The issues about dispersant use, originated with the Torrey Canyon incident in 1967 off the Scilly isles in south west England. This was the first major tanker incident spilling approximately 120,000 tonnes of crude oil. (full story in Major spills section)
She ran onto rocks then during the salvage attempt there was an explosion in the engine room killing 2 men. The British government decided to try and burn the cargo using napalm bombs which successfully broke the ship apart allowing the oil to escape and contaminate both England and France.
The use of massive quantities degreasers and detergents which were effective at dispersing the oil but due to their highly aromatic and toxic content they caused disastrous effects on marine life lasted for more than a decade. These effects were compounded by the lack of suitable application equipment, with a result that high local concentrations of chemicals developed especially in shallow waters
Since 1967 many improvements have been made:
From a product point of view
From the application point of view
As a result it is now possible to apply low toxicity dispersants in a rapid and effective manner either from the air or sea.
But the Torrey Canyon issue still arises every time dispersant spraying operations start usually from Greenpeace.
Before any dispersant is used there is a need to read and understand the countries regulations, these will state minimum water depths, distance from the coast and current necessary for their use as well as where to gain permission for their use. The countries that signed the International Convention on Oil Pollution Preparedness, Response and Cooperation (OPRC 90), are required to establish a National Response System for response to oil pollution incidents. This includes the regulation for the use of chemical dispersants or not.
It is important to employ a mathematical model for the drift of oil slicks to predict the movement of the oil slicks on the sea.
These photographs show the difference between natural dispersion and dispersant dispersion. The droplets can be clearly seen on the left and have the ability to re-coelese and rise to the surface again.
The chemically dispersion on the right shows the droplets the size of dust particals and as such do not have the ability to rise again and so drift away with the current which in most countries that allow the use of chemical dispersants is a minimum of 1.5 knots.
Photos Delft Hydraulics Institute
The largest case of natural dispersion
Photo BBC I took this photo in May 1994
The MT BRAER oil spill at Fitfull head, Shetland Isles,
A combination of the light Norwegian Gullfaks oil, southerly gale with wind speed up to 240kph and enormous wave energy naturally dispersed the oil into the water column.
The oil droplets adhered to sediment particles which then sank to the sea bed. This oil spread over a very wide area due mainly to sub-surface currents.
It has been said that the amount of PAH's present in the water column were much less that would have been the case if only chemical dispersant had been used.
What are chemical dispersants?
They are made up of active ingredients, called solvents and surfactants, the solvent molecule of which is composed of an organic carbon chains, basically has an affinity for oils and greases (oleophilic) while the surfactant has an affinity for water (hydrophilic).
These two components working together when spayed onto oil that is amenable to dispersant (to light and the dispersant will pass though into the water, to viscose and the solvent will not be able to enter the oil) it works its way through the oil to the oil water interface.
Here it reduces the surface tension between the oil and the water literally pulling the oil apart therefore aiding the oil to be dispersed into minute droplets (simular to the size of dust) in the water column they remain in suspension below the surface, so small they do not have the ability to resurface and re-coalese into a slick.
This accelerates the natural process of degradation and dispersion, thus assisting the biodegradation of the oil in the environment.
Chemical dispersants are used during oil spills, for the purpose of protecting natural and sensitive socio-economic resources such as coastal and marine ecosystems. Their applicability, however, should be carefully established.
It should only be accepted if it results in net environmental benifit, when compared to the effects caused by a spill with no treatment or employed as an alternative and/or additional option for the containment and removal of the oil.
The efficiency of the dispersants, among other factors, is related to the degree of weathering of the oil at sea, weathered oils become more viscous and may also undergo emulsification, factors that reduce the efficiency of these chemical agents.
Therefore, the application of the chemical dispersants usually takes place within the first 12 hours following the spill. This is the window of maximum opportunity. The majority of products presently available have a reduced effect if applied after the weathering process of the oil has already begun or the formation of viscous emulsions (mousse).
With emulsified or highly weathered oils the dispersant cannot penatrate to the oil water interface and so stays on top of the oil. With wave action it can be deposited into the sea turning the water milky Photo right this was taken during the Torry Canyon spill in 1967. Milky water is a good indication that the dispersant is not working on the oil or has been applied to the water and not the oil.
As I said at the top of the page, these were nothing like the dispersant we use today they were degreases and detergents as at this time there was nothing else. They did a huge amount of damage.
Dispersants have change dramatically over the years but from the photographs below unfortunately they are used on the wrong types of oil in what can only be decribed as "being seen to be doing something" this usually gains huge criticism and quite rightly from green organisations about "chemicals being added to an already polluted sea" and then the press jump on the band wagon.
Photo left is during the Montara blow out in the Timor Sea in 2009 showing dispersant being sprayed on orange emulsified crude oil which is a waste of time and money.
Photo right showing dispersant being sprayed on more emulsified oil in 2010, during Deepwater Horizon.
The link below shows the USAF spraying clear water and emulsion both a waste of time and money. The aircraft filming this should have been putting the spray plane on target and telling him when to start and stop spraying. It looks more like a pleasure flight than anything else. http://www.youtube.com/watch?v=x5w1VojBD70&feature=related
And here we are again left in 2011 with authorities spraying heavy fuel oil, the patch of oil was found on the a beach in the Bay of Plenty, New Zealand shows that without a doubt the dispersant would not work on this putty type substance.
In this case letting the oil come ashore on hard packed beaches with good access would be the best response strategy probably not the most politically correct thing to do. The dispersant will not work and the oil will come ashore so why waste time and resources causing more pollution of this sensitive area.
Dispersant is an excellent strategy when used correctly in the right place with the right oil. This type of abuse will causes problems in the future.
This sort of thing causes changes in public opinion and it bites back especially when you do it wrong and then post the evidence on the internet.
I dont know how many more photographs I will have to put on this section to illustrate this action is wrong but they just keep coming.
Used with fresh crude oil
Dispersed oil has a milky coffee appearance where the dispersant has been applied. When the dispersant is applied to a slick, the droplets of oil are surrounded by surfactant substances, stabilizing the dispersion to promote rapid dilution there is a need for water movement.
