Helium breathing

The quantity of breathing gas consumed in deep dives is of both economical and logistical concern at depths of 300 m, a reasonably active diver requites ca 1.8 m (64 fT at STP) of breathing gas per minute. In closed-cycle breathing systems, of both the self-contained and umbiHcal types, the helium is recitculated after carbon dioxide is removed and the oxygen replenished (147). 

The low breathing resistance of helium—oxygen mixtures is of therapeutic advantage for patients suffering from asthma and other obstmctive respitatory difficulties. The mixtures have also been used for hyperbaric therapy. 

Helium, the first member of the group, was detected in the spectrum of the Sun in 1868. Because of its low density (7 that of air), helium is used in all kinds of balloons and in synthetic atmospheres to make breathing easier for people suffering from emphysema. 

Another consequence of the effect of pressure on gas solubility is the painful, sometimes fatal, affliction known as the bends. This occurs when a person goes rapidly from deep water (high pressure) to the surface (lower pressure), where gases are less soluble. The rapid decompression causes air, dissolved in blood and other body fluids, to bubble out of solution. These bubbles impair blood circulation and affect nerve impulses. To minimize these effects, deep-sea divers and aquanauts breathe a helium-oxygen mixture rather than compressed air (nitrogen-oxygen). Helium is only about one-third as soluble as nitrogen, and hence much less gas comes out of solution on decompression. 

Which difference could account for the fact that a diver is much less likely to suffer from the bends if he breathes a mixture of 80% helium and 20% oxygen than if he breathes air (The bends is a painful, sometimes fatal, disease caused by the formation of gas bubbles in the veins and consequent interruption of blood flow. The bubbles form from gas dissolved in the blood at high pressure.)... 

Elements and compounds constitute the world of pure substances. An element is a substance that cannot be decomposed by any chemical reaction into simpler substances. Elements are composed of only one type of atom and all atoms of a given type have the same properties. Pure substances cannot be separated into other kinds of matter by any physical process. We are familiar with many pure substances water, iron, mercury, iodine, helium, rust, diamond, table salt, sugar, gypsum, and so forth. Among the pure substances listed above, iron, mercury, iodine, diamond (pure carbon), and helium are elements. We are also familiar with mixtures of pure substances. These include the air that we breathe, milk, molasses, beer, blood, coffee, concrete, egg whites, ice cream, dirt, steel, and so on. 

It is the oxidizer for liquid rocket fuels, and as a gas, oxygen is used in a mixture with helium to support the breathing of astronauts and divers and to aid patients who have dif-flculty breathing. It is use to treat (oxidize) sewage and industrial organic wastes. 

Researchers found an increase in volume of isoflow, a decrease in change in flow while breathing helium compared to air at 50% vital capacity, and the continued presence of abnormal chest radiographs. The study suggests that there may be long-term respiratory effects following aspiration of ingested kerosene. 

We are thus able to reconstruct the Sun s whole career, from its nebulous birth, through its first nuclear reaction, right up to its last breath as a red giant. We may watch it swell up proudly as it burns its first helium, then throw its envelope off a hot, dense core, before the latter grows rigid, becoming a white dwarf, frozen in crystal. Wonders But let us recall the vast effort that went into this undertaking. 

Helium None known Used to replace nitrogen as an 02 diluent in breathing mixtures to prevent the bends in high-pressure work. 

Helium To provide an inert atmosphere for welding As a coolant in nuclear reactors With 20% oxygen, as a breathing gas for deep-sea divers To inflate the tyres of large aircraft To fill airships and weather balloons (Figure 11.12) In the helium-neon laser In low-temperature research, because of its low boiling point... 

The panels in the first and last columns in Figure 5.11 correspond to two selected consecutive times at which a wave front originates close to the nucleus, 14.51 and 15.63 fs, while the central column corresponds to a time halfway between these two. In the upper row of Figure 5.11, we show the electron density within 15 Bohr radii from the nucleus its breathing motion is evident At f = 14.51 fs (a) the central part of the wave packet is at the peak of its contraction. At f = 15.09 fs (b) it reaches its maximal expansion. Finally, at f = 15.63 fs (c), it is contracted again. Thus, the relation between the breathing of the electron density at small radii and the ejection of isolated electron density bursts is more subtle than the obvious correspondence between their periodicities. Indeed, the instants at which the wave fronts are born in the vicinity of the nucleus correspond closely to the stages of maximum contraction of the localized part of the metastable wave packet. This evidence supports the idea that the collisional description of the autoionization dynamics of the doubly excited state of helium holds down to the least excited ones. 

Figure 5.14 The helium ionization yield for the ion being left in the He+(2s) and He+(2p) excited states as a function of the time delay between the initial XUV pump pulse and the IR probe pulse. The oscillations are due to breathing between different doubly excited states (resonances).

The gas is also used to fill balloons, in gas discharge lamps, and as an additive in the breathing gases of astronauts and scuba divers. The rarer stable isotope of helium (3He) is produced by the decay of radioactive tritium, and is used in resonance imaging and in the attainment of very low temperatures, about 0.010 kelvin, via a process known as dilution refrigeration. see also Noble Gases Nuclear Fusion. 

Do not breathe too close to the sniffing probe or its reference chamber because the C02 from your breath could cause a deflection of the needle. If you are going to use a helium test gas after doing a bubble test, you must wait until the system is completely dry. The water will cause a negative deflection and the helium will cause a positive deflection, providing a combined weaker deflection. If, coincidentally, the water and helium are perfectly balanced, there will be no deflection. 

Helium is used for filling balloons and dirigibles and for mixing with oxygen (in place of the nitrogen of the air) for breathing by divers, in order to avoid the bends, which are caused by gas bubbles... 

Helium-laced gases are used as breathing media for deep-sea divers. Why Table 10.1 may provide useful data. 

Breathing heliox also affects the voice. Helium is much less dense than nitrogen, so vocal cords vibrate faster in a heliox atmosphere. This raises the pitch of the diver s voice, and makes the diver s voice sound funny. Fortunately, this effect disappears when the diver surfaces and begins breathing air again. 

---