The remnants of decomposed phytoplankton and algae, pressurized and heated on the seafloor, petroleum makes up over one-third of the total energy used in the United States. The majority is consumed as gasoline by automobiles. Second is distillate fuel oil, in the form of diesel fuel and fuel oils.
ASTM D396-21: Standard Specification for Fuel Oils sets various grades of fuel oil.
Fuel Oil Grades in ASTM D396
Fuel oils are used primarily for space heating and electric power generation. According to ASTM D396-21, there are the following fuel oil grades:
- No. 1 S5000
- No. 1 S500
- No. 1 S15
- No. 2 S5000
- No. 2 S500
- No. 2 S15
- Grades B6-B20 S5000
- Grades B6-B20 S500
- Grades B6-B20 S15
- No. 4 (Light)
- No. 4
- No. 5 (Light)
- No. 5
- No. 6
The nomenclature of these closely parallels that of diesel fuels, as established by ASTM D975-20. This includes maximum sulfur content, meaning that No. 1 S15 contains no greater than 15 ppm sulfur. Heating oils and other oil fuels with less sulfur emit less of the element into the atmosphere when burned, and are thus cleaner. Because of this, many states have limited the amount of allowable sulfur in heating oils.
No. 1 Fuel Oil (Light Distillate Fuel)
No. 1 fuel oil is a light distillate fuel chemically comparable to kerosene. Its common applications are for portable outdoor stoves and portable outdoor heaters.
No. 2 Fuel (Heating Oil)
No. 2 fuel is what we commonly call “heating oil,” meaning that it is used in atomizing type burners for domestic heating.
While No. 2 fuel does moderately comprise some of the fuel oil used for industrial purposes, this duty is generally that of higher grades.
No. 6 Fuel (Residual Fuel Oil or Heavy Fuel Oil)
Grade No. 6 fuels, also known as residual fuel oil (RFO) or heavy fuel oil (HFO), are the remainder of the crude oil after gasoline and distillate fuel oils have been extracted through distillation. It is used to fuel robust engines.
Fuel Blends (Grades No. 4 and No. 5)
Grades No. 4 and No. 5 are mixtures of No. 2 and No. 6. Heavy distillate fuels or middle distillate/residual fuel blends comprise the No. 4 fuels. They are used in commercial or industrial burners that have been equipped for the appropriate viscosity range. No. 5 fuels are of greater viscosity, and they are generally composed of 75% to 80% of No. 6 and 25% to 20% of No. 2.
Fuel oils with grades B6-20 are middle distillate fuel blended with biodiesel. Biodiesel blends are given the abbreviation BXX, in which XX represents the volume percentage of biodiesel in the blend (6 to 20%). They are used in domestic and small industrial burners.
About ASTM D396-21
ASTM D396-21 is intended to be used by purchasing agencies in formulating specifications included in contracts for purchases of fuel oils and for the guidance of customers in selecting fuel oils. However, it should not preclude the observance of regulations. The document includes guidelines on the grades, test methods, and supplementary information for sulfur test methods, transfer conditions, evaluating new materials, and tenth percentile minimum ambient air temperatures in U.S. states.
Please refer to our article ASTM Diesel Fuel Oils Standard Specification for information on diesel fuel.
ASTM D396-21: Standard Specification for Fuel Oils is available on the ANSI Webstore.