The chemical dispersants, when properly applied, can aid in the transfer to the water column large volumes of oil from the surface, obtaining results with greater speed than the traditional methods of containment and removal.
The photo right shows the plume of dispersed oil in the water column 15 minutes after the application of dispersant during a trail in the north sea (photo SINTEF). The plume looks white, this is due to colours of brown and red being lost in water below 5 meters.
The photo left shows well how quickly the action of the dispersant works when the sea conditions, oil type and dispersant type and quantity are correct.
During the Deepwater Horizon spill right, dispersant was released into the oil at the source at a depth of 1500 meters.
This was done in a obvious bid to reduce the amount of oil arriving at the surface, to date the real amount used still has not been release.
I am still of the opinion that it should not have been done at that depth as it will take much longer to break down in that environment than if it was done correctly on the surface where the fresh oil was surfacing. This was not the case as we were burning and skimming there and never saw a spray aircraft.
Unfortunately having been done once it has now become a strategy for the future.
It is known that the dispersant was Corexit 9500 which caused an uproar due to people not reading things correctly before accusing BP of using dispersant that does not appear on the UK approved dispersant list because of its toxicity.
Fact: it does not appear on the list because it failed the rocky shore test which a requirement in the UK approval procedures, this has nothing to do with its use offshore.
The EPA carried out several tests and found it was no more toxic than any of the other dispersants used.
The dispersed oil has been found suspended in plumes at great depth and appears to be breaking down more slowly than expected, a study suggested. The greatest damage to the Gulf may ultimately be in the deep sea, rather than the shorelines.
During the last two weeks of June 2010, researchers from the Woods Hole Oceanographic Institute tracked a mile-long, 650-foot-thick plume of crude oil hydrocarbons as it moved southwest of the well at a depth of about 3,000 feet. It was not the only plume, nor necessarily the largest, but its behavior may give some indication of what is happening elsewhere. Much of the spilled oil, perhaps most, may share a similar fate.
Though unable to gauge precisely how quickly oil will break down, the researchers were able to measure the activity of microbes responsible for its decomposition. It’s slow. Although the researchers said that the findings are just “a snapshot,” a “first chapter,” the results suggest that lots of oil is still in the Gulf, and will be there for a long time.
These are photos taken at different depths during the study.
Dispersants were designed for use on the sea surface, oil enters into the water colume where the majority of microbes are which help in the decomposition.
BP’s oil spill in the Gulf of Mexico this year killed countless marine animals, but it was a boon for oil-eating bacteria. The organisms, usually quiescent deep in the ocean, burst into life when the Deep Water Horizon wellhead ruptured and released a torrent of their favorite food.
A study published in the 8 October issue of Science demonstrated how quickly bacteria consumed the light crude oil. The bacteria were “fat and happy,” microbial ecologist Terry Hazen of Lawrence Berkeley National Laboratory told mongabay.com. Hazen led the study's international group of 31 researchers.
The team deployed collection canisters from ships in the gulf in May and June at 17 locations along a 30-km-long oil plume. They compared deep-water samples from inside and outside the plume. The sheer number of bacteria and the plethora of species in the plume, compared to the rest of the water, told researchers that oil was feeding the rapidly multiplying microbes. The way the oil broke down was another clue: shorter hydrocarbon chains, which microbes prefer to eat, disappeared faster.
Bacteria feasted on microscopic oil droplets like these after the Deep Water Horizon oil spill. Image courtesy of: Terry Hazen
Smaller amounts of oil have been spurting into the gulf for tens of millions of years, particularly around tectonic plate boundaries, said Hazen. Oil escapes naturally through fissures in the ocean floor. Every day, such seeps release about 1,400 barrels of oil into the Northern gulf alone, according to researchers at the Woods Hole Oceanographic Institution.
“Oil is a natural product. It’s a biological product,” Hazen said. “It doesn’t surprise us that organisms have adapted to using it over millions of years.”
The surprise, he noted, was how fast the bacteria ate the crude. Hazen’s team found the microbes’ consumption was significantly faster than expected for deep-water temperatures between 4 and 5◦C—but not fast enough to contain the spill. “Was this an ecological disaster? No doubt about it,” Hazen said.
BP used millions of liters of a chemical dispersant, called Corexit, to break up the oil gushing from the wellhead. The dispersant may have made it easier for bacteria to consume the oil, according to Hazen. Dispersed oil comprises much smaller particles than untreated oil, so bacteria can feed on more droplet surface area, you can see the oil droplets look very much like the diagram above. The scale bottom right is 20 micrometers.
The dispersant’s long-term effects are unknown, Hazen said. Toxicology tests run by the U.S. Environmental Protection Agency showed that it was toxic to at least one species of shrimp.
Despite the bacteria’s appetites, Hazen does not recommend adding foreign organisms to the sites of other oil spills. “Indigenous bugs are probably better adapted to their particular environment. Within 72 hours of a spill, their numbers will increase—anywhere,” he said. Hazen believes this kind of oil biodegradation could happen in any marine area with natural seeps.
David Valentine, a microbial geochemist at the University of California, Santa Barbara, has mixed feelings about the findings. “I think the microbiology was excellent,” he told mongabay.com in an email. However, he thinks the rate of bacterial oil consumption was slower than the study reported. “What they actually measured in nature was a combination of dilution and biodegradation, with dilution likely being the greater factor,” Valentine said.
The results of these studies will have a major point to say if this strategy is asked for in the future.
Dispersants Used at Wellhead Had Marginal Effect
07/01/2013 Spill International
The study authors are Claire B. Paris, Matthieu Le Hénaff, Zachary M. Aman, Ajit Subramaniam, Judith Helgers, Dong-Ping Wang, Vassiliki H. Kourafalou, and Ashwanth Srinivasan.
An oil-mass tracking model (the Connectivity Modeling System) simulating in three dimensions the oil discharge in deep waters at the Deepwater Horizon blowout helped to examine the possible effect of a deep water release of oil, with and without dispersants, on the oil droplet size and transport through the water column. This led to the conclusion that the amount of oil reaching the surface may have been the same, independent of dispersant application.
