CONTROLLED BURNING OF OFFSHORE OIL SPILLS

Alan A. Allen
Spiltec
Seattle, Washington U.S.A.

Abstract

The response to offshore oil spills typically involves: 1) the use of booms and skimming devices to physically recover oil; 2) the application of chemical dispersants to accelerate the breakup and natural degradation of oil; and, 3) the use of controlled "in-situ" burning, involving the containment and combustion of oil in place.  Each of these response options has its strengths and weaknesses.  Mechanical recovery, for example, provides an opportunity to actually remove oil from the water ­ this technique, however, is relatively slow, it requires a great deal of equipment and temporary storage, and often results in only a small fraction of the spill being recovered.  Dispersants provide a logistically simple and relatively fast method of accessing large areas of spillage ­ they too, however, often experience limited efficiency and may not be effective on truly thick concentrations very close to a spill source.  Controlled burning has now been recognized as another logistically simple technique, which under reasonably calm to moderate wind/sea conditions, may eliminate large quantities of oil quickly and efficiently.  The use of controlled burning, however, raises important questions about the safety of response personnel and the public, the effects of smoke and other emissions upon the atmosphere, and the feasibility of using combustion in a controlled manner along with other response options.  A careful review of the advantages and disadvantages of in-situ burning shows that there are clearly times and places where burning should be given a very high priority.  Being able to work with one or both of the other options without interference, controlled burning plays an important roll as a simple though highly effective way to remove large quantities of spilled oil with minimal risk and impact upon the environment.

1.0       Offshore Response Options

Major offshore oil spills from blowouts, subsea pipelines and tanker accidents often involve volumes of oil and areas of coverage that make their cleanup extremely difficult. With a potential spillage of 10's of thousands of barrels (i.e., thousands of tons) of oil within the first 24 to 48 hours, such spills can spread quickly to cover many square miles of ocean surface within a day or two.  Particularly in warm climates, where many oils spread quickly to thicknesses on the order of a tenth of a millimeter or less, the rate at which response systems can access the oil (i.e., the "oil encounter rate") is very low.

Traditional oil spill containment and recovery systems are often restricted to relatively narrow swaths for the interception of oil slicks.  If operated near a spill source, or in conjunction with enhanced swath capabilities (e.g., open-apex, deflection booms), such skimming systems may be able to increase their oil encounter rates significantly.  Their potential recovery capabilities may seem impressive; however, the duration of such recovery activity is usually quite short due to a lack of onboard storage capacity.  The limitations associated with storage capacity are further complicated by the uptake of water in the oil (i.e., the formation of oil-in-water emulsion).
There is a need for additional storage due to the emulsification process and because of the "free water" normally recovered with high-volume skimming systems.  Response organizations often try to deal with this storage constraint by positioning storage bladders, barges or even tankers next to or in close proximity to the skimming system.  While logical in concept, and potentially effective for some spill scenarios, this approach involves 1) a great deal of equipment, 2) a large response team with massive logistical support, 3) adequate water depths to accommodate the larger storage units, and 4) means by which recovered oil can be transferred from such storage units and disposed of.

The physical containment and recovery of spilled oil has been and always will be an important part of any response organization's plans for the handling of waterborne oil spills.  There are regions of the world and potential spill scenarios, however, where mechanical cleanup alone is either insufficient or inappropriate.  Studies have shown that other offshore response options (e.g., the application of chemical dispersants and the use of controlled "in-situ" burning) are often preferred or necessary for the rapid and efficient elimination of spilled oil (Allen, 1988; Buist et al., 1994; Fingas et al., 1994).  When oil has spread out over very large areas, for example, the use of chemical dispersants will often involve application systems that can travel at relatively high speed with broad swaths.  The resulting high a real coverage rate therefore results in a high oil treatment (or "encounter") rate.  Overall performance, of course, must then reflect the amount of dispersant that can be applied per sortie, the efficiency of the dispersant on the oil being treated, the time required to return to base for additional dispersant, and the ability to return to the right spot for continued treatment of the slick.

Helicopters, normally limited to less than 1,000 liters (i.e., a few hundred gallons) of dispersant per sortie, provide a highly maneuverable platform for the application of dispersants.  Large fixed-wing aircraft, though less maneuverable, can deliver payloads involving 10,000 to 20,000 liters (i.e., several thousand gallons) of dispersant.  The ability to treat vast quantities of spilled oil, even when spread over very large areas, makes the use of chemical dispersants a very unique and effective response technique.   Other constraints (e.g., very thick oil layers, unusually high dosages or multiple passes, water depths, etc.), however, may reduce the effectiveness of dispersants very close to a spill source.

