When a hazardous substance release or oil spill is reported, environmental authorities may perform a variety of emergency response actions. This is done through emergency response facilities and regional offices in close cooperation with a network of federal, state, and local governments. When a hazardous substance release is reported, emergency response programmes set their procedures into motion . Many steps and safety precautions must be followed to ensure a swift and effective response to the emergency.
Site investigation is the initial step in any responsive action. Responders may not have all the relevant information when a release is first reported, such as how the issue occurred, the extent of the harm, or even what hazardous compounds are involved. Site assessment also enables responders to evaluate the best reaction options and safety precautions to take during the response operation.
Once the information has been gathered about the event, responders will consider the hazardous substance’s health and ecological risks and possible exposure pathways. They may use response methods including:
Using chemicals to stop the spread of the hazardous substance release;
Removing hazardous substances in soil or containers;
Encasing hazardous substances in place or otherwise ensuring that winds or rain do not move them around;
Providing a safe supply of drinking water to people affected by hazardous substance contamination;
Draining waste ponds or repairing leaky waste disposal pits so that hazardous substances do not seep into the ground;
Installing fences to prevent direct contact with hazardous substances.
Burning or otherwise treating hazardous substances; and/or
Temporarily moving residents affected by hazardous substance contamination while cleanup activities take place
1.2 Site Investigation
Oil spills will continue to occur as long as our societies depend on petroleum and its products. This is due to the inherent potential for human error and equipment failure in producing, transporting, and storing petroleum. Although it is essential to focus on preventing oil spills, methods for controlling them and cleaning them up must also be developed.
Commonly, an established set of procedures is followed to investigate the site, estimate the threat, and determine the best course of action. The US Environmental Protection Agency (EPA), for instance, designates an On-Scene Coordinator to appraise the incident and select the most suitable response intervention. If the coordinator concludes that EPA will take the lead in responding to the incident, they will evaluate the urgency of the situation to define the appropriate response alternative.
Traditional identification and investigation methods for fuel spills can be expensive, hazardous, and time-consuming, commonly taking days to prepare and begin cleanup efforts. Aerial panchromatic photography struggles at discriminating petroleum from water, especially in terrestrial conditions. Hyperspectral imaging is now becoming more common for quick and reasonably accurate identification and quantification of contaminated soils and more broadly in other environments.
The ability to monitor fuel spills using remote sensing technology has the potential to enable informed decisions to be made by first responders, environmental consultants, petroleum companies and governmental agencies. This would result in better responses and lesser ecological and human health impacts. Such an approach is advantageous because direct, ground monitoring of fuel spills is hazardous due to potential combustion and explosion hazards. A full spatial view of the event is often not possible from the ground.
1.3 Introduction to Contingency Planning and Response Initiation
An integrated system of contingency plans and response options can speed up and improve the response to an oil spill and significantly reduce the environmental impact and severity of the spill. The purpose of contingency plans is to coordinate all aspects of the response to an oil spill, including stopping the flow of oil, containing the oil, and cleaning it up. The scope covered by contingency plans could range from a single bulk oil terminal to an entire section of coastline. Like forest fires and other environmental emergencies, oil spills are not predictable and can occur anytime and during any weather. Therefore, the key to an effective response to an oil spill is to be prepared for the unexpected and to plan spill countermeasures that can be applied under even the worst possible conditions.
Oil spills vary in size and impact and require different levels of response. Contingency plans can be developed for a particular facility, such as a bulk storage terminal, which would include organisations and resources from the immediate area, with escalating plans for spills of greater impact. Contingency plans for provinces, states, or even an entire country usually focus more on roles and responsibilities and provide the basis for cooperation between the appropriate response organisations rather than specific response actions.