Scientists studying the use of subsea chemical dispersants during the Deepwater Horizon spill published their recent findings in the November 2012 issue of Environmental Science and Technology in an article entitled 'Evolution of the Macondo well blowout: Simulating the effects of the circulation and synthetic dispersants on the subsea oil transport'.
Based on fundamental oil droplet size models, the authors estimate that the turbulent discharge of oil resulted in naturally small droplets contributing to the observed deep intrusion.
Image: Simulated 3D spatial distribution of oil products below the surface based on current advection and oil buoyancy in the region. The formation of the prominent deep hydrocarbon intrusion (blue plume) and the layering of shallower plumes (cyan and green) indicate that chemical dispersants injected at the wellhead were likely not effective in changing the amount of oil reaching the surface. The oil in the top 20m of the sea surface is not shown. Image courtesy: Gulf of Mexico Research Initiative.
While oil was flowing into the Gulf of Mexico, responders injected chemical dispersants at the Macondo wellhead to reduce the amount of oil from surfacing and impacting coastal and marsh areas The numerical experiments suggested that the large fraction of gas may have caused the initial rapid surfacing of oil, due to an increase in overall buoyancy. This study revealed previously undocumented temporal aspects of the oil in the water column moved by local topographic and hydrodynamic processes.
The authors’ numerical approach provides new insights on oil transport from deep blowouts and on future subsea use of dispersant in efforts to mitigate coastal damage.
Many countries also have lists of dispersants that can be used during incidents. In the UK this list is available from MAFF (Ministry of Agriculture Fisheries and Food) and is updated every 6 months. Website below.
The products that are presently found in the world are classified as follows:
Type 1 - Conventional Dispersant
The active material has a low concentration, because of dilution in solvents, which are generally highly toxic aromatic hydrocarbons. These dispersants are not diluted before or during the application. They are rarely found nowadays.
Type 2 - Concentrated Dispersant to be Diluted in Water
The active materials are generally a mixture of tension active agents and compounds containing oxygen, among others. They are diluted when applied.
Type 3 - Concentrated Dispersant Not to be Diluted in Water
The active materials are generally a mixture of tensoactive agents and compounds containing oxygen and aliphatic hydrocarbons. This dispersant, which normally has a water base, should be applied without dilution and because it has high concentrations, results in a low consumption of the product.
In a bid to reduce the toxicity of modern dispersants, dependent on the country involved in their production the surfactant may change for those of you who have a chemical background or just to baffle the rest of us, here are some of the chemicals used in France, United Kingdom and the USA;
Alkylether or Alkylaryl Sulphate/Sulphonate, Esters of tall fatty acids, Ethoxylated Sorbitan Monooleate, Ethoxylated Sorbitan Trioleate, Ethoxylated Sorbitan Monoleate, Ethoxylated Oxtylphosphate, Ethoxylated Tridecylphosate, Polyethylene Glycol Monooleate, Polyethylene Glycol Esters of fatty acids, Sorbitan Monooleate, Sodium Diethylhexyl Sulfosuccinate, Sodium Ditridecyl Sulfosuccinate, Monolaurate Calcium Sulphonate, Monopropylene Glycol or Tall oil Esters Sorbitan, Sodium Diooctyl Sulphosuccinate, Monopropylene Glycol, Ethoxylated Sorbitan Trioleate, Ethoxylated Sorbitanoleate, Ethoxylated Octylphosphate, Ethoxylated Tridecylphosate
Method of application
The methods for the application of the dispersants in the treatment of oil slicks on the sea should be chosen taking into consideration a series of factors, among which the following merit special attention:
The type and volume of oil to be dispersed;
The degree of weathering of the oil at the moment of application;
The oceanographic and meteorological characteristics prevalent during the application and the subsequent periods;
The type of dispersant to be used;
The equipment available for application.
Besides the above, one should establish the ideal rate of application that varies according to the type of thickness of the oil in the slicks. The control of the rate of application may be done according to the flow rate of the application and the velocity of the vessel or the aircraft.
Most countries that allow the use of dispersant have rigid rules of minimum water depth this is normally 20m, minimum current speed normally 0.5 knots (1 meter per second), minimum distance from the shore or in front of offshore islands normally 2 kilometers. The amount in Litres per Hectre or Gallons per Acre. A calculation of the amount of oil to be dispersed is needed. Usually we think 1:25 or 1 part dispersant will remove 25 parts oil. This is not always the case, during the Sea Empress spill, Wales, UK on some days the rate was 1:65 and during the Captain field spill, North Sea it was 1:80. This is all dependent on the amount and type of oil as well as the type and quality of the dispersant. Obviously we try to use as little as possible in places where it will be effective.
Pump Rate (Ltrs/min)
A formular to arrive at the correct rate is: Rate of application = --------------------------------------------------------------------------
0,003 x velocity (Knots) x swath width (mtrs)
Some pumps may be speeded up or down
Velocity of vessel or aircraft may be reduced or accelarated.
Swath width is the width of spray arms, the amount of nozzels may be increased or decreased.
Some or all of the above are used to achieve theapplication rate required for the operation.
Vessels meant for this purpose should be equipped with a system composed of a storage tank for the product or a hose for direct spraying, coupled to a motor-pump set and articulated arms with spray nozzles for the spraying of the product over the oil slick. Tugboats, work boats and barges may be adapted for this operation, however, because they are relatively slow they will have better applicability in combating small-sized slicks. It is worth remembering that, in the maritime application, aerial monitoring has a fundamental role for the optimisation of the application of the dispersant, because during over flights, the denser slicks, bigger and closer to the sensitive areas, can be located with greater accuracy than maritime monitoring.
The vessel that is applying the dispersant should be guided to the best positioning during the entire operation usually from and aircraft. Communications should be maintained permanently, keeping in mind the possibility that the slick will drift because of currents or by prevailing winds.
The efficiency expected is directly associated to the operational characteristics and conditions of the system utilized that should make possible the execution of the operation in a controlled manner. In a typical installation, the arms of the system should be mounted close to the bow of the vessel at an adequate distance and height, so as to avoid that the action of the bow waves which cause repulsion and/or spreading of the oil slick, which could seriously compromise the desired results.
