Petroleum industry hazards

High-profile disasters, such as oil spills or rig explosions, often come to mind in discussions of petroleum industry hazards. More common, yet just as hazardous, are the day-to-day workings of the industry: extracting pressurized, flammable, toxic resources from deep in the earth and then processing and transporting those resources to their final destination. A large part of petroleum extraction and distribution involves dealing with these safety concerns.

Chemistry and Toxicology

Although the word petroleum technically refers only to crude oil, the petroleum industry encompasses the extraction and processing of both crude oil and natural gas. Hydrocarbons—compounds of hydrogen and carbon—are the main components of crude oil and natural gas, and they occur in various states: solid (for example, paraffin), liquid (for example, hexane and benzene), and gas (for example, methane, ethane, and propane). Gaseous hydrocarbons are most familiar in the form of natural gas and liquid hydrocarbons in the form of gasoline.

The hydrocarbons in crude oil are either aromatic (carbon atoms in a ring) or aliphatic (carbon atoms in an open chain). Aromatic hydrocarbons (benzene, toluene, and xylene) have a lower molecular weight, are more difficult to break down in the environment, and are more toxic both in the immediate sense—causing visible sickness—and in the long-term sense because their presence in the air (such as near refineries) is associated with an elevated incidence of cancer and leukemia.

After events such as ocean oil spills hydrocarbons remain in the ocean and are metabolized by organisms at both low and high levels of the food chain; the hydrocarbons remain in their bodies to be consumed by other animals or to be passed to their young. Death, internal organ damage, and reduced ability to swim or maintain body temperature can result. Stationary organisms in intertidal zones are particularly vulnerable, as are juveniles of any species.

In low concentrations, hydrocarbons in the ocean can cause behavioral changes in fish, such as an inability to swim properly. Birds and mammals may lose buoyancy and insulation when oil coats their feathers or fur. By grooming and preening, these animals may ingest the oil, which is harmful to their systems and can affect reproduction and offspring. Toxic hydrocarbons also can sink to the bottom of the ocean and contaminate sediments, which are absorbed by bottom dwellers and detritus feeders.

Petroleum also contains heavy metals, which can pollute the air or water and become a health concern. The majority of environmental pollution associated with the petroleum industry comes not from dramatic, one-time events but from the steady emissions related to automobile use and everyday refinery operations and from runoff on urban roads.

Drilling

Because petroleum reservoirs are below ground, sometimes at great depths, they must be accessed by drilling. Drilling for oil and natural gas on land or offshore is inherently risky because it involves accessing pressurized flammable materials on a large scale and often at distances and depths that are difficult to monitor. In addition, drilling for oil frequently takes place in remote locations, such as the Arctic, where disaster aid is not immediately available.

During drilling, a substance called drilling mud is used to counteract corrosion, lubricate the drill bit, and maintain sufficient pressure to prevent oil and gas from rushing uncontrollably into the well. Drilling mud is made of water, oil, solids like bentonite or barite, chemicals, and sometimes other additives that affect viscosity and weight. If the drilling mud cannot exert sufficient pressure, formation fluids are able to push up against it and enter the well. This is called a kick. When a kick is detected, the composition of the drilling mud is altered to try to counteract the pressure of the reservoir contents. If a kick is not controlled, it can become a blowout (also called a belch), an uncontrolled spewing of oil and gases from the reservoir into the well and out of the well to the surface.

Oil gushers, as blowouts are commonly known, are not a cause for celebration, as they are sometimes shown to be in popular media. Instead, gushers have the potential to cause worker deaths, explosions, fires, and environmental damage. To prepare for the possibility of a blowout, oil wells are equipped with blowout preventers, which can be massive in scale. Their purpose is to clamp down on the wellhead and contain any pressurized contents. When a blowout preventer fails, uncontrolled oil and gas erupt into the ocean or onto the land surrounding the well.