Most contingency plans typically include the following:
A list of persons and agencies to be notified immediately after a spill occurs
An organisation chart of response personnel and a list of their responsibilities, as well as a list of actions to be taken by them in the first few hours after the incident
Area-specific action plans
A communications network to ensure response efforts are coordinated among the response team
Protection priorities for the affected areas
Operational procedures for controlling and cleaning up the spill l Reference material such as databases, GIS systems, sensitivity maps, and other technical data about the area
Procedures for informing the public and keeping records
An inventory or database of the type and location of available equipment, supplies, and other resources
Scenarios for typical spills and decision trees for certain types of response actions such as using chemical treating agents or in-situ burning
Response options detailed in contingency plans must be tested frequently to remain effective. This testing is conducted by responding to a practice spill as though it were real. This varies from tabletop exercises to large-scale field exercises in which equipment is deployed, and oil is theoretically “spilt” and recovered. Such activities not only maintain and increase the skills of the response personnel but also lead to improvements and fine-tuning of the plan as weaknesses and gaps are identified.
2 OIL SPILL RESPONSE TECHNIQUES
2.1 Mechanical Containment or Recovery
One of the primary and effective methods of responding to oil spills is through mechanical recovery. It is, in fact, one of the methods primarily used by governments around the world for cleaning up oil spills on different scales due to the various available designs dealing with varying scales of operation, environmental conditions and oil types.
Damage to spill-contaminated shorelines and dangers to other exposed sites can be lessened by timely and proper use of containment and recovery equipment . In most cases, mechanical containment or recovery is the first line of defence against oil spills. Mechanical containment is used to capture and store the spilt oil until it can be disposed of properly. The equipment to contain and recover spills includes a variety of floating booms, barriers, and skimmers, as well as natural and synthetic sorbent materials.
Booms are floating, physical barriers to oil, made of metals, plastic, or other materials . Containment booms are used to prevent oil spread from polluting shorelines and other ecosystem resources. Booms also help concentrate oil in thicker surface layers, turning recovery procedures easier. In addition, they may be used to divert and channel oil slicks along preferred paths, making them simpler to remove from water surface. Despite the fact that booms are designed and constructed in a variety of ways, they all have the same four basic parts:
An above-water “freeboard” to contain the oil and keep it from splashing over the top of the boom due to waves
A flotation device
A below-water “skirt” to confine the oil and help reduce the amount lost under the boom
A “longitudinal support,” ordinarily a chain or cable running beneath the skirt that strengthens the boom against wind and waves action; it may also serve as a weight or ballast to add stability and help keep the whole boom upright
Booms can be divided into some basic types.
Fence booms have a high freeboard and a flat flotation device, yielding them ineffective in open waters where the boom might twist due to wave and wind action.
Curtain booms have a more circular flotation device and an unbroken skirt. They perform well in rough water but are more difficult to clean and store than fence equivalents.
Inflatable, non-rigid booms come in many shapes. They are easy to clean and store and withstand rough seas environments. They are, however, more expensive and more challenging to operate and puncture and deflate quickly.
Water conditions significantly impact all boom types; the more the waves surge, the less effective booms become. Booms can be anchored to a structure, such as a buoy or a pier, or towed behind or alongside one or more vessels. When stationary, the boom is moored below the water surface. Stationary booms must be watched due to changes produced by winds, shifting tides, tidal currents, or other factors that modify water depth, direction, and force of motion. These forces may significantly hinder the ability of a boom to hold oil. Most booms perform well in mild waters with smooth, long waves. In general, booms will not operate properly when waves are higher than one meter, or currents hit speeds of one knot per hour or faster.
Fortunately, booms can be improvised from whatever materials are available when a spill happens, and no containment equipment is available — these are made from such common materials as inflated fire hoses, wood, plastic pipe, empty oil drums, and automobile tires. They can be as basic as a board laid over the surface of a slow-moving stream or a berm constructed by bulldozers pushing a wall of sand out from the beach to redirect oil away from a vulnerable area of shoreline. Sometimes, two boats will tow a collection boom, allowing oil to concentrate within it, where a skimmer then picks it up.
A skimmer is a device for retrieving spilt oil from the water’s surface — they may be self-propelled, used from shore, or operated from vessels. In other words, skimmers are boats and other devices that can remove oil from the sea surface before it reaches sensitive areas along a coastline. Sometimes, oil is being skimmed from the sea surface by a “vessel of opportunity.”
