voice. Hydrogen Hydrogen (H2) has been used in deep diving gas mixes but is very explosive when mixed with more than about 4 to 5% oxygen (such as the oxygen found in breathing gas). This limits use of hydrogen to deep dives and complicated protocols to insure that oxygen is cleared from the lungs, the blood stream and the breathing equipment before breathing hydrogen starts. Like helium, it distorts the diver's voice. See 1 UNWELCOME COMPONENTS OF BREATHING GASES Many gases are not suitable for use in diving breathing gases. Here is an incomplete list of gases commonly present in a diving environment: Argon Argon (Ar) is an inert gas that is more narcotic than nitrogen, so is not suitable as a diving breathing gas. It is used for Dry Suit inflation because of its good thermal insulation properties. Argon is much more expensive than air. Carbon dioxide Carbon Dioxide (CO2) is produced by the Metabolism in the Human Body and causes Carbon Dioxide Poisoning . Carbon monoxide Carbon Monoxide (CO) is produced by incomplete Combustion . Two common sources are:-
It causes Carbon Monoxide Poisoning . Hydrocarbons Hydrocarbon s (CxHy) are present in compressor lubricants and Fuel s. They can enter diving cylinders as a result of contamination, leaks, or due to incomplete combustion near the air intake.
MOISTURE CONTENT The process of Compressing Gas into a diving cylinder removes moisture from the gas. This is good for Corrosion prevention in the cylinder but means that the diver inhales very dry gas. The dry gas extracts moisture from the divers lungs while underwater contributing to Dehydration , which is also thought to be a predisposing risk factor of Decompression Sickness . It is also uncomfortable, causing a dry mouth and throat and making the diver thirsty. This problem is reduced in Rebreather s because the Soda Lime reaction to remove carbon dioxide puts moisture back into the breathing gas. In hot, tropical climates, open circuit diving can accelerate Heat Exhaustion because of dehydration. GAS DETECTION AND MEASUREMENT Divers find it difficult to detect most gases that are likely to be present in diving cylinders because they are colourless, odourless and tasteless. Electronic sensors exist for some gases, such as Oxygen Analyser s, Helium Analyser , Carbon Monoxide Detector s and Carbon Dioxide Detector s. Oxygen analysers are commonly found underwater in Rebreather s. Oxygen and helium analysers are often used on the surface during Gas Blending . Chemical and other types of gas detection methods are not often used in diving. EXTERNAL LINKS |
|
|