A careful examination of the strengths and weaknesses of both mechanical removal and chemical dispersants leads one quickly to the realization of how and why the deliberate and controlled burning of spilled oil has become such an important response option (Allen and Ferek, 1993).  When a waterborne spill involves large quantities of oil that could easily exceed the recovery and/or storage capacities available, and it is essential that such quantities be captured and eliminated quickly with minimal logistical support, the controlled burning of oil "in-situ" (or, "in place") may well be the preferred response option.  A major objective of this paper is to identify the key issues involving controlled burning, and to examine the advantages and disadvantages of burning as a response option for offshore oil spills.  In order to address these issues, some of the most commonly asked questions about burning spilled oil are used as section headings.

2.0      What is in-situ burning?

In-situ burning (ISB) involves the controlled combustion of spilled oil. While ISB is commonly used in conjunction with waterborne spills, controlled combustion may also involve spills along or on shorelines, in wetland areas, on dry land, or even in containers (e.g., vessels, barges, etc.).  In-situ burning generally involves the deliberate ignition of spilled oil (or oil that is about to spill) in order to eliminate the oil before it spreads over large areas, makes contact with shorelines, and/or impacts sensitive resources.  This paper focuses on the controlled burning of oil in open-water, marine environments.

3.0       What if there is an accidental ignition of the spill source?

The tools and techniques for controlled ISB are of significant importance during such accidental marine fires.  The spillage of oil may occur so close to other facilities (docks, vessels, offshore platforms, etc.) that the deliberate ignition of the oil would not be a reasonable option.  Accidental ignition, on the other hand, could result in the loss of lives, equipment, buildings and natural resources.  By containing the burning oil with fire-resistant barriers at or near the spill source, it may be possible consume the oil at a safe distance from people, facilities, etc.

If it is not safe or practical to contain the burning oil at or near its source, the fire-resistant floating barriers (or "fire booms") could also be used downstream or downwind in order to deflect the burning oil away from populated areas or sensitive resources.  By staging fire boom at strategic locations downstream of potential high-risk spillsites, the exposure of people, vessels and facilities to fire can be substantially reduced.

4.0      Why would anyone want to conduct an in-situ burn?

The discussions at the start of this paper (under 1.0  Offshore Response Options) address some of the pros and cons of mechanical cleanup and the application of chemical dispersants.  There is clearly a time and a place for these options.  However, during moderate to large oil spills the physical removal of oil may involve a logistically complex and time-consuming response.  Even if vessels and equipment can be deployed quickly at the scene of the spill, there are significant constraints imposed by the storage volumes required for the recovered oil, emulsion and/or free water.  The time and cost to complete such physical removal operations must include all efforts to transfer the recovered oil/water, and the ultimate disposal of those fluids. 

The use of chemical dispersants can be an effective response tool; however, the treated oil and the dispersant do remain in the water column for a short time.  When applied to relatively thin films (typically hundredths to tenths of a millimeter) over large areas, the dispersed oil is normally decomposed rapidly and therefore of minimal concern at sea.  As stated earlier, the ability to treat widespread oil slicks quickly with airborne application systems is what makes chemical dispersion such an attractive response technique.  The major objective, however, is to prevent the spreading of spilled oil out over such large areas.  The containment and rapid elimination of spilled oil at or near its source before it has a chance to spread out can be achieved by burning the oil in place.  A single boom, 150-meters (500-feet) long, held in a "U"-configuration downstream of a spill source, could easily intercept and eliminate more than 100 tons (>600 barrels) of oil per hour.  This kind of oil elimination rate, free of the storage and disposal aspects of mechanical removal, can keep oil from spreading over large areas, impacting shorelines, and affecting a variety of natural resources.

5.0    What is a fire boom and how does it work?

A fire boom is a floating barrier that can deflect and/or contain floating oil while its above-water components can survive approximately 1,000oC to 1,300oC for extended periods.  Like any conventional boom, a fire boom needs to be durable, have sufficient freeboard, stability and wave-riding characteristics to contain oil with light-to-moderate waves, and be reasonably easy to deploy.  In addition to its resistance to fire, a fire boom should be able to take the simultaneous influences of: 1) bending, twisting and tension brought on by wind, waves and towing; 2) rapid cooling and heating as the water/oil interface rises and falls, and as liquid splashes against the boom; 3) penetration of oil through porous materials or joints between float segments or at connectors; and, 4) impacts with large floating debris.