The efficiency of skimmers is very much dependent upon conditions at sea. Skimmers tend to recover more water than oil in moderately turbulent or choppy water. Depending on the type of oil being recuperated, the presence of ice or debris in the water, and the sea conditions during cleanup activities, different kinds of skimmers offer benefits and drawbacks.
Figure 2. A “vessel of opportunity” skims oil spilt after the 2010 Deepwater Horizon/BP well blowout in the Gulf of Mexico. Source: https://www.noaa.gov/
Oleophilic skimmers relatively have the highest recovery efficiency. They are most effective with medium viscosity oils but not as effective with less viscous oil products such as kerosene or diesel
Oleophilic skimmers use materials that adhere to the oil as they rotate, then the oil is scraped off and allowed to be dropped into a sump from where it is pumped for storage.
One of the most straightforward designs to separate oils from water involves a suction device that physically pumps or suctions out the oil from the water surface. These skimmers are widely available through vacuum trucks and trailers. The challenge with this device is that storage of recovered oil is limited. Placing a hose attached to a vacuum pump without a weir skimmer increases entrained water; relatively high proportions of water is also consequently collected, and it should then be decanted to maximise available oil storage potential.
The concept of weir skimmers is that it uses gravity to separate and trickle oil from the water surface selectively. In most cases, weir skimmers are attached to oil suction/vacuum devices or machinery such as the truck suction skimmers with the weir option mentioned earlier. The biggest challenge of using weir skimmers is its decreased efficiency in wavy conditions; however, many designs are now available in the market with improved efficiency. Some examples of weir skimmers include adding a belt adaptor to enhance the capability of the base weir skimmer in highly viscous oils and improvised options of weir skimmers through using plastic bottles and metal offcuts. A traditional weir skimmer is best used in calm waters.
Other types of skimmers are also available, and they are adapted to improved efficiency, especially in wavy seas with rougher conditions. Upward rotating belts using oleophilic materials can be used by partially lowering them beneath the water to reduce the hindrance caused by the waves. Some designs also involve the use of buckets or paddles on the belt itself to help with the physical separation of the oil from the water .
Dispersing and gelling agents are most suitable for keeping oil away from reaching shorelines and other sensitive habitats. These can be used in conjunction with mechanical techniques for containing and cleaning up oil spills. Biological agents have the potential to assist recovery in sensitive areas such as coastlines, marshes, and wetlands. Contingency plans establish the process for authorising dispersants and other chemical response agents. Some also include the ‘product schedule’, the official listing of chemical countermeasures at hand during or after an oil spill response.
Dispersants are chemicals that separate the oil into the water column so that much less stays at the surface, where it could affect beaches and tide flats. Using aircraft or boats to apply these is a viable method, yet, only effective when conditions are conducive to using them.
When used judiciously and in the right circumstances, applying chemical dispersants can effectively accelerate the dispersion of oil from the sea surface into the water column. This, in turn, helps to accelerate dilution and biodegradation of the oil and reduce the environmental and economic impact of spilt oil. However, prior to the use of dispersants, consideration must be given to the impact of the dispersed oil on sub-surface resources, such as fish stocks and coral.
Within the European Union, an inventory of national practices and policies relating to the use of dispersants as an oil spill response tool, which was undertaken by the European Maritime Safety Agency (EMSA), has revealed a divergence of opinion amongst EU Member States . In most states, dispersants are secondary to mechanical containment and recovery. In several states, dispersants are either not allowed or are highly restricted, particularly in the Baltic States. In other countries where dispersant use is permitted, in practice, they have not been used for a decade or more.
The above chart compares the types of oil involved in the spills attended by ITOPF  between 1995 and 2005 and shows that a large proportion (39%) of the spills treated with dispersant were spills of heavy fuel oil (IFO 380 and above). This is despite the general acceptance by oil spill response specialists that dispersants are less effective on heavier oils. Past studies, trials and observations from actual spills have shown time, and again that weathered heavy fuel oils are often too viscous for dispersants to penetrate and be effective. Nevertheless, they have been used significantly on such oils over the past ten years. In certain scenarios, such as when the fuel oil is fresh, and the sea temperature is high, dispersants may be effective, particularly if the country involved has a policy to use dispersants and arrangements are in place to respond quickly. In many cases, however, it is simply the political need to be seen doing something that drives dispersant use on oil spills irrespective of the circumstances.
