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{{Use dmy dates|date=July 2019}}{{Redirect|Bunker oil|the Norwegian company|Bunker Oil (company)}}{{short description|Fuel oils of a tar-like consistency}}(File:Residual fuel oil.JPG|thumb|400x400px|Tar-like consistency of heavy fuel oil)Heavy fuel oil (HFO) is a category of fuel oils of a tar-like consistency. Also known as bunker fuel, or residual fuel oil, HFO is the result or remnant from the distillation and cracking process of petroleum. For this reason, HFO is contaminated with several different compounds including aromatics, sulfur, and nitrogen, making emissions upon combustion more polluting compared to other fuel oils.JOURNAL, McKee, Richard, Reitman, Fred, Schreiner, Ceinwen, White, Russell, Charlap, Jeffrey, O'Neill, Thomas, Olavsky Goyak, Katy, 2013, The toxicological effects of heavy fuel oil category substances, International Journal of Toxicology, 33, 1 Suppl, 95–109, 10.1177/1091581813504230, 24179029, HFO is predominantly used as a fuel source for marine vessel propulsion using marine diesel engines due to its relatively low cost compared to cleaner fuel sources such as distillates.JOURNAL, Bengtsson, S., Andersson, K., Fridell, E., 2011-05-13, A comparative life cycle assessment of marine fuels: liquefied natural gas and three other fossil fuels, Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment, en, 10.1177/1475090211402136, 110498596, JOURNAL, DeCola, Elise, Robertson, Tim, July 2018, Phasing Out the Use and Carriage for Use of Heavy Fuel Oil in the Canadian Arctic: Impacts to Northern Communities,weblink Report to WWF Canada, The use and carriage of HFO on-board vessels presents several environmental concerns, namely the risk of oil spill and the emission of toxic compounds and particulates including black carbon. The use of HFOs is banned as a fuel source for ships travelling in the Antarctic as part of the International Maritime Organization's (IMO) International Code for Ships Operating in Polar Waters (Polar Code).WEB,weblink Polar Code, www.imo.org, 2019-03-05, 10 April 2019,weblink" title="web.archive.org/web/20190410120131weblink">weblink dead, For similar reasons, an HFO ban in Arctic waters is currently being considered.MEPC 72 (2018). Report of the Marine Environment Protection Committee on its Seventy-Second Session.

Heavy fuel oil characteristics

HFO consists of the remnants or residual of petroleum sources once the hydrocarbons of higher quality are extracted via processes such as thermal and catalytic cracking. Thus, HFO is also commonly referred to as residual fuel oil. The chemical composition of HFO is highly variable due to the fact that HFO is often mixed or blended with cleaner fuels; blending streams can include carbon numbers from C20 to greater than C50. HFOs are blended to achieve certain viscosity and flow characteristics for a given use. As a result of the wide compositional spectrum, HFO is defined by processing, physical and final use characteristics. Being the final remnant of the cracking process, HFO also contains mixtures of the following compounds to various degrees: "paraffins, cycloparaffins, aromatics, olefins, and asphaltenes as well as molecules containing sulfur, oxygen, nitrogen and/or organometals". HFO is characterized by a maximum density of 1010 kg/m3 at 15°C, and a maximum viscosity of 700 mm2/s (cSt) at 50°C according to ISO 8217.WEB,weblink HFO, powerplants.man-es.com, 2019-04-07,

Combustion and atmospheric reactions

Given HFO elevated sulfur contamination (maximum of 5% by mass), the combustion reaction results in the formation of sulfur dioxide SO2.

Heavy fuel oil use and shipping

Since the middle of the 20th century,WEB,weblink History and Transition of Marine Fuel, 16 January 2024, Mitsui O.S.K. Lines (MOL) Group, WEB,weblink Marine Heavy Fuel Oil (HFO) For Ships – Properties, Challenges and Treatment Methods, 16 January 2024, Marine Insight, HFO has been used primarily by the shipping industry due to its low cost compared with all other fuel oils, being up to 30% less expensive, as well as the historically lax regulatory requirements for emissions of nitrogen oxides (NOx) and sulfur dioxide (SO2) by the IMO. For these two reasons, HFO is the single most widely used engine fuel oil on-board ships. Data available until 2007 for global consumption of HFO at the international marine sector reports total fuel oil usages of 200 million tonnes, with HFO consumption accounting for 174 million tonnes. Data available until 2011 for fuel oil sales to the international marine shipping sector reports 207.5 million tonnes total fuel oil sales with HFO accounting for 177.9 million tonnes.WEB,weblink Third IMO Greenhouse Gas Study 2014, 2014, 9 April 2019, 19 October 2015,weblink" title="web.archive.org/web/20151019064411weblink">weblink dead, Marine vessels can use a variety of different fuels for the purpose of propulsion, which are divided into two broad categories: residual oils or distillates. In contrast to HFOs, distillates are the petroleum products created through refining crude oil and include diesel, kerosene, naphtha and gas. Residual oils are often combined to various degrees with distillates to achieve desired properties for operational and/or environmental performance. Table 1 lists commonly used categories of marine fuel oil and mixtures; all mixtures including the low sulfur marine fuel oil are still considered HFO.{| class="wikitable"|+Table 1: Types of Marine HFO and Composition!Category of Marine HFO!Marine HFO Composition|Bunker C/Fuel oil No.6|residual oil|Intermediate Fuel Oil (IFO) 380|distillate combined with 98% residual oil|Intermediate Fuel Oil (IFO) 180|distillate combined with 88% residual oil|Low Sulfur Marine Fuel Oils (HFO derivative)|distillate/residual oil blend (higher ratio of distillate)