A brief description of some of the more common types of fire booms is provided below:

Air Bubble & Water-Spray Systems ­ Submerged bubble injection systems, under the right conditions, could contain burning oil.  Such systems, however, are logistically complex, and require high flowrates of compressed air.  Submerged bubble barriers are normally considered as a fixed or stationary system, and fail to contain oil in currents of a few tenths of a meter per second or more.  External water-spray systems are also logistically complex; they are expensive to manufacture; and wind, waves and even low currents significantly reduce their oil herding capabilities.  If used in conjunction with a boom, the failure of a single nozzle could allow burning oil to reach the boom and/or fail to cool the boom.  Excessive quantities of sprayed water also tend to emulsify the oil to be burned and to reduce the efficiency of a burn.

Fabric Booms ­ Fire-resistant fabric booms rely upon the resistance to high temperatures of such materials as Thermoglass, K.O. Wool, Nextel, and Thermotex.  These and other high-temperature ceramic materials have been used in a number of configurations with solid flotation segments, air-inflated buoyancy chambers, and self-inflating systems.  Some of these booms involve outer fabrics that have been coated or treated to provide color, abrasion resistance, and impermeability.  Sometimes an outer "sacrificial" layer is provided that is intended to be burned off with the first exposure to fire.

Except for a modest amount of wetting provided by splashing waves, wicking and/or the effects of steam/vapors from boiling water in or adjacent to the boom, these fabric booms remain relatively dry during a burn.  A gradual embrittlement of the outer fabric over extended periods of burning will, in the presence of bending, twisting and pulling action, degrade the outer layer(s) of the boom. However, high-temperature flotation cores and fire-resistant reinforcement fabric between flotation segments can be incorporated to retain the buoyancy and oil holding capacity of the boom.  Such is the case with the Elastec/American Marine, Inc. fire boom illustrated in Figure 1.  Even with the gradual degradation of the fabric components, this boom will continue to float, and provide oil containment
at and below the water surface.

Figure 1   Elastec/American Marine, Inc. Solid-Flotation "Dry" Fabric Fire Boom

A dry fabric fire boom such as that shown in Figure 1 will sometimes experience embrittlement of its ceramic layers within  a few hours of burning.  Such degradation can be reduced by sliding the apex of a U-configuration back and forth. The apex is the downstream curve of the "U" which is often the "hottest" location along the boom.  The movement of this hot spot is accomplished by having the boom towing boats alternately speed up and slow down slightly, periodically shifting the hottest exposure point on the boom.  Even though a dry fabric boom may not provide the same thermal resistance as some other booms (e.g., steel and water-cooled systems), the advantages with certain types of deployment and use, combined with cost considerations, make it a practical and cost-effective fire boom.  A single U-configuration could be used to complete multiple burns, consuming 100s of tons (1,000s of barrels) of oil.
 
Metal Booms ­ Some metals provide outstanding resistance to fire; however, metal fire booms often lead to excessive weight, cumbersome handling and storage requirements, and difficulties in providing impermeable, flexible joints between rigid flotation segments.  Unique pleated or hinged connections are sometimes incorporated, but these components often suffer from such problems as stress cracks, distortion from continued flexing and bending, and/or leakage of oil.  Rigid metal flotation chambers and articulated flex-points for wave conformance present unique challenges as floats must not become over-pressurized from the heat, joints must flex sufficiently for both wave action and storage, and weight must be minimized to avoid handling problems and damage during deployment and recovery.  Some metal fire booms have involved highly irregular shapes that make them more susceptible to damage from impact with large objects, from tight turns around or over sharp corners, or from entanglement with lines and floating debris.