A typical system of spray arms for the application of chemical dispersants from vessels.
The photo right at first looks fine but if the oil were fresh enough to use dispersant then the electrics of the outboard could cause serious safety problems.
Nozzels are important to provide the desired droplet at the correct flow rate. The most common nozzel types are cone and fan shaped spray. Nozzel flow rate is determined by the size of the orifice, internal passages, liquid properties and pump pressure.
Droplet size may vary between a few microns to several hundred microns
The patten should be flat striking the water in a line perpendicular to the direction of travel. The nozzels spray angle should be fan shaped so that spray from adjacent nozzels overlap just above the water.
Since it is unusual for one nozzel to meet all requirements for droplet size and application rate manufactures normally supply a number of nozzel sets to allow for changing conditions.
This is important when systems are being used on different vessels. Nozzels with different angles and flow rates are needed to be compatable with different hull designs and distances of spray arms above the water.
The spray nozzles should be sized according to the pressure and flow rate of the pump, to make possible the uniform application of the product in the form of droplets of the correct size required for the operation and never in solid jets, mist or fog.
The application of chemical dispersant by means of the fire-fighting systems exist on some tugboats is not recommended, this alternative should only be adopted as a last resort.
In this case, the product should be sprayed over the slick with an inclination that varies between 30° and 40° in relation to the horizontal plane, keeping in mind the conditions necessary for the formation of droplets.
The photo right shows the type of nozzle used with boat spraying systems. The V should be aligned to give an even patten as in the photo above.
The photo left shows the middle nozzle mis-aligned leading to inefficient application of the dispersant.
The use of drop tubes is employed on vessels to get the nozzle closer to the water surface, it reduce the wind blowing the dispersant away.
These drop tubes may be of different lengths usually shorter towards the end of the arm to avoid nozzle dipping into the water as the vessel rolls.
The photo right shows no drop tubes, judging by the height of the vessel this spray may not reach the water surface but be blown away.
This type of airbourne dispersant may enter air intakes to the vessels engine where it may cause serious damage.
Other people do not read the litrature and produce there own system as with the photo left (thanks Thiago) where nozzles from a fire sprinkler system are being used.
As can be seen one is damaged and so the spray may look good but will not be efficient as the droplet size for putting out fires has nothing to do with dispersing oil.
This is strange as all ships are fitted with the international Storz couplings right where there are no males or females they are both the same. Who ever is ordering the system needs to ask for the connections he requires.
The photo left I took a few years ago, it demonstrate clearly that the manufacturer of the spray arm did not quite get the dimentions correct. Here it is spraying water during a test of the equipment. Dispersant is a very slippery substance so if this was dispersant the smooth aluminium deck would be covered making the working area extremely dangerous.
Elastec/American Marine; manufacturer of the Neatsweep has tried a method of using boom technology, a basic J configuration some 50 metres wide is used. At the apex there is an opening called the dispersant application zone (DAZ) where the dispersant is sprayed on to the oil through a series of nozzles as it funnels through the opening; behind this area is a plastic sheet with pockets designed to produce the mixing energy required. Dispersant is applied at the rate required for the amount of oil and the speed the vessel, by a current meter connected to the pump.
Click on the link below to see a video of a trail done at Finnmark, Norway using a boom vane to support a rope with a hose attached this effectivly extends the distance from the vessel dispersant can be sprayed. It is good to see some people are trying different ideas, though I had doubt about what sea state this could be used in.
A new concept has been tested in Norway by suspending a hose with a series of nozzles between the vessel and a mast on the BoomVane (paravane) towed by the same vessel, dispersants can be applied in a controlled manner over a wide swath. An innovative anti-tilt system prevents the BoomVane from heeling over when the nozzle hose is tightened up to the optimal catenary.Coastal - effective swath 25 m, operating speed 4-5 knots - for use with Standard BoomVane (1 m draught) on coastal fishing, patrol and work vessels.
Offshore - effective swath 50 m, operating speed 4-5 knots - for use with Offshore BoomVane (2 m draught) on offshore spill response vessels.
(www.aylesfernie.co.uk) provided the dispersant technology expertise and hardware to the project.
(www.lidanmarine.com) provided the winch technology expertise and hardware required for the advanced, automated systems to handle and maintain the nozzle hose and Offshore BoomVane in relation to the deployment vessel - also in rolling seas.
Some countries have dedicated spray aircraft dependent on their risk levels. Others use crop spraying aircraft though these
are limited to the distance offshore they can operate. It is of the utmost importance to watch the positioning of the dispersant on the slick, since it is always exposed to the action of the winds and the waves. These dynamic forces associated or not with the unfavorable meteorological conditions during the execution of the operation, can seriously compromise the expected results. It is recommended that at least 80% of the surface area of the slick is covered by the applied product starting at the leading edge where the oil is thickest.
Another important factor to be taken into consideration is the altitude, since tests of application of dispersants at altitudes on the order of 50 feet (15 m) show high efficiency, followed by tests made between 100 and 150 feet (30 and 45 m) that showed good results.
The nozzle, photo right is the type used with the ADDS pack being operated with the Hercules C130 left and as can be seen with the photo (below left) as the dispersant jet leaves the nozzle it is broken into small droplets by the wind sheer of the aircraft in flight.
This video will show you the height and speed required to use this system. It also shows that at this altitude the pilot requires a spotter plane above for his safety and for the operation to work correctly
Concentrated products should be utilized, with a kinematic viscosity above 60 cSt, since it is difficult for low-viscosity dispersants to produce the correct sized droplets in conditions that are adequate to cover the slick and mix with the oil. Other characteristics of dispersants that have an influence on the efficiency of the aerial operations are volatility, density and surface tension.
Photo right shows the spray patten behind the C130 during fight training using wate. There is a need for regular training for both air crew and response personnel. Flying at this height above the sea when your wing span is greater than your height above the water requires good coordination between all parties.