Arctic environmental concerns

(File:Oiled Black Bird.jpg|alt=|thumb|352x352px|Wildlife suffering from a tanker oil spill. Tar-like HFO coats and persistently sticks to feathers.)The use and carriage of HFO in the Arctic is a commonplace marine industry practice. In 2015, over 200 ships entered Arctic waters carrying a total of 1.1 million tonnes of fuel with 57% of fuel consumed during Arctic voyages being HFO.JOURNAL, Prior, Sian, Walsh, Dave, 2018-11-02, A Vision for a Heavy Fuel Oil-Free Arctic, Environment: Science and Policy for Sustainable Development, 60, 6, 4–11, 10.1080/00139157.2018.1517515, 158679052, 0013-9157, In the same year, trends in carriage of HFO were reported to be 830,000 tonnes, representing a significant growth from the reported 400,000 tonnes in 2012. A report in 2017 by Norwegian Type Approval body Det Norske Veritas (DNV GL) calculated the total fuel use of HFO by mass in the Arctic to be over 75% with larger vessels being the main consumers. In light of increased area traffic and given that the Arctic is considered to be a sensitive ecological area with a higher response intensity to climate change, the environmental risks posed by HFO present concern for environmentalists and governments in the area.JOURNAL, Willis, Kathy J., Benz, David, Long, Peter R., Macias-Fauria, Marc, Seddon, Alistair W. R., 2016, Sensitivity of global terrestrial ecosystems to climate variability, Nature, en, 531, 7593, 229–232, 10.1038/nature16986, 26886790, 1476-4687, 2016Natur.531..229S, 1956/16712, 205247770, free, The two main environmental concerns for HFO in the Arctic are the risk of spill or accidental discharge and the emission of black carbon as a result of HFO consumption.

Environmental impacts of heavy fuel oil spills

Due to its very high viscosity and elevated density, HFO released into the environment is a greater threat to flora and fauna compared to distillate or other residual fuels. In 2009, the Arctic Council identified the spill of oil in the Arctic as the greatest threat to the local marine environment. Being the remnant of the distillation and cracking processes, HFO is characterized by an elevated overall toxicity compared to all other fuels. Its viscosity prevents breakdown into the environment, a property exacerbated by the cold temperatures in the Arctic resulting in the formation of tar-lumps, and an increase in volume through emulsification. Its density, tendency to persist and emulsify can result in HFO polluting both the water column and seabed.{| class="wikitable"|+Table 2: Marine HFO Spill Characteristics and Impacts!Category of Marine HFO!Immediate Spill Impact!Environmental Impact!Cleanup Characteristics|Bunker C/Fuel oil No.6|May emulsify, form into tar balls, remain buoyant or sink to the seabed.

Tar-like consistency of HFO sticks to feathers and fur, results in short and long term impacts on marine flora and fauna (benthic, intertidal and shoreline species)|Water recovery of spill is limited, cleanup consists mainly of shoreline and oiled substrate remediation.

|Intermediate Fuel Oil (IFO) 380

Emulsifies up to 3x the original spill volume, may sink to seabed or remain buoyant.	Skimmers are used to recover on-water spill until the oil emulsifies making its removal more difficult. Once coated to the surface, the oil is difficult to remove from substrate and sediment.

|Intermediate Fuel Oil (IFO) 180|Low Sulfur Marine Fuel Oils (HFO derivative)|No ground data to determine immediate spill impact. Laboratory tests suggest behavior similar to other HFO mixtures namely environmental persistence and emulsification.|Limited information. Likely to have similar impacts as IFO with increased initial toxicity due to the higher distillate component causing immediate dispersal and evaporation.|Limited information. Likely to have similar impacts to other HFO mixtures.

History of heavy fuel oil spill incidents since 2000

The following HFO specific spills have occurred since the year 2000. The information is organized according to year, ship name, amount released and the spill location:

• 2011 Golden Traded (205 tons in Skagerrak)
• 2011 Godafoss, Malaysia (200,000 gallons in Hvaler Islands)
• 2009 Full City, Panama (6,300-9,500 gallons in Langesund)
• 2004 Selendang Ayu, Malaysia (336,000 gallons in Unalaska Island - near Arctic)
• 2003 Fu Shan Hai, China (1,680 tons in the Baltic Sea)
• 2002 Prestige oil spill, Spain (17.8 million gallons in Atlantic Ocean)
• 2001 Baltic Carrier, Marshall Islands (2350 tons in the Baltic Sea)
• 2000 Janra, Germany (40 tons in the Sea of Ã…land)NEWS,weblink HFO Project Phase III(a) Heavy Fuel Oil & Other Fuel Releases from Shipping in the Arctic and Near-Arctic, PAME, 2016,

Environmental impacts of heavy fuel oil use

The combustion of HFO in ship engines results in the highest amount of black carbon emissions compared to all other fuels. The choice of marine fuel is the most important determinant of ship engine emission factors for black carbon. The second most important factor in the emission of black carbon is the ship load size, with emission factors of black carbon increasing up to six times given low engine loads.Lack, D. A., & Corbett, J. J. (2012). Black carbon from ships: a review of the effects of ship speed, fuel quality and exhaust gas scrubbing. Atmospheric Chemistry and Physics, 12(9), 3985-4000. Black carbon is the product of incomplete combustion and a component of soot and fine particulate matter (