Asymptotic giant branch forming helium (known as hydrogen burning), and a very large envelope of material of composition similar to main-sequence stars. When a star exhausts the supply of hydrogen by nuclear fusion processes in its core, the core contracts and its temperature increases, causing the outer layers of the star to expand and cool. The star becomes a red giant, following a track towards the upper-right hand corner of the HR diagram. Eventually, once the temperature in the core has reached approximately , helium burning (fusion of helium nuclei) begins. The onset of helium burning in the core halts the star's cooling
Hydrogen sulfide sulfide solution. Hydrogen sulfide generated in this process is typically converted to elemental sulfur using the Claus Process. Hydrogen sulfide is a highly toxic and flammable gas (flammable range: 4.3–46%). Being heavier than air, it tends to accumulate at the bottom of poorly ventilated spaces. Although very pungent at first, it quickly deadens the sense of smell, so victims may be unaware of its presence until it is too late. For safe handling procedures, a hydrogen sulfide safety data sheet (SDS) should be consulted. Hydrogen sulfide is a broad-spectrum poison, meaning that it can poison several different systems in the