The system used with the C130 is known as Airborne Dispersant Delivery System (ADDS Pack) it is a 5,500 US gallon tank with 2 pumps and spray arms which along with 2 polystyrene crash blocks takes up the whole load bay of the aircraft.
At the moment there are 2 owned by OSRL/EARL and 1 with CCA the photo left shows it iin the load bay. When the aircraft is near the spill the tail door is opened and the arms are put out by 2 electric motors and locked into place manually. The orders to spray and stop spraying come from the spotter aircraft above.
The efficient operation of this and any system is regular training using water instead of dispersant.
The photo right shows another system known as Nimbus which is less complicated than the ADDS Pack and uses small tanks rather than one big one.
Photo left shows a dispersant spraying exercise using water we carried out in Israel where a crop spraying aircraft was modified for the job. The green flouriscene dye is the target spill for the aircraft, orange smoke flares were used to show wind speed and direction to assist the pilot. The photo was taken from the observation aircraft which is necessary during these operations.
With relation to the choice of the aircraft, one should take into consideration the capability, quantity of engines, range, cargo capacity as well as its maneuverability. Small aircrafts that can operate out of small landing fields are recommended for the response to small-sized spills close to the coast.
Helicopters offer a great advantage in terms of maneuverability being, therefore, recommended for operations in rough coastal regions and platforms for the exploration and production of petroleum. Note: the use of a platforms helipad for dispersant operations stops its use for crew movements and medivacs. Supply vessels have been used but the sea needs to be calm. From a safety point of view helecopters generate large amounts of static electricity an should be earthed before anyone touches the underslung equipment.
Photo right TC3 (UK) spray during airworthy test because this was the first time this equipment was used in this country. Finding helicopters that have hooks for under slung loads can be difficult. Do not think that because the equipment passed the air worthy test in its country of origin it will not need to pass it again in the country of operation. You may find that certain modifications will be needed to pass this test. CCA and FAA rules are different. All this can add greatly to your response times, so check before you ask for the equipment.
The parts of the nozzels used with the TC3 shown in this exploded photo (Thanks Jörg).
The yellow swirl plate left on the orginal version formed a cone. With the new version the swirl plate is gripped by the rubber washer and so forms two jets as can be seen right.
Information on operating the TC3 with a helicopter, earthing rod issues and hand signals is at the end of the Safety Section
Photo left is a Simplex (USA) spray bucket.
Below is a description that used to be on oilspilltraining.com but this site no longer exists.
The colour of the dispersed oil is very close to reality, the reason for using this is to show the comparison between the area covered by boat, helicopter or large aircraft. Just click the approprate buttons at the top the diagram.
This is done with light oils where there is no likelyhood of emulsification as in this case right where the main contamination is from aviation fuel as well as a light crude oil.
This is done by using the propellor wash from the supply vessels as they steam through the oil to break down the sheens on the water surface. This is basically mimicking a rough sea with high wave energy.
During an exercise a vessel was told from shore to disperse mechanically, the person heard disperse so they put out their spray arms to use chemical dispersant.
The Environmental Agency that was present at the time were not happy that dispersant was being used in that area. This caused financial problems for the company involved.
I said in my report that it would be better to use the word "agitation" rather than disperse mechanically to avoid any communication confusion in the future.
Evaluation of the application
The application of the dispersants should be executed together with simultaneous monitoring, with respect to the efficiency of the operation and the preservation of areas not affected by the oil.
During responses to large spills, where there is a tendency towards the formation of several slicks, monitoring should be more intensive, with the intent of defining which slicks should be treated first.
This is best for planning and guiding the application of chemical dispersants, the purpose being to estimate the volumes of oil, dimensions and positions of the slicks as well as their movement.
Monitoring should be done, preferentially, by helicopter. The aircraft should be equipped with GPS, communications system, nautical charts, tide tables, spreadsheets and photographic equipment for the registry of data and images.
Generally speaking, the aerial monitoring should include the following stages and activities:
Monitoring dispersant effectiveness at sea during the Sea Empress incident
Dr Peter Wood, Principal Consultant, National Environmental Technology Centre, AEA Technology Environment
The main approach to the clean up of oil at sea in the UK is to use approved chemicaldispersants. These are normally sprayed from aircraft onto relatively fresh oil. However, it is of critical importance to determine whether or not the dispersant is having an influence on the oil. (Not all oils are dispersible, especially once a degree ofweathering and emulsification has occurred.)
Whereas dispersed oil can sometimes be seen in the sea from vessels or aircraft this is not always the case, especially with more viscous and weathered oils where the dispersant may act only slowly. Consequently, for the first time in a major oil spill, concentrations of dispersed oil were measured during dispersant application operations.
Monitoring of the dispersion process using flow-through-flourometry indicated that the dispersant operation enhanced the rate of natural dispersion. Scientists from the National Environmental Technology Centre monitored oil concentrations at different depths under and around the oil on the sea surface. They were able to show that, at 4 m depth, oil concentrations were around <1500 μg/l in areas treated with dispersant compared to around <500 μg/l in areas that had not been treated.
This information confirmed that the dispersants were having an effect and was fed back to the response management centre. The centre was then able to continue dispersant sprayingoperations in the knowledge that the dispersants were being effective. As expected the dispersants were found to be most effective on the fresh oil emerging from the grounded tanker.
Therefore, the strategy for dispersant application was, in the first instance, to target any significant fresh releases of oil from the tanker. Once these had been successfuly treated then a secondary target was the large patches of more weathered oil. When emulsions were being treated with dispersants it was found than an initial application tended to break the emulsion while subsequent additions increased the concentrations of dispersed oil.
Part of a successful dispersion operation is the judgement of when to stop treating a particular patch of oil. In the case of fresh oil emerging from the Sea Empress, while the oil tended to remain as a coherent slick, dispersant operations reduced it thickness until only sheens remained.
In the case of weathered oil, as the successful dispersant operation progressed, the main problem became the low surface coverage of emulsion on the water surface. Once the coverage became around 30 % of the water surface it was not possible to achieve efficient application of the dispersant as so operations would terminate.
