Heating oil is any petroleum product or other oil used for heating; a fuel oil. Most commonly, it refers to low viscosity grades of fuel oil used for furnaces or boilers use for home heating and in other buildings. Home heating oil is often abbreviated as HHO. Most heating oil products are chemically very similar to diesel fuel used as motor fuel; motor fuel is typically subject to higher fuel taxes. Many countries add fuel dyes to heating oil, allowing law enforcement to check if a driver is evading fuel taxes. Since 2002, Solvent Yellow 124 has been added as a "Euromarker" in the European Union; untaxed diesel is known as "red diesel" in the United Kingdom. Heating oil is commonly delivered by tank truck to residential, commercial and municipal buildings and stored in above-ground storage tanks ("ASTs") located in the basements, garages, or outside adjacent to the building. It is sometimes stored in underground storage tanks (or "USTs") but less often than ASTs. ASTs are used for smaller installations due to the lower cost factor. Heating oil is less commonly used as an industrial fuel or for power generation. Leaks from tanks and piping are an environmental concern. Various federal and state regulations are in place regarding the proper transportation, storage and burning of heating oil, which is classified as a hazardous material (HazMat) by federal regulators. Technical Characteristics Heating oil consists of a mixture of petroleum-derived hydrocarbons in the 14- to 20-carbon atom range that condense between during oil refining. Heating oil condenses at a lower temperature than petroleum jelly, bitumen, candle wax, and lubricating oil, but at a higher temperature than kerosene, which condenses between . The heavy (C20+) hydrocarbons condense between . Heating oil produces to and weighs 8.2 pounds per US gallon (0.95 kg/L). Number 2 fuel oil has a flash point of . Historically, the legal difference between diesel and heating oil in the United States has been sulfur allowance. Diesel for machinery and equipment must be below 15 ppm sulfur content while heating oil needed only stay below 500 ppm sulfur. However, most heating oil in the United States is now "ultra-low sulfur heating oil" (ULSHO) and meets the same 15 ppm standard. United States and Canada Heating oil is known in the United States as No. 2 heating oil. In the U.S., it must conform to ASTM standard D396. Diesel and kerosene,