The advantages of metal fire booms include ease of cleaning and the potential for reuse.  Such booms, however, are often cumbersome to deploy and recover, they may require large storage containers, and their weight and rigidity can lead to damage and leakage from towing and wave action over extended periods of exposure.  Cost, weight and storage concerns suggest that metal fire booms might be used in the downstream apex of a towed U-configuration, while using a lighter, less expensive boom as lead boom (or guide boom) forward and along each side of the "U".  This approach would limit the actual burn area, and therefore the overall rate of oil combustion.  That is, the boom's rate of movement through the water could not be deliberately slowed to increase the burn area and thereby actually double or triple the rate of oil consumption.  Another shortcoming of this approach involves the difficulty of maintaining a burn within the limited area of the apex only.  Boom tending vessels will frequently slip forward and backward relative to each other, and winds and currents (often at different angles to the direction of tow) will move the contained oil within the boom to one side or the other.  Should conventional boom be used as the guide boom forward of the apex, it could be destroyed quickly by the burning and shifting oil layer.

Water-Cooled Fire Booms ­ For many years there have been attempts to build fire-resistant barriers that could be cooled by the wicking action of fabrics or by the constant wetting of the boom's exterior with nozzles or other types of splashing components (Buist, et al., 1994; Spiltec, 1986).  Such concepts have suffered from the limited height to which water is typically wicked by fabric, or they have become too complex and costly.  Some of these earlier water-cooled systems were too fragile to survive the waves and towing forces involved with boom towing, and they tended to emulsify the contained oil and reduce the efficiency of a burn.

In recent years, however, a totally new concept has evolved involving the use of active, internal cooling.  By distributing fresh or sea water to the interior of the boom, its outer layers can be cooled from the inside, thereby reducing the volume of water needed, while saturating the outer surface of the boom.  Manufactured by Elastec/American Marine, Inc., the Hydro-Fire boom provides an additional tool for the containment and control of burning crude oil and other flammable products.  One of the greatest advantages of the Hydro-Fire boom is its ability to keep the boom's outer cover and all internal components at or very close to the ambient sea temperature.  Such continuous cooling allows for the use of less exotic and expensive materials; it significantly increases the life expectancy of the boom; and the flotation system can now involve conventional air-filled chambers.  These characteristics provide a much lighter boom that can be stored on a reel and deployed in a matter of minutes (Figure 2 shows a cross-section of the Hydro-Fire boom).

6.0   How effective is in-situ burning?

The efficiency of in-situ burning is highly dependent upon a number of factors, including the physical and chemical properties of the oil, and the wind and sea conditions at the time of ignition.  Under the right conditions, controlled burning can remove approximately 95% to 98% of the original volume of contained oil.  As spilled oil loses its more volatile components and becomes emulsified, it becomes increasingly difficult to achieve ignition.  The burning of emulsified oils will also result in reduced efficiency, as there will be a slight increase in the amount of residue or unburned oil at the end of a burn.

Table 1 is provided as a summary of those physical and environmental constraints that most influence the potential for a successful in-situ burn.

Table 1

FAVORABLE CONDITIONS FOR IN-SITU BURNING

Minimum Oil Thickness:

·        2 to 3 millimeters (~1/10th of an inch) for fresh crude oil)

·        3 to 5 millimeters (~2/10ths of an inch) for diesel and weathered crude oil

·        5 to 10 millimeters (~1/4 to 1/3 of an inch) for emulsions and heavy fuel oils

Exposure/Evaporation:
Preferably less than 30% evaporative loss for most crude oils (normally less than 24 to 48 hours for moderate wind/seas)

Emulsification:
Preferably less than 20% water-in-oil emulsion.  For most oils between 20% and 40%, ignition will need assist with large ignition area and/or application of emulsion breaker.

Winds:
Approximately 20 knots (~37 kilometers/hour) or less.  Ignition with stronger winds may be achievable with fresh, volatile oils and/or large ignition areas.

Waves:
Approximately 1 meter (~3 to 4 feet) or less  for short-period, wind-waves.

Currents:
Less than 1 knot (~1.9 kilometers/hour) relative velocity between the surface water and the boom.  Optimum speed is between 1/2 knot and 3/4 knot.

Many crude oils, within a day or two of exposure at sea, will "weather" to a condition that may make ignition difficult to impossible.  As with all spill response techniques, timing is critical in accessing the oil as quickly as possible.  If safe to do so, oil can be contained before it spreads over large areas, loses too much of its volatile components, and takes on too much water through emulsification.  During the Exxon Valdez spill in Prince William Sound, Alaska, it is estimated that more than 100 tons (i.e., ~30,000 gallons) of crude oil were burned in less than an hour (Allen, 1990).  The burn was accomplished with approximately 137 meters (~450 feet) of fire boom, towed in a U-configuration, involving oil that had been at sea for more than 40 hours.  The burn eliminated at least 98% of the oil captured in the boom.

