Helium is used for many purposes that require some of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, or inertness. Of the 2008 world helium total production of about 32 million kg (193 million standard cubic meters) helium per year, the largest use (about 22% of the total in 2008) is in cryogenic applications, most of which involves cooling the superconducting magnets in medical MRI scanners. Other major uses (totalling to about 78% of use in 1996) were pressurizing and purging systems, maintenance of controlled atmospheres, and welding. Other uses by category were relatively minor fractions. Controlled atmosphere Helium MRI Helium gas arc welding helium leak detection helium flight gas helium diving gas