Also known as solidifiers, gelling agents are chemicals that react with oil to form rubber-like solids. In case of rather minor spills, these chemicals can be applied by hand and left to blend and fuse on their own. For treating larger disasters, the chemicals are applied directly to the contaminant, then mixed in by the force of high-pressure water streams. The gelled oil is removed from water using suction equipment, nets, or skimmers, and is sometimes reused after being mixed with fuel oil.
Gelling agents can be used in serene to moderately rough seas since the mixing energy provided by waves exaggerates the contact between the chemicals and the oil, resulting in more significant solidification. There is one drawback to using solidifiers — large quantities of the material must often be applied, as much as three times the volume of the spill. For events comprising millions of gallons, it is impractical to store, move, and apply such large quantities of material .
Biodegradation is a process by which microscopic organisms such as bacteria, fungi, and yeast break down complex compounds into simpler products. Biological agents are biochemicals or organisms that increase the rate at which natural biodegradation occurs. Biodegradation of oil is a natural process that slowly gets rid of oil from the aquatic environment. However, rapid removal of spilt oil from shorelines and wetlands is needed in order to minimise potential environmental damage to these sensitive habitats .
Bioremediation refers to the act of adding materials to the environment, such as fertilisers or microorganisms, that will increase the rate at which natural biodegradation occurs — this technology can help treatment processes work faster. Two bioremediation technologies that are currently being used around the globe for oil spill cleanups are:
Fertilisation– the method of adding nutrients such as phosphorus (P) and nitrogen (N) to a polluted medium to stimulate the growth of the microorganisms capable of biodegradation; and
Seeding – the addition of microorganisms to the current native oil-degrading population. As with fertilisation, the purpose of seeding is to increase the number of microorganisms that can biodegrade the spilt oil.
2.3 Physical Methods
Natural processes can start the shoreline cleanup process but are generally too slow to provide adequate environmental recovery—for instance, evaporation, oxidation, and biodegradation. Physical methods such as wiping with sorbent materials, pressure washing, and raking and bulldozing can be used to assist natural processes .
Materials capable of absorbing their weight and more in oil can be used to wipe up petroleum from contaminated shorelines. These materials are often conceived as large squares, much like paper towels, or shaped into “mops.” The squares or sweepers are used to wipe the shoreline or oily stones, during which time the absorbents are filled with as much hydrocarbon as they can bear. Among the advantages of using absorbents, it is worth mentioning that they can be employed to clean up any kind of oil on any coastal site reachable by response personnel. Absorbents are generally inoffensive to the shoreline itself or to domestic organisms, and no material is left behind following the cleanup effort. Given that some sorbents are reusable, the need for disposal after a spill can be reduced.
Wiping with absorbent materials requires several personnel individuals and a large quantity of material. Personnel must wear ad hoc protective clothing to minimise direct contact with the oil while removing it. Oil-filled absorbents and protective clothing used by response personnel must be appropriately disposed of following cleanup, which can be costly. In addition, the intrusion of many people onto an isolated shoreline may disrupt animal behaviours such as breeding or nesting.
Pressure washing means rinsing oiled shorelines and rocks using hoses that deliver low- or high-pressure water streams, which, in turn, can be hot or cold. The oil is flushed from the sands into plastic-lined trenches, then amassed with sorbent materials and disposed of accordingly. Since some river banks and lakes have vegetation reaching into them or growing literally in the water, plants may have to be brushed or removed.
Low-pressure washing can usually remove the majority of oil off vegetation, depending on the type of oil. High-pressure washing causes more harm than good in a coastal habitat by forcing oil deeper into the beach and killing many marine organisms. Besides, high-pressure water streams can precipitate bank erosion and displace organisms, such as mussels and algae, from the rocks and sediments they occupy or can force oil deeper into debris, making cleanup more difficult.
Pressure washing has the advantage of being relatively inexpensive and straightforward to apply; however, it requires numerous staff.