7.0    What are some of the most common ways to use fire boom?

Fire boom is needed in order to keep the spilled oil from spreading and thinning down to average oil thicknesses that will not support sustained combustion (typically 1 to 2 millimeters).  The objective, therefore, is to position fire boom as close to a spill source as is practical and safe to do so.  If the source is already burning, it may be feasible to surround a portion of the source with fire boom, keeping all personnel and towing vessels upwind and at a safe distance from the fire (typically 4 to 5 fire-diameters, or more).  If currents (relative to the source) are at or below 1 knot, if may be practical to "station-keep", or to hold the boom in a fixed position relative to the source.  Oil can therefore be burned at and immediately downstream of the source within the boom.

If currents are too strong to allow a "station-keeping" mode of operation, the towing boats and fire boom will have to operate in a drift mode at a safe distance downstream.  They will head toward the source, while drifting slowly backward away from it.  Oil can be captured, re-thickened within the boom, and then ignited at a safe distance.  The oil collection phase would normally be terminated when the boom reaches its holding capacity (typically on the order of 100 tons, or in excess of 500 to 600 barrels).  The collection of oil might be terminated earlier if the distance from the source becomes too great, and therefore the average oil encounter rate becomes too low.

The method and location for ignition of the contained oil will depend upon the location of the vessels and fire boom relative to other vessels, traffic lanes, drilling/production platforms and other slicks that could be thick enough to support combustion. The ignition and sustained combustion of the contained oil is planned so that it can be accomplished at a safe distance from other people, facilities and heavy slicks.  In some cases, the captured oil may have to be moved several hundred meters or more away from the slick in which it was operating to ensure that a "burn-back" of oil or a "flash-back" of vapors can not occur. The following potential burn scenarios (Figures 3­7) illustrate several representative  spill situations where in-situ burning might be implemented.

8.0    Can the ignition of oil contained in a fire boom be conducted safely?

Yes, normal procedures for the ignition of contained oil involve the use of a hand-held igniter or a helicopter-slung ignition system.  Hand-held igniters are devices that are armed and activated from a safe location upstream of the contained oil.  The igniter is released to the water at least 50 to 100 meters forward of the leading edge of the contained oil.  In this way, personnel and the vessel/helicopter from which the igniter was released are always at a safe distance when the oil is reached by the igniter.

Should the contained oil be weathered or emulsified to the point that a single hand-held igniter is insufficient to initiate combustion, a Heli-Torch is commonly used to produce a number of ignition points on the surface.  Shown in Figure 8, the Heli-Torch is an aerial ignition system that has been used for more than 20 years in numerous countries.  It releases burning globules of gelled fuel from altitudes of just a few meters to as high as 60 meters.  These globules land on the water and remain burning for 5 to 10 minutes as they drift back into the contained layer of oil.  Once again, the entire operation is conducted at a safe distance forward (and normally upwind) of the contained oil.  By the time flame reaches the oil, the helicopter and crew are well away from the burn site.

9.0  How harmful are the smoke and other emissions from an in-situ burn?

The products of combustion from a petroleum fire involve the smoke (primarily unburned carbon particulates), gaseous emissions (primarily carbon dioxide), and a small percentage of the oil left behind in the form of unburned oil and burn residue.  The unburned oil and residue is typically less than a few percent of the starting volume of oil.  It normally remains on the surface long enough to be incorporated into additional burns, or to be recovered by hand or with viscous oil skimming devices.  Even if this residue did escape removal, it would eventually break up and disperse as tar balls.  With the lighter volatiles burned from this material, it would be of relatively low toxicity and constitute a very small portion of the oil that was eliminated by burning.

It is the airborne emissions that rightfully give most people concern over the burning of spilled oil.  The major gaseous emissions are carbon dioxide and water vapor, representing about 85% of the mass of combustion products released during the burning of crude oil.  A number of minor combustion products are also produced including sulfur dioxide, nitrogen oxides, and carbon monoxide.  Some hydrocarbons are likely to escape combustion and be emitted in the smoke plume.  Polycyclic aromatic hydrocarbons (PAHs) are produced by such high temperature, oxygen-poor combustion processes; however, they are a very small portion of the vast amount of PAHs that are consumed from the original oil (Allen and Ferek, 1993).  Although these pollutants are potentially harmful, the rapid rise of the smoke plume and subsequent dilution would keep ground level concentrations well within ambient air quality standards within a very short distance from the fire.  This distance is typically well under a mile even during poor atmospheric conditions for dilution (Ferek, et al., 1997). 

