What is helium gas used for? MRI magnets leak detection, lifting, welding, diving and why every litre must be conserved

Helium is bought for four properties no other gas combines: the lowest boiling point in nature, −268.93 °C; the second-lowest density; a thermal conductivity nearly six times that of air; and total chemical inertness in a very small atom. It cannot be made, cannot be recovered from air at 5.2 ppm, and once vented it rises out of the atmosphere for good. Every use below therefore sits beside a question about recovery, and the helium supply and conservation page should be read with this one.

The largest single use of helium is as the liquid that keeps superconducting magnets cold. Niobium-titanium wire, the conductor in nearly every MRI scanner, superconducts only below about 9 K and is operated at 4.2 K, the boiling point of helium at atmospheric pressure. Nothing else is liquid at that temperature. A hospital MRI holds its coil in a helium bath inside a vacuum-insulated cryostat; a new installation takes on the order of 1,500 litres of liquid helium, and older machines boil off a few hundred litres a year that must be replaced. Modern "zero boil-off" designs recondense the vapour with a cryocooler and need only occasional top-up, and the newest sealed systems hold a few litres, but the installed base in India is overwhelmingly bath-cooled.

The same physics serves NMR spectrometers in pharmaceutical and university laboratories, the superconducting magnets of particle accelerators, magnetic separation in kaolin and mineral processing, and the cryopumps and dilution refrigerators of low-temperature research. Liquid helium is also the only way to reach the temperatures at which quantum computers and infrared space telescopes operate.

Helium's small atomic size and inertness make it the tracer gas of choice for leak testing. A vessel, heat exchanger, vacuum chamber, refrigeration circuit, car air-conditioner, fuel tank or pacemaker is filled with helium or placed in a helium atmosphere, and a mass spectrometer tuned to mass 4 detects what escapes. Because air contains only 5.2 ppm helium the background is near zero, and because helium diffuses faster than any gas except hydrogen the response is fast. Sensitivity reaches about 10⁻¹² mbar·L/s, several orders of magnitude below pressure-decay or bubble testing. Automotive, refrigeration, aerospace and pharmaceutical container lines run helium leak test stations as a routine step, usually with a recovery system because the gas is reused many times.

Heat transfer uses helium's high thermal conductivity, the highest of any gas except hydrogen. Helium is the quench gas in vacuum heat-treatment furnaces, where it cools the charge faster than nitrogen at the same pressure; it fills the gap between silicon wafers and their chucks to carry heat in plasma etching tools; and it was the coolant of high-temperature gas-cooled nuclear reactors because it is inert, transparent to neutrons and does not become radioactive.

Helium at 0.169 kg/m³ at 15 °C lifts about 1.05 kg per cubic metre of displaced air at sea level, about 8 % less than hydrogen, with none of the fire risk. Weather-sounding balloons, scientific high-altitude balloons, advertising blimps, tethered surveillance aerostats and party balloons all use it. Party balloons are the use most often criticised, because the gas is vented to the atmosphere within a day; several national associations and suppliers have asked that balloon helium be the first use curtailed in a shortage, and balloon grade is deliberately the lowest purity sold.

Source: densities from the NIST Chemistry WebBook and the standard atmosphere; lift is the density difference.

Helium is an inert shielding gas like argon, but the arc it carries behaves differently. Its ionisation energy of 24.59 eV, against 15.76 eV for argon, raises the arc voltage at a given current, so the arc delivers more heat into the joint. That is wanted on thick aluminium and copper, which conduct heat away so fast that an argon arc struggles to form a pool, and in mechanised and high-speed TIG where helium raises travel speed. Helium also gives a flatter, wider bead with less porosity on aluminium. Against this, the arc is harder to start, the gas floats upwards off the pool so flow rates must be two to three times those of argon, and the cost is many times higher. In practice welders use argon-helium mixtures from 25 to 75 % helium and reserve pure helium for the heaviest non-ferrous work, laser welding where its high ionisation potential suppresses plasma formation above the keyhole, and some orbital pipe welding. The comparison with KIGL argon is set out on choosing a shielding gas.

Nitrogen breathed under pressure below about 40 to 50 m produces narcosis, and its density makes breathing laborious. Commercial and technical divers replace it with helium: heliox (helium and oxygen) and trimix (helium, oxygen and nitrogen) remove the narcosis and cut gas density, allowing saturation diving to 300 m and beyond. The penalties are the high-pitched voice, which saturation systems correct electronically, and rapid heat loss, because the same thermal conductivity that makes helium a good coolant strips heat from the diver's lungs; divers breathing helium at depth use heated gas. In hospitals heliox, usually 79 % helium, is given to patients with severe airway obstruction because its low density reduces the work of breathing, and helium-oxygen is used in some lung-function tests.

Helium is a by-product of natural gas, concentrated by radioactive decay of uranium and thorium in certain rock formations and trapped with the gas. Fields worth processing hold from about 0.3 % to a few per cent helium; the United States, Qatar, Algeria and Russia dominate production, and India has no producing field and imports its requirement. Prices have risen sharply through the shortages of the last fifteen years, and that has changed how the gas is used: MRI makers moved to zero-boil-off cryostats, leak-test stations recover and recycle, laboratories switched carrier gases, and large users install recovery compressors. For a user in India the practical rules are to buy the lowest grade the application tolerates, to recover from any process that releases more than a few cubic metres a month, and to treat cylinder leaks as a loss of a non-renewable resource rather than a nuisance.

Helium is supplied in seamless steel cylinders at 150 to 200 bar, in bundles, in tube trailers and as liquid in vacuum-insulated dewars at 4.2 K. A 46.7 litre cylinder at 150 bar holds about 6.5 m³ at 15 °C, a little less than the ideal 7.0 m³ because helium's compressibility factor at that pressure is about 1.07; the method is on gas cylinder sizes and contents in India. Cylinders are painted middle brown (shade 411) under IS 4379:2021, carry UN 1046, and need no PESO storage licence up to 200 cylinders of non-flammable non-toxic gas (Gas Cylinders Rules 2016, rule 44(b)(ii)). The Indian specification is IS 15583, Compressed helium gas, first issued in 2005 and revised in 2026; KIGL publishes its grades as its own specifications until the revised text is held. KIGL helium grades, and the inert-gas hazards that apply to it, are on the product page and on helium safety data explained; the transport and first-aid detail is on the helium safety data sheet.