Raking or Bulldozing
Contamination becomes more difficult to remove when oil moves downward into the sands or between pebbles and cobbles on a shoreline. Tilling or raking the sand can increase evaporation only if the oil has moved downward only a short distance — this is achieved by increasing its exposure to air and sunlight. Otherwise, if the oil has penetrated several inches into the soil, responders may bring bulldozers in to remove the upper layers of sand and pebbles. This measure allows the oil to be uncovered so it can be collected and removed from the site, washed with pressure hoses, or left to evolve naturally.
Raking and bulldozing are simple techniques for helping to remove oil that might run into sediments. However, these methods can upset the plant and animal species that live on and in the sediments, as well as the natural shape of the shoreline. In addition, the use of bulldozers requires specially trained operators who can manoeuvre them without damaging other nature elements unnecessarily; raking and tilling are time-consuming and demand many people.
2.4 In-situ burning
If local authorities and response experts agree, other possible—but contentious—measures managers might consider including some alternative procedures.
In-situ burning (ISB) of an oil slick before it reaches the coast. To do this, responders cage some of the oil from the slick in a fire-proof boom, then ignite it. This technique works best when the spill is fresh and the weather is relatively calm. In-situ burning involves the controlled incineration of oil that has leaked from a vessel or a facility, at the location of the spill. When conducted properly, it significantly reduces the amount of oil on the water and minimises the adverse effect on the environment.
Fundamentally speaking, ISB involves the removal of oil by burning the spilt oil on the sea surface. It offers the potential to rapidly convert released oil into combustion products while allowing a small percentage of unburned oil and burn residue to remain on the surface, within the water column, or sink to the seafloor. In several experimental and field tests, ISB has been shown to have >95% removal (or burn) efficiency by mass for hydrocarbon removal.
Compared to other response options, burning of the oil in an offshore environment requires fewer logistical personnel and less equipment and reduces the chance for shoreline contamination and oiled terrestrial, aquatic and avian resources. The three basic ISB requirements are fuel, oxygen, and a source of ignition. It is also advisable that the oil spill be low in water content (preferably <20–30% water), with a minimum slick thickness of 2–3 mm and be a sufficient and safe distance from people and property. Thinner oil layers lose heat to the underlying water and therefore cannot sustain vaporisation of the flammable components from the oil. At these optimum conditions, ISB can remove an estimated 600–1800 barrels (100–300 tons) of oil per hour . In-situ burning as an oil spill response technique requires oil containment, ignition, control and was first used in the Arctic in 1958 in response to the Mackenzie River pipeline spill . A series of Arctic field experiments were performed in the 1970s and 80s, followed by a recent resurgence in studies conducted in the early 2000s. These studies are mainly responsible for in-situ burning becoming accepted as having the highest probability of success as an oil response strategy in situations involving spills in ice-covered waters. One area which can be addressed operationally is oil slick thickness. Oil slicks have traditionally been increased using fire booms to corral and contain the oil to enable sufficient thickness for burning. Within the Arctic, loss of oil slick thickness can be decreased naturally as a result of reduced water temperature and natural confinement by ice floes. At ice coverage of >70%, booms would not be needed as natural confinement of the oil would occur; additionally, under 30% ice cover, most open water response technologies are feasible. For incidents when the slick thickness is insufficient to conduct an ISB, chemical herders may be an option to induce greater thickness and oil containment. While chemical herder application has not yet been used in actual spill response, it has been tested in multiple Arctic conditions.
2.5 Wildlife Protection
Terrestrial ecological components are prone to multiple impacts that occur due to oil spills. In general, these include loss of productivity of the ecosystem, reduction in species composition, mortality of fauna as a result of being trapped in oil lakes, potential mortality due to accumulation of toxins, and changes in behavioural patterns due to changes in the surrounding environment. Scare methods are employed to keep birds and animals away from oil spill regions. Devices such as propane scare cannons, floating dummies, and helium balloons are often used, for the most part, to keep away birds.
