Liquid helium Liquid helium At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temperature of −270 °C (about 4 K or −452.2 °F). Its boiling point and critical point depend on which isotope of helium is present: the common isotope helium-4 or the rare isotope helium-3. These are the only two stable isotopes of helium. See the table below for the values of these physical quantities. The density of liquid helium-4 at its boiling point and a pressure of one atmosphere (101.3 kilopascals) is about 0.125 grams per cm, or about 1/8th the density
Lowest-observed-adverse-effect level LOAEL refers to a dose of chemical that is ingested, while a LOAEC refers to direct exposure to a chemical (e.g., through gills or the skin). Lowest-observed-adverse-effect level The lowest-observed-adverse-effect level (LOAEL) is the lowest concentration or amount of a substance found by experiment or observation that causes an adverse alteration of morphology, function, capacity, growth, development, or lifespan of a target organism distinguished from normal organisms of the same species under defined conditions of exposure. Federal agencies use set approval standards below this level. The United States Environmental Protection Agency defines LOAEL as the 'lowest level of a chemical