Historically, most drilling has occurred to access oil rather than natural gas, though some natural gas occurs alongside oil. It is cheaper and easier to transport oil, and most natural gas is distributed close to its source for economic reasons. Recently, however, there has been more interest in drilling for gas, particularly with a process called hydraulic fracturing, or fracking, which is used to split rock to access gas. Fracking has been combined with horizontal drilling to create a web of wells that maximize access to pockets of gas. Huge amounts of chemicals are necessary for fracking, and the integrity of the concrete well casings is paramount in preventing water contamination. Fracking is highly controversial because of risks that the extensive rock fracturing will allow toxic substances to reach groundwater supplies.

Transportation of Oil and Gas

Once oil and gas have been extracted from a reservoir, they must be transported to a refinery to be made into usable products. One of the primary methods of transportation is the oil tanker. Tankers can be used to move oil from offshore rigs to onshore refineries or to transport oil from a remote onshore location to a refinery.

The Exxon Valdez was a single-hulled tanker whose 1989 accident and subsequent oil spill led to U.S. legislation to increase tanker safety. The Oil Pollution Act of 1990 required the phasing out of single-hulled tankers and the phasing in of double-hulled tankers for transit within the United States. Double-hulled tankers have an outer hull, an interstitial space for ballast water, then another hull surrounding the tanks of oil. Double-hulled tankers are generally considered safer in terms of their ability to contain oil if the tanker is grounded, but they are less stable because of their higher center of gravity. Countries other than the United States have different specifications for tankers, and some single-hull designs are considered to be as safe as double-hull designs.

Oil is also transported through pipelines. The Trans-Alaska pipeline, for instance, runs above ground, transecting Alaska from Prudhoe Bay to Valdez on Prince William Sound, a distance of roughly 1,300 kilometers (800 miles). Made of steel, the pipeline is vulnerable to corrosion and wear, and like any kind of pipe, it experiences buildup from the contents it transports. A device called a smart pig is periodically run through the pipeline to keep it clear, but even with routine maintenance, pipelines deteriorate and experience breakage.

Pipeline corrosion led to a March 2006, spill of more than 1 million liters (270,000 gallons) of crude oil on Alaska’s North Slope tundra. In the case of the Trans-Alaska pipeline, a winter spill is less harmful than a summer spill because it is more likely to be contained before extensive seepage into the ground or impact to flora and fauna. A spill also occurred in 2010 but of a much smaller magnitude. Making the erosion risk worse, the pipeline was flooded several times between 2019 and 2020 by a nearby river.

In addition to tankers and pipelines, oil is transported via trucks and trains. According to information from the US Department of Transportation’s Pipeline and Hazardous Materials Safety Administration, crude oil spilled during US rail incidents spiked in 2013, with 1.5 million gallons of crude oil spilled that year, compared to a total of 800,000 gallons spilled between 1975 and 2012. That same year, an unmanned train carrying oil exploded in Lac-Megantic, Quebec, killing forty-seven people and spilling 1.5 million gallons of crude oil in a single day. The accident increased the intensity of the debate over the safest oil transportation method. By 2020, around 1.02 million barrels were being transported via rail every day. On average, one thousand crude oil train spills were occurring annually.

Oil Spills

Oil spills can occur on land or offshore. On land, a priority is to prevent the spill from entering any water systems, above or below ground, and to keep the spill from reaching areas of human habitation. A localized spill may occur at an oil well or may occur during transit.

Pipeline spills result from corrosion of the pipe or from damage by vandals. An illegal tap of a Mexican pipeline in 2010 triggered an explosion that killed twenty-eight people and caused extensive spillage. An Exxon pipeline ruptured in 2011, pouring oil into the Yellowstone River in Montana. In 2013, a Tesoro Corp. pipeline break caused 840,000 gallons of oil to be spilled in North Dakota, which took nearly four years to clean up. Slightly smaller than the 2013 spill, the Keystone Pipeline spill of 2022 leaked 588,00 gallons of oil into the waterways of Kansas. In July 2024, heavy rain from a typhoon led to the sinking of an oil tanker, MT Terra Nova, in Manila Bay in the Phillippines. The tanker was carrying 1.4 million liters of oil. Phillippine's Coast Guard and other agencies worked to contain the oil.