During the operations some 445 tonnes of dispersant were applied from aircraft. A notable feature of the spray response was the highly effective targeting achieved by the use of remote sensing aircraft positioned above the spray aircraft to direct the spray pattern.
This operation is well established in the UK and allows the DC3 spray aircraft in particular to target effectively ribbons of oil as narrow as 10-20 m wide.
It is difficult to estimate accurately the split between the volume of oil that would have dispersed naturally and the volume that was dispersed chemically. In total it is estimated that some 47 % (33 800 tonnes) was dispersed of which some 7200 tonnes was naturally dispersed. This means that some 26 600 tonnes was chemically dispersed.
Given that 445 tonnes of dispersant were used then this results in a ratio of 1 tonne of dispersant to 60 tonnes of oil chemically dispersed. Although this ratio is greater than that normally assumed (1 tonne of dispersant disperses 20 tonnes of oil), it is considered a reasonable estimate.
High dispersion would be expected as the dispersant was applied to fresh crude oil and the monitoring did show that successful dispersion was readily occurring.
- Survey of the distances of the slicks in relation to the closest land and the evaluation of the water depth in the area where the chemical dispersant is intended to be applied;
- An estimate of the dimensions and quantity of oil existing in each slick, especially those that are threatening sensitive areas;
- Evaluation of the prevailing meteorological and oceanographic conditions. This information will be utilised together with weather forecasts before application.
Planning and Supervision of the Operation:
- Definition of the critical slicks to be treated;
- Development of the flight plan.
- Orientation of aircraft or vessels that will apply the dispersant as well as the duration of the operation that should be initiated at the more dense leading edges of the slicks to restrict the spreading of the oil;
- Supervision of the application of the dispersant, with the intention of uniform spraying of the product;
- Orientation of the vessel or aircraft applying the product so that it maintains or corrects its position in relation to the slicks.
- The monitoring of the slicks in the process of dispersion, noting any fragmentation and the direction of their movement. This information may be employed in mathematical models for the trajectory of slicks.
During the application of chemical dispersants, observations should be performed, preferentially with boats that are capable of navigating around the slicks in a short period of time. In addition, if they have other technical restrictions, they may also aid in the mechanical agitation of oil slicks where dispersant was applied.
This monitoring is also recommended after the application of the dispersant. The objective of this is to monitor the drift of the plumes of oil dispersed in the water column in the direction of the current.
It is recommended that a collection of sediments, water, plankton and marine organisms (edible molluscs and crustaceans and any other species raised by aquaculture) be done. It is also important to sample fish caught in nets in the regions affected by the oil. Benthic fauna such as oysters and mussels are the bio indicators of oil pollution.
It is best to take at least three samples over time, with the first during the days following the application of the dispersant and the others 30 and 90 days, respectively, after the completion of the operation.
The environmental monitoring should include chemical analysis for the individual hydrocarbons, by gas or liquid chromatography, in the water column as well as in the sediment of the area where the dispersion of the oil slick was executed and in a neutral area as a base line remote location that will serve as a reference and control for any contamination.
As a biological parameter one should analyze the presence of the compounds of the dispersant applied to aquatic organisms, for example, molluscs and fishes.
In many countries, the person responsible for the application of the dispersants should submit to the appropriate Environmental Organisation a detailed plan which covers the following items;
1. Method for the collection and preservation of samples
2. Sampling program (short-, medium- and long-term)
3. The individuals responsible for the collection and analysis
4. Analytic methodology and biological and chemical parameters
5. Submit results.
The plan should evaluate the possible environmental impacts resulting from the application of the dispersant, as well as obtaining technical and scientific support data as a basis and guide for future response actions.
Testing a dispersant’s specifications and efficacy
Products are tested for conformity to the specifications outlined in Appendix A to WSL Report LR448. This includes aspects of appearance, dynamic viscosity, flash point, cloud point, miscibility and efficiency. Efficacy is determined by a standard laboritory based procedure described in WSL report LR44. The test aims to assess the proportion of the total volume of treated oil that is dispersed into the water column.
The minimum efficacy requirements depend on the type of dispersant being tested.
Type 1 (hydrocarbon solvent bases dispersant applied undiluted) and Type 2 (consentrates diluted 1:10 with sea water before application) must acheive an efficacy of 30%. Type 3(high efficacy concentrates applied undiluted) must achieve and efficacy of 60%. Copies of the test protocol discribed above is available on the MFA website by clicking the logo below.
Testing a dispersant for toxicity to marine species
There are two toxicity test:
The first aims to ensure that the relative toxicity of an oil/dispersant mixture is no greater than the toxicity of oil alone. It is called the 'Sea Test' and is carried out using the brown shrimp Cragon Cragon.
The second aims to ensure that the toxicity of the dispersant alone is not greater than the toxicity of the oil alone. This is called the 'Rocky Shore Test and is carried out using the common limpet Patella Vulgata. All products must pass both tests. Details of the test protocols are contained in the MAFF Fisheries Research Technical Report No. 102.
This can be found on the MFA website at: http://www.cefas.co.uk/publications/techrep/tech102.pdf
Comparative Toxicity of Eight Oil Dispersant Products on Two Gulf of Mexico Aquatic Test Species
Analysis of Eight Oil Spill Dispersants Using In Vitro Tests for endocrine and Other Biological Activity
It has to be said at the beginning that these types of chemicals work well in the laboratory but not always in the field
ELASTOL is a non-toxic finely powdered high molecular weight PIB polymer that dissolves rapidly in petroleum products, (gasoline, diesel, jet fuel, fuel oil, crude and etc. which I'll refer to as oil) making them viscoelastic.
The benefits of treated oil are the oil is cohesive improving oil/water separation. Treated oil resists water in oil emulsification and dispersion in the water. Cohesiveness improves containment and recovery. It enhances sorbent performance by locking in collected oil. Treated oil restricts the toxic water soluble petroleum products called BETX ( e.g. Benzene, Ethylene, toluene, and Xylenes) from dissolving into water.
The best part is that the recovered treated oil can be reused as the original product. The polymer which is a hydrocarbon is shear sensitive and can be degraded by passing recovered oil through a shear pump. treated oil can also be deluted to the point that it is no longer viscoelastic.
