Hydreliox is an exotic

breathing gas A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed h ...

mixture of

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. It ...

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well ...

and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxi ...

. For the Hydra VIII (Hydra 8) mission at 50 atmospheres of ambient pressure, the mixture used was 49% hydrogen, 50.2% helium, and 0.8% oxygen. It is used primarily for research and scientific

deep diving Deep diving is underwater diving to a depth beyond the norm accepted by the associated community. In some cases this is a prescribed limit established by an authority, while in others it is associated with a level of certification or training, an ...

, usually below . Below this depth, extended breathing of

heliox Heliox is a breathing gas mixture of helium (He) and oxygen (O2). It is used as a medical treatment for patients with difficulty breathing because mixture generates less resistance than atmospheric air when passing through the airways of the lung ...

gas mixtures may cause

high pressure nervous syndrome High-pressure nervous syndrome (HPNS – also known as high-pressure neurological syndrome) is a neurological and physiological diving disorder which can result when a diver descends below about using a breathing gas containing helium. The eff ...

(HPNS). Two gas mixtures exist that attempt to combat this problem: trimix and hydreliox. Like trimix, hydreliox contains helium and oxygen and a third gas to counteract HPNS. The third gas in trimix is

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at sevent ...

and the third gas in hydreliox is

. Because hydrogen is the lightest gas, it is easier to breathe than

under high pressure. To avoid the risk of explosion, as a rule of thumb hydrogen is only considered for use in breathing mixtures if the proportion of oxygen in the mixture is less than 5%. However, the pressure during the dive must be such that the

partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas ...

of 5% oxygen is sufficient to sustain the diver. (The flammability of the mixture also depends to some degree on the pressure) The diving depth record for off-shore (saturation) diving was achieved in 1988 by a team of

professional diver Professional diving is underwater diving where the divers are paid for their work. The procedures are often regulated by legislation and codes of practice as it is an inherently hazardous occupation and the diver works as a member of a team. D ...

s (Th. Arnold, S. Icart, J.G. Marcel Auda, R. Peilho, P. Raude, L. Schneider) of the Comex S.A., industrial deep-sea diving company performing pipe line connection exercises at a depth of of seawater ( msw/fsw) in the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...

as part of the Hydra VIII (Hydra 8) programme. Hydreliox has been tested in 1992 to a simulated depth of by COMEX S.A. diver Théo Mavrostomos in an on-shore

hyperbaric chamber A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of ...

as part of the Hydra X (Hydra 10) programme. The diver stayed only a few hours at the simulated depth, and took 43 days to complete the record experimental dive. Although breathing hydreliox improves the symptoms seen in HPNS, tests have shown that

hydrogen narcosis Hydrogen narcosis (also known as the hydrogen effect) is the psychotropic state induced by breathing hydrogen at high pressures. Hydrogen narcosis produces symptoms such as hallucinations, disorientation, and confusion, which are similar to hall ...

becomes a factor at depths of .COMEX PRO
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References

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See also

References