One of the greatest impacts of burning oil is the visual impact created by the release of unburned carbon particulates.  Even though the plume created by these particulates represents only about 10% to 14 % of the original mass burned, it is still that which gives people nearby the impression that the smoke is harmful to the environment.  It is important to recognize that the major concern with the smoke plume involves those particles that are approximately 10 microns or less in diameter (1 micron = one millionth of a meter, or ~0.0004 inch).  Usually referred to as "PM10s", these are the particles that are small enough to lodge in the lungs and, after long periods of exposure, create health problems.  Only sensitive individuals, for example, people with existing heart or lung ailments, are likely to experience discomfort or to aggravate symptoms with any short-term exposure to high PM10 concentrations.  The key points involving the airborne emissions from burning oil are:

·        Air quality standards are normally based on conditions associated with chronic discharges.  The products of combustion from the burning of an oil spill would only occur from a highly infrequent event.

·        The products of combustion at concentrations that should be of concern for human health are only within the visible plume.  The plume can be avoided easily as it normally stays aloft, and the few people in vessels/aircraft at sea can remain well away from that plume.

·        Controlled burning provides "control" as those in charge can elect when and where to conduct in-situ burns.  Should those controls involve agreed-upon distances offshore, wind-directions for nearshore waters, or conditions under which burning would be terminated, these issues can be addressed and any concerns resolved in advance.

While not often realized, a decision not to burn an oil spill introduces its own air quality concerns.  With 30% to 50% of a
light-to-medium-weight crude oil evaporating and releasing toxic volatile organic compounds to the atmosphere, responders can be exposed to greater concentrations of pollutants (at ground level) than if the oil had been burned.

·        While a majority of any spilled oil that is burned goes off as carbon dioxide (being reminded that carbon dioxide is a greenhouse gas), it is important to recognize that the original plan for that oil (had it not been spilled) was to convert (or oxidize) a majority of it in one way or another as fuel for transportation, heating, etc.

·        All things considered, the infrequent burning of spilled oil (even on a global basis) would represent an infinitesimally small fraction of the same air pollutants created by forest fires, wood-burning stoves, auto and factory emissions, etc.

10.      Has the controlled burning of spilled oil been widely accepted?

The controlled burning of spilled oil has been recognized as a viable response technique as indicated in 100s of technical papers, and in conference proceedings and contingency plans in many countries. Burning has been used in actual spills and controlled experimental spills for well over 25 years.  Such burns have been conducted under arctic, temperate and tropic conditions, and many of them have included burns with fire boom in such places as the United States and Canada, in the North Sea off England, in Spitsbergen (north of Norway), in China, and Nigeria.  Many other countries, including Germany, Sweden, and Angola have stockpiles of fire boom, and are currently establishing plans and training programs for the use of such boom. 

Numerous other countries have individual oil companies, cleanup cooperatives and government organizations that are currently upgrading their contingency plans to include in-situ burning.  Many of these groups have already budgeted for the purchase of fire boom, ignition systems, and training programs.  Offshore exercises and drills are frequently planned and implemented throughout these regions in order to educate regulatory groups, response organizations, and the general public on the pros and cons of burning and on the protocols for conducting such operations.

At the present time, there are several efforts underway involving the planning and staging of equipment for the full-scale deployment of aircraft, vessels, fire boom and ignition systems.   In such places as Alaska and Texas (U.S.A.), Colombia, Mexico, and Russia, organizations are exploring various means by which operational guidelines can be established and field-tested  for the safest and most efficient way to conduct in-situ burns.  New products and procedures are constantly being developed and used to expand our understanding and expertise in using this response technique.  Efforts are also underway to secure authorization and support for open-water, full-scale burns involving the deliberate combustion of 100 to 200 tons (~600 to 1,200 barrels) or more of crude oil.  Such testing will provide an opportunity to evaluate the latest in fire boom design, ignition systems, and safety procedures.  Such full-scale activities will also allow for the refinement of towing maneuvers, burn enhancement and extinguishing techniques, and the training of ISB response personnel.