Oil has a high affinity for treated oil is difficult to disperse in water. This behavior is used to separate dispersed oil from water. The treated oil can also be used to remove BETX and MTBE dissolved in water. BETX is found in condensation at the bottom of large gasoline tanks and other water that has been in contact with light petroleum products for some time. MTBE is a fuel additive to add oxygen to the fuel. It has been found dissolved in ground water in California.
It is effective at very low concentrations from 100 parts per million (PPM) to 1500 PPM (.01% to .15%). It is applied as a slurry, the water acting as a transport medium. The powder floats on water, dissolving when it contacts oil. It remains effect for long periods but naturally degrades over longer periods.
Treated oil increases performance of containment and recovery equipment. Containment booms used on treated oil have higher current and tow speed capability (proven in Canadian and Norwegian open sea tests). Mechanical skimming equipment is improved 2 to 10 times it's normal rate of recovery. Drum skimmers, which are designed to recover little or no water with the oil.
When applied early reduces emulsification and dispersion of oil spills. It also reduces penetration of oil into porous soils and sandy beaches.
It's own non-toxicity and it's reduction of the toxicity of spilt oil on water make it a containment and recovery tool that is unparalleled.
A half pound treats: 100 gallons of gasoline, 200 gallons of diesel, 300 gallons of medium oil, and 500 gallons of heavy oil (the liquid version is suggested for medium to heavy oils and tank bottom water treatment)
Elastol is used in smaller quantities to increase the viscosity of lubricating oil in some applications.
This text is taken from A Review of Literature Related to Oil Spill Solidifiers 1990-2008 for Prince William Sound Regional Citizens’ Advisory Council (PWSRCAC) Anchorage, Alaska by Merv Fingas, Spill Science, Edmonton, Alberta
Literature largely focuses on potential uses, rather than actual experience. Recent use of solidifiers on very small spills appears to be successful; however, this has not been critically reviewed by independent outside parties. There are many research gaps on solidifiers, almost every aspect remains unknown. It is important to recognize that at least three fundamental types of solidifiers have been marketed. Each of these types has some what different advantages and different characteristics.
There are three types of solidifiers, polymer sorbents, cross-linking agents and polymers with cross-linking agents. The types have unique characteristics and properties. Polymer sorbents, common at this time, simply adsorb oil into spaces between polymers. Oil is only held into these spaces by weak forces. Cross-linking agents form chemical bonds between moleculesin the oil. Polymers with cross-linking agents also form chemical bonds. The latter two agentsmay react quickly and thus result in incomplete solidification if not rapidly mixed.
Reactivity and Reaction Time
Some solidifiers react so quickly that they solidify the first oil they contact and may form a crust on the oil surface. This prevents solidifier from reaching underlying oil. If this is mixed after the solidifier is expended, chunks of solidified oil will be mixed with liquid oil. Other proposed solidifiers react so slowly that they are not of use. Some agents will cross-link or react with other materials such as oil boom, docks and other organic materials. Therefore reaction time and agent reactivity are of concern.
Effectiveness is an issue with oil spill solidifiers. Many factors influence solidifier effectiveness, including oil composition, sea energy, state of oil weathering, the type of solidifier used and the amount applied. Temperature and salinity of the water may not be as important as with dispersants. More emphasis might be put on monitoring effectiveness on real applications to provide real information for assessment.
The use of solidifiers was never widespread and occurred infrequently about every 10 years since the 1960's when the notion started. The motivations for using solidifiers are: to recover oil from smaller areas quickly, to prevent the spread of slicks, to recover thin sheens and to protect areas and wildlife on a rapid basis. The issues surrounding solidifiers also remain the same; effectiveness, long-term considerations, possible toxicity, and most importantly that solidifying the oil precludes most other countermeasures. It is an important point to recognize that most other countermeasures, especially booms and skimmers, are designed to recover liquid oil. Oil weathering and oil becoming more viscous and even solid, are major problems in the oil spill business. So unless solidified oil can be easily and quickly recovered, solidification compounds the oil spill problem. This, and other factors, may restrict the use of solidifiers to small, thin and near shore spills.
There are serious research gaps which have not been addressed over 40 years since solidifiers were first proposed. Many of the questions asked about solidifiers have never been addressed by tests or research.
Utility remains a major issue with oil spill solidifiers. If solidifiers are used, this precludes the use of other mechanical countermeasures. It is important to recognize that booms and skimmers are meant to deal with liquid oil. The big problem with these recovery methods are the weathering of oil or dealing with heavier oils. More viscous and heavy oils are a major problem. Solidifying the oil, without recovering it immediately, can cause major problems. Thus solidifiers must never be used on large spills or where the oil cannot be recovered immediately. Another major issue is the completeness of solidification. Large scale tests notes two situations where this issue was raised (Walker et al., 1994). A solidifier can potentially react with the oil it first comes into contact with, leaving the remaining oil untreated. The last issue to be raised in this section is that of long-term fate and effects. The long term effects of treated or partially-treated oil have not been well studied and therefore remain largely as a topic for speculation.
It is important to understand how solidifiers work as there are several different kinds. Some of them form chemical bonds, others work only by absorbency into polymer chains. Exact details of most products are proprietary and thus only a general presentation can be made here.
This is currently the most common type of ‘solidifier’. These types are sometimes called super-sorbents, but would be best called polymer sorbents. There is no chemical bonding, van der Waals forces hold the oil between polymer strands. Many polymers have spaces between them that can hold oil. The oil can be adsorbed into these spaces. The oil is held into these spaces by van der Waals forces, which are weak attraction forces between molecules. If there was little solidifier of some types, the oil could be removed by applying pressure to the completed solid. The success of this reversal would depend on the time, as the solidified oil becomes more stable with time.
Process of Polymeric Adsorption. a typical polymer which on a micro-scale has spaces. If added to oil these polymers start absorbing oil. The final product is where the polymer matrix swells with the absorbed oil.
