Helium (He) is the second lightest element (hydrogen being the lightest) with a gaseous specific gravity of 0.138.
It is a colourless, odourless, tasteless inert gas at room temperature and atmospheric pressure. Its boiling point is –452.1°F (–268.9°C) at atmospheric pressure. Helium is present in dry air at a concentration of 0.0005%. Its principal source is natural gas wells where the helium is extracted from the crude natural gas stream and purified. Helium can be stored and shipped either as a gas or a cryogenic liquid.
Helium is widely used as an inert gas in the arc welding process. Helium is also used as a carrier gas for gas chromatography. Also, its low specific gravity and non-flammability allow its use in lighter-than-air applications such as the filling of balloons and blimps. Mixtures of helium and oxygen are used as a breathing gas for deep-sea diving. Liquid helium is used in superconducting magnet applications, including magnetic resonance imaging (MRI).