The oil spills most often noted by popular media occur offshore from well blowouts or accidents during transit by tanker. After a spill in the ocean, a number of natural processes affect the oil. The more volatile compounds in the petroleum will evaporate into the air. The water will disperse the oil instead of mixing with it because oil is lighter than water. Seawater in particular is even less likely to dissolve oil than is freshwater. Sunlight, to some extent, will break down the oil, making it slightly more soluble. Microorganisms also will begin to oxidize the oil.

Cleanup efforts can be mechanical or chemical. Mechanical cleanup includes the use of booms and skimmers. Booms are generally made of plastic or metal, and they serve as simple barriers to the spread of the oil slick. Skimmers are boats that travel along the slick and physically skim the oil from the water. It also is possible to instigate a controlled in situ burn to remove some of the surface oil.

Chemical dispersants can be applied to break up the oil into droplets that will sink instead of remain on the surface of the water. This reduces the chances that the oil will reach sensitive coastal areas, but the toxicity of dispersants makes them controversial because large quantities are required for treatment. Because of their toxicity to marine life, oil spill cleanups must address cleaning both animals and their habitat, including beaches and intertidal rocks. This involves steam cleaning and other painstaking procedures.

The Exxon Valdez and Deepwater Horizon Disasters

The Exxon Valdez was a giant oil tanker that ran aground at Bligh Reef in Prince William Sound, Alaska, in 1989, puncturing its single hull. A combination of factors, including the remote location and poorly organized response efforts, led to the spilling of approximately 42 million liters (11 million gallons) of oil into the water. It was the largest spill in US history at the time.

A number of cleanup methods were employed to mitigate the effects of the spill. These included burning the oil, using booms and skimmers, and applying chemical dispersants. Both the burn and the dispersants were less effective than they might have been because of poor weather and water conditions. As a result, the oil coated much of the shoreline, affecting birds and seals. Whales, porpoises, and other species were affected in less immediately visible ways.

The Deepwater Horizon explosion in April 2010, in the Gulf of Mexico made the Exxon Valdez spill seem mild in comparison. Deepwater Horizon was a semisubmersible oil rig capable of drilling a well deeper than 10,668 meters (35,000 feet), a depth greater than the height of Mount Everest. The bottom of the well was 5,596 m (18,360 ft, or 3.48 mi) below sea level, and it was under tremendous pressure.

The first sign that something was wrong came when the crew experienced lost returns: The amount of drilling fluid they were sending down was not coming back up again, a situation that indicated leaks in the well walls. The well then began to kick, a warning sign of a potential blowout.

Other signs of trouble existed, including high pressure readings and more return fluids. Hydrocarbons were making their way past the blowout preventer (BOP) and into the well. The crew finally tried to activate the BOP, but the BOP was unable to do its job. Highly flammable and explosive gases and liquids surged from the well and the rig caught fire and exploded, killing eleven people and injuring sixteen more.

Five million barrels of oil spilled into the Gulf of Mexico. As with previous spills, dispersants and physical containment measures (booms) were implemented. The flow was finally halted, albeit temporarily, with a capping stack (a type of seal). The stack placement was followed with a static kill, the insertion of heavy drilling mud and subsequent cementing of the well. Later, a relief well was completed, and the reservoir was fully sealed. Investigators failed to find any one cause of the disaster. Though the failure of the BOP was the most immediate reason for the blowout, many other events led to that outcome.

The Local Petroleum Industry

Much oil and gas exploration and extraction takes place in remote locations. Occasionally, what is normally out of sight is brought to the public’s attention.

Public concerns over extensive hydraulic fracturing arise because the process might affect drinking water. Oil spills make headlines because they affect coasts and beaches, bringing crude oil in contact with humans and animals. The Deepwater Horizon explosion had a huge impact on marine life and ecosystems in the Gulf of Mexico and, by extension, on the economy of the Gulf states, which rely heavily on tourism and seafood industries.