Many polymers are capable of being solidifiers. Generally, the block co-polymers are more efficient and hold oil better. Currently the most commonly used materials are styrenebutadiene and related polymers. Others which have been used in the past include: polytertiarybutylstyrene,
polyacrylo-nitrile butadiene, polyisoprene (rubber), polyethylene and polypropylene, poly isobutylene and related polymers.
The advantages of these types of sorbents are that they are relatively simple, probably of low toxicity and are slower to react and thus mix better. Further, these products do not link to other materials such as booms, docks, organic material or stone. The disadvantages of these type of solidifiers are that they are more like sorbents and oil can be released from these products, especially under some pressure.
Cross-linking agents are chemical products that chemically form bonds between two hydrocarbons to solidify the oil. The reaction is that of a chemical one and typically can release asmall amount of heat or absorb that amount of heat depending on the chemical used. When solidifiers were popular in the 1980's, cross-linking agents were more commonly used than polymer sorbents. One must be careful about interpreting some of the literature then as some of the tests may refer only to cross-linking agents or only to polymer sorbents or products that are a combination of both as will be described in the next section.
The Process of Cross-Linking. the cross-linking agent. Is added to oil, the agents start to crosslink various oil components. The final product is where the agent has cross-linked a portion of the oil. that starting reagent. Also it might be noted that with thick oil, the cross linking product reacts mostly with the first oil that it comes in contact with. Most cross-linking agents react quickly and thus do not penetrate very thick oil.
Cross linking agents that have been used include norbornene and anhydrides. Pelletier and Siron (1999) made a new series of oil treating agents which solidify oil. These agents were prepared by reacting surfactants, alcohols or carboxylic acids with alkychlorosilanes in light hydrocarbon solvents.
The advantages of cross-linking agents are that the final product is truly solidified (if mixed before the product reacts completely). If fully solidified, the product leaches little oil and forms a durable mat which is easy to recover. The disadvantages of this technology as that it is difficult to get complete solidification, especially of a thicker slick as the product is reactive and reacts with the first hydrocarbon it comes into contact with. Cross-linking agents also have the disadvantage of linking with other hydrocarbons such as in containment booms, docks, organic matter, etc.
Cross-Linking Agents and Polymeric Sorbents Combined
This type of agent combines a polymeric sorbent with a cross-linking agent. Often the cross-linking agent is attached to a polymer end. The purpose of this combination is to gain the advantages of both types of agent.
If added to oil these agents start to adsorb oil and cross-link various oil components. The final product is where the agent has adsorbed and cross-linked a portion of the oil. The polymers used are those described above, while the cross-linking agents are typically anhydrides.
A product called RigidOil by British Petroleum that was an agent of this type, is of interest because the composition was widely disclosed (Meldrum et al., 1981). The agent consisted of two liquids which were generally mixed shortly before applying to the oil. The one liquid consisted of a 10% maleinized polybutadiene of molecular weight 8000 with 50% of odorless kerosene plus ester, as a diluent. The other liquid consisted of a cross-linking agent, zinversate diethanolamine also in 50% kerosene/ester (9:1). Extensive testing was carried out on this product as reported in this report. The advantages of this type of solidifier agent are that the product mixes with oil better than cross-linking agent alone and that solidification, if achieved, is better than for polymeric sorbents alone. The disadvantages of this type of agent are that generally it has two components which must be mixed immediately before application and that solidification may be difficult to achieve because the product may form a crust with the oil on the top. This type of agent may also adhere to booms, docks and other carbon-containing materials.
Several field trials were carried out on the British Petroleum product, RigidOil (McGibbon et al., 1982). In 1981, 11 tests were carried out using RigidOil on 205 L light fuel oil and topped crude. The product was applied using spray booms. The North Sea was choppy throughout the tests, and thus promoted mixing. Several tests resulted in what appeared to be completed solidified oil. Some tests, however, resulted in partially-solidified oil with some free oil floating beside. In two tests the oil emulsified with water after solidifier was applied. In that same time period, a trial of RigidOil was carried out on oil-under ice in the Canadian Beaufort Sea (McGibbon et al., 1982).
The application resulted in some solidification and some free oil. It was felt that the lack of mixing was the cause of this. A test on oil on shoreline was carried out at BIOS (Baffin Island Oil Spill Study) (McGibbon et al, 1982). The agent was mixed and then applied with a hand sprayer. This resulted in the formation of a crust with little solidification of oil under the crust. It was judged that this application had little benefit. The cause was felt to be a too-rapid reaction of the agent and lack of mixing. In the mid 1980's, the BP agent was tested in larger scale by the Canadian Coast Guard and the Canadian oil industry offshore Newfoundland (Fingas et al., 1994). In these large scale tests, even more agent was required to partially solidify the oil, in fact up to 40% of the actual volume of the oil itself. This is double the laboratory requirement. Both requirements were deemed to be far in excess of what was actually practical in the event of a real spill. Crude oil was released and a ship with spray booms applied the solidifier to the oil, which was partially contained in a boom. The agent again reacted with the oil on the surface and when the oil was sampled at a later time, it was soft with some portions almost liquid. What appeared to have happened is that the surface solidified and was later mixed by waves with the liquid oil underneath. It was concluded that this technology was not practical for offshore oil spills.
Delaune et al. (1999) tested the solidifier product, Nochar A 650, by putting the granular product on oiled test plots near a shoreline. Four days after the application, the oil was removed by hand. The findings were that the solidifier did react with the South Louisiana crude forming a cohesive solid mass with no dripping. The solidified oil had a rubber-like consistency that retained its shape and could be removed by mechanical or hand means. The recovery of oil in the 3 plots ranged from 70 to 76%.The findings from the field tests are that more solidifier was required to achieve the end result than from laboratory tests. Further, in many cases, complete solidification was not achieved. This appears to be particularly the case when the oil was thick and when there was insufficient mixing energy. Near-shore tests or use appears to be more successful, especially when the slicks were thin and mixing was achieved. Caution must be used, however, in translating the test findings of one type of solidifier to another type as the three types of solidifiers behave somewhat differently. Polymeric sorbents are less likely than the other two types to form a crust and thus inhibit further solidification. Cross-linking agents are the most likely to form a crust.