11.      Does in-situ burning preclude or interfere with other activities?

Done properly, the controlled burning of spilled oil should not interfere with other response activities.  Each spill situation is unique, of course, requiring careful consideration of how risks can be minimized for personnel, the environment and equipment/facilities on location.  Once determined that a burn is justified and feasible, a decision to burn should include the following additional assessments:

·        Personnel ­ Are trained personnel available to carry out an in-situ burn in a timely and efficient manner without taking those personnel away from other higher priority actions?

·        Equipment ­ Are vessels, fire boom and igniters available and capable of being moved to the spill or burn site in a timely manner?  Will vessels and/or aircraft be taken away from other higher priority actions such as personnel evacuation, spill source control, medi-vac operations, etc.?

·        Risks ­ Can the use of burning be conducted at safe distances from any other large and uncontained thick layers of oil that could accidentally be ignited?  Can the burn be conducted to avoid any accidental burning of resources and property on land or on water?  Will the smoke plume move safely above or away from response personnel and any populated areas?  Should atmospheric conditions change abruptly, can people be notified to simply move away from the smoke or remain indoors for the short duration of any possible exposure?

From a response standpoint, the use of burning is an effective way to eliminate large volumes of spilled oil quickly, efficiently and with minimal logistical support.  Two small boats with only 150 meters (~500 feet) of fire boom can remove well over 100 tons of oil per hour without any dependence on skimmers and large backup storage systems.  The containment of oil for burning can be conducted safely in close proximity to other ongoing mechanical recovery operations ­ the burning phase can then be carried out a safe distance away from any heavy slicks and any skimming operations still underway.  Mechanical recovery and in-situ burning both work best where oil slicks are the thickest and most concentrated.  If there are resources and/or time enough for only one mode of response, burning may well be the preferred response option.  If, on the other hand, both options can be used, neither one should conflict with the other.

Similar conclusions can be reached with respect to use of chemical dispersants.  While it is true that dispersants would not work well on the heavy unburned oil and residue left after burning, such use of dispersants would never be considered.  The volume of residue would be extremely small, highly concentrated, and easily recovered by a vessel assigned to that mission or by other mechanical recovery systems.  The application of chemical dispersants would normally be conducted over slicks that were located away from burning and/or mechanical recovery operations.  Since dispersant application systems have such high areal coverage rates, they might best be used to access broader regions of spillage.  Such regions might likely occur from oil that had escaped containment operations for recovery and/or burning.  Again, there are regions where each response option can work effectively and with little or no interference with other response activities.

Even if a dispersant was used upstream and closest to a source of spillage, its effects upon the oil would not interfere with any attempts to contain and burn the oil farther downstream.  In fact, the application of dispersant (assuming that it is ineffective in dispersing all of the oil) would likely enhance the chances of effectively burning any oil that remained at the surface.  That oil would be less likely to emulsify, and the presence of dispersant in it might even render the oil more flammable. 

Partially treated oil (i.e., with dispersant) might be less likely to stick to certain surfaces, including the otherwise oleophilic surfaces of such skimmers as disc, brush, drum and rope mop skimmers.  On the other hand, there are times when the partially treated oil or emulsion will actually retain, or have enhanced, its tendency to stick to certain skimming devices.  All other direct suction or weir skimming systems should in no way be hampered in recovering a floating, yet partially treated, oil layer.

12.      Does burning harm birds or marine life?

There have been no documented burns where birds or marine life (including mammals) have been attracted to the fire or smoke and thereby killed or injured by the smoke, fire or oil itself.  There are, of course, numerous examples of injury and death caused by floating oil alone.  The combustion of that oil, however, actually helps to deter such injury by creating heat or a reduction in visibility that tends to keep birds and other animals away from the contained oil.  In much the same way that free-swimming (i.e., non-planktonic) organisms seem to detect and stay away from potentially harmful (though short-duration) concentrations of dispersed oil, most birds and marine life know to stay away from fire and smoke.

Most of the heat generated during burning (~98%) is radiated up and outward from a fire.  What little heat is radiated and conducted back into the oil and surface water is used primarily to keep the oil at or above its fire point.  The heat that is passed into the water below the slick is extremely small, and rapidly dissipated by the movement of cool water (due to the towing of the boom or natural currents) beneath the fire.  Aside from the relatively few non-swimming organisms that might drift in the upper few centimeters of water directly below a burning oil slick, all other marine life will likely swim clear or never even notice the presence of a fire.