Marine habitats and species show varying responses to oil spills. Fish are negatively affected, given that there is a possibility of directly ingesting oil through gills. This leads to biological responses such as reduced growth, changes in metabolic rates, and a decline in reproductive success. Eggs and larvae are also negatively affected by spills. Evidence of marine vegetation deterioration varies. Some species exhibit die-offs, while others, such as algae and mangroves usually regenerate pretty rapidly depending on existing conditions . Similar to the effects on soil and groundwater, it is documented that oil spills also negatively affect marine water quality and sediment quality by increasing the concentrations of hydrocarbons and secondary pollutants.
Oil that washes up on beaches has lost most of its toxicity. However, there were still many detrimental effects observed due to the slicks’ physical properties. The vast oil slicks that form near the shoreline damage vegetation along the shore due to temperature increases that formed as a result of the black coloured surface’s increased heat absorption. Oil slicks impact marine vegetation by blocking light, thereby impeding effective air exchange. Oil slicks in some areas also harden into tar and seep into the subsurface, destroying several species and benthic habitats.
Figure 6. A fish swims under oil slicks in Huntington Beach, California, 2021. Credit: REUTERS/Gene Blevins.
3 ACTIVATION OF CONTINGENCY PLANS
The response actions expressed in contingency plans, whether for spills at a single oil and gas facility or in an entire region, are divided into the following phases: alerting and reporting, assessment and mobilisation, containment and recovery, clearance, and remediation or restoration. Pragmatically, these phases often co-occur rather than follow each other sequentially. Most contingency measures also allow for a ‘tiered reaction’, which means that response steps and procedures escalate as the incident becomes more severe.
As the gravity of an incident is often unknown in the initial phases, one of the priorities is determining the magnitude and potential impact of the spill. The first step in activating an oil spill contingency plan is to notify first responders and the responsible government agency. Leaving aside the size or seriousness of the spill, reporting a spill to the designated agency is legal enforcement in most jurisdictions.
The emergency response staff assess the situation and take action as soon as possible to control, contain, or reduce environmental damage. Employees carry out their roles in accordance with the contingency plan and training until the whole command structure is in place and operational. This underlines the significance of a precise contingency plan for this phase of the operation, as well as a high level of first-responder training.
Stopping the flow of oil is a major priority in the first phase of the operation; even the response may need to be quick and done in tandem with the flow stoppage. In the case of a marine accident such as a ship grounding, halting oil flow may not be possible. However, the spillage may be attenuated by pumping oil in the ruptured tanks into intact ones or pumping oil from leaking spots into other tanks or barges. These operations may take up to a week to complete and are often delayed by bad weather. During this time, emphasis has still been on containing the oil or diverting it from sensitive areas.
As oil spills pose many dangers, safety is a major concern during the early phases of the response action:
The physical environment at the site may not be well known
Most petroleum derivates are flammable or contain volatile and combustive compounds, creating a serious explosion and fire danger in the early phases of the incident.
Spills may materialise during bad weather or darkness, which increases the danger to the response crew.
The response plan begins to take shape as more of the people who were notified arrive on the scene and begin to perform their roles. Response strategies vary from episode to episode and in particular circumstances and take varying amounts of time to carry out. Action after a minor spill may be fully operational within hours. In contrast, for a more significant spill, response elements such as shoreline assessment after cleanup may not take place until weeks after the incident.
Fuel spills are a widespread occurrence globally . These events are associated with the regular operation of petroleum product systems and with accidents such as extreme weather, storage leaks, vehicular collisions, mechanical failure, and general accidents in transporting and extraction. Spills occur at a variety of scales and types.
Selection of oil spill response methods should be based on: oil type, nature and location of the spill, the environmental conditions, and the availability of personnel and equipment. The spill response goals are to prevent as much oil as possible from moving into the nearshore and shoreline areas and reduce the oil’s volume and toxicity in the offshore environment. Differences in proximity to communities and infrastructure, risk, geography, climate and scale of challenge make an evaluation of response capacity and the design of solutions difficult.
The spill response toolbox requires flexibility to evaluate the community’s needs and the environment and apply multiple response options as appropriate. Traditional oil spill response options include mechanical recovery; chemical dispersants; in-situ burning; subsea containment; surface containment; natural dispersion; evaporation; photo-degradation; shoreline cleanup; biodegradation; and monitoring & surveillance.
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