The development of any replacement technology for helium is problematic because its use is based on its combination of unique size and inertness. Inert gases other than argon, which is excluded because it exists in the atmosphere at the 1 percent level, could be used in principle, but comparable sensitivity might require more elaborate mass spectrometers than are currently employed in helium leak-detection systems. Some degree of conservation through gas recovery might be possible using ''sniffer" technology. In this approach, helium is introduced under pressure into the device being tested, and a sniffer, connected to a helium-tuned mass spectrometer, detects leaks by sensing helium leaking out of the helium-pressurized apparatus. Helium used in this manner could be recovered.

Breathing Mixtures

Mixtures of helium and oxygen are used as breathing gases for deep-sea divers and for individuals working under high atmospheric pressures for extended periods of time. The advantage of helium over nitrogen in these mixtures is that it is absorbed and released by human tissue faster than nitrogen, making longer dives possible with shorter decompression times. The amount of helium used was about 56 million scf (1.6 million scm) in 1996. Given the diving industry's increasing reliance on robot replacements for humans, however, the amount of helium used for diving is expected to remain relatively stable, or even decline. Each dive consumes very little helium because "rebreathers," which recirculate the gas, are commonly employed.

Lifting

One obvious use of helium is as a lifting gas. Unfortunately, this usage is no longer reported separately, making the amount of helium used for this purpose unknown. Because it is the most visible use of helium, however, it deserves mention in a separate section of this report.

Hydrogen is the lightest gas, but helium's chemical inertness makes it the safest lifting gas. Helium replaced hydrogen for blimps in the 1930s after a number of tragic accidents involving hydrogen-filled airships. Nowadays, party balloons are probably the application with which most people are familiar. Helium is used as well in blimps that bear advertising (e.g., the Goodyear blimp), to detect low-flying cruise missiles, and to carry radar equipment to detect drug smugglers along the nation's borders. Helium-filled balloons are also used in various types of atmospheric and astrophysical research. One future use of helium is as a lifting gas in devices to lift heavy loads for construction.

Other Uses of Helium

Other uses of helium include minor medical uses and uses in lasers not covered in previous sections. The total amount of helium used for these purposes was about 320 million scf (8.9 million scm) in 1996.



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