It is a fact that the burning of oil already on the sea will reduce the overall amount of toxic hydrocarbons that would otherwise evaporate into the air and dissolve into the water.  Those hydrocarbons are burned off rapidly, thereby eliminating most of them and reducing the amount of time that such pollutants would otherwise be available to impact lifeforms above and below the water.

13.      Summary of Tradeoffs involving In-Situ Burning

Tables 2 and 3 are provided as summaries of the advantages and disadvantages of in-situ burning.  A careful assessment and comparison of these factors will help reveal tradeoffs that should be considered for the controlled burning of spilled oil.

ADVANTAGES	EXPLANATION
High Elimination Rate	Nominal burn rate for relatively fresh crude oil ~0.17 m3/hr/m2 (or ~0.07 U.S.gal./min/ft2 ).  A 150-m (500-ft) fire boom with an average burn area of ~560 m 2 (~6000 ft2) could burn ~95 m3/hr (~600 bbl/hr).
High Efficiency	Typically 95% to 98%
Minimal Recovery & Storage	Nearly all of the contained oil is burned.  Minimal storage may be needed for the recovery of any unburned oil and residue.
Minimal Disposal & Cleanup	Disposal would involve only the unburned oil and residue.  The small number of boats and the booms would keep cleanup to a minimum.
Versatility	Effective on fresh or salt water; on lakes, streams, oceans; onshore or  in wetlands/marshes; and, in tropic, temperate or arctic conditions.
Possible Night Operations	Fixed, burning, continuous spill sources in relatively low currents allow for safe and effective burning in a boom nearby.
Minimal Logistics	Very few people and very little equipment needed to conduct a burn
Minimal Water Depth Constraints	Need only enough water to accommodate the draft requirements of the boom towing vessels.  Shallow-water burns are possible without boats.
Ease of Control	Burn size (or area) is easily controlled by altering speed of tow boats.  Burn can be extinguished by speeding up and entraining the burning oil beneath the boom -- can invert "U" to re-contain the extinguished oil.
Low Cost	Low manpower and equipment requirements, together with minimal recovery, storage & disposal requirements (i.e. for residue only), result in costs that are about 20% to 30% of those for other offshore options.
Minimal Environmental Impact	The potential environmental impacts of burning (i.e., smoke, gasses, heat & residue) are very small in light of their short-term, localized influences.  The location and timing of burns can be selected in order to minimize exposures to response personnel, communities and natural resources.  The rapid dilution and dissipation of combustion byproducts, together with the number and size of spill events worldwide that could be burned, suggest that the long-term effects of burning are of little consequence to the atmosphere and oceans.

DISADVANTAGES	EXPLANATION
Oil Condition Constraints	Oil must be thick enough to support combustion (i.e., at least 2-3 mm, and preferably 10 cm or more); it must be relatively low in water content (i.e., <20%-30%); and, it must contain sufficient volatiles to allow ignition and sustained combustion.
Light-to Moderate Wind & Sea Constraints	Preferably less than 20 knots (~37 km/hr) unless highly volatile with large ignition areas possible.  Short-period, wind-waves should be no more than approximately 1 meter (i.e., ~3 to 4 feet).
Need For Containment	Because of the above thickness constraints, and the tendency for oil to spread quickly, fire booms or other barriers are necessary to contain and thicken the oil throughout the combustion process.
Limited Window Of Opportunity	Because of the weathering and emulsification that occur quickly at sea, burning must be conducted as early as possible (preferably within the first 12 to 24 hours of exposure).  Very calm seas may extend "window" to 48 hours or more.  Spills in cold climates, particularly when trapped on, in or under ice/snow, burning may be conducted months or even years later.
Smoke Plume Or "Visual Impact"	The perception of most people is that black smoke is bad, especially if it is unnecessary and/or it interferes with their ability to breathe, see or function normally.  Burns need to be located and timed to avoid such impacts; and communities need to be kept informed.
Secondary Fires	In-situ burns need to be conducted well away from any offshore platforms, vessels, docks or other heavy oil concentrations to avoid an accidental ignition of other flammable materials.  The likely path and duration of a burn conducted in a towed "U"-configuration must be anticipated and monitored.
Short-Term Localized Reduction in Air Quality