Refining is one petroleum industry process that often takes place near population centers. In refining, crude oil is heated and different products (called cuts) are drawn off based upon their boiling points. Gasoline is one of the first products to separate, while heavier products require higher temperatures for extraction. In addition to gasoline, kerosene, diesel, and heavier oils and paraffin are produced. A refinery unit called a cracker can take heavier cuts and break them down to extract gasoline, for which there is more demand.

Petroleum processing entails high temperatures and the use of dangerous chemicals. A number of things can go wrong during refining. The cracking units process thousands of barrels of oil each day and shutting down the units severely curtails productivity. In 2010, an estimated 7,711 kilograms (17,000 pounds) of benzene spewed into the air of Texas City, Texas, sickening residents. (The hydrogen compressor of the refinery’s ultracracker unit had failed, but the refinery continued to process.) Other refinery pollutants include hexane, butane, heptane, pentane, and propylene, which affect the respiratory system and the central nervous system in various ways when they are present in large quantities.

Refinery accidents can be more dramatic than clouds of pollution. The volatile chemicals employed during distillation require careful handling and processing. Small-scale explosions of pressurized pipes can injure or kill workers, but large-scale explosions also occur. For instance, at an isomerization unit (which alters the molecular structure of hydrocarbons to form products such as gasoline additives) at one refinery in the United States, incorrect pressure readings, alarm failure, and the inability of the blowdown drum to vent a sudden rush of gases contributed to an explosion that killed fifteen workers. Flaring equipment and a more effective venting system might have averted the disaster, but keeping refineries updated and in safe working condition is expensive.

Principal Terms

aromatic hydrocarbons: a toxic hydrocarbon group that includes benzene, toluene, and xylene

benzene: a carcinogenic aromatic hydrocarbon found in crude oil; an important ingredient in gasoline

blowout preventer: a massive device used at a rig wellhead to function as a shutoff valve if the pressure in a reservoir gets out of control

boom: a metal or plastic barrier used to prevent the spread of oil during a spill

dispersant: a chemical that breaks spilled oil into droplets that will sink instead of remain on the surface of the water

fracking: hydraulic fracturing; uses water and chemicals to break up shale and release natural gas

hydrocarbons: compounds of hydrogen and carbon; the main component of petroleum and natural gas

kick: a “belch” during uncontrolled pressure in a reservoir; can lead to a blowout or a gusher

methane: the main component of natural gas

skimmer: a vessel used to skim oil from the surface of water after an oil spill

Bibliography

Conca, James. “Pick Your Poison for Crude—Pipeline, Rail, Truck or Boat.” Forbes, 26 Apr. 2014, www.forbes.com/sites/jamesconca/2014/04/26/pick-your-poison-for-crude-pipeline-rail-truck-or-boat. Accessed 26 July 2024.

Fischetti, Mark. “The Human Cost of Energy.” Scientific American, vol. 305, no. 3, 2011, p. 96. www.scientificamerican.com/article/the-human-cost-of-energy. Accessed 26 July 2024.

Lerner, Steve. Sacrifice Zones: The Front Lines of Toxic Chemical Exposure in the United States. MIT Press, 2012.

Magner, Mike. Poisoned Legacy: The Human Cost of BP’s Rise to Power. St. Martin’s Press, 2011.

Mehta, Saima. "Ship Carrying 1.4 Million Litres of Oil Sinks Near Philippines: How Oil Spills Impact the Environment." The Indian Express, 25 July 2024, indianexpress.com/article/explained/explained-sci-tech/oil-spill-philippines-impact-9477308/. Accessed 26 July 2024.

Mooney, Chris. “The Truth About Fracking.” Scientific American, vol. 305, no. 5, 2011, pp. 80–85. www.scientificamerican.com/article/the-truth-about-fracking. Accessed 26 July 2024.

National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling. Deep Water: The Gulf Oil Disaster and the Future of Offshore Drilling. Author, 2011.

"Oil and Gas Extraction." Occupational Safety & Health Administration, www.osha.gov/oil-and-gas-extraction/hazards. Accessed 26 July 2024.

U.S. Forest Service. Final Environmental Impact Statement: Changes Proposed to Existing Yellowstone Pipeline Between Thompson Falls and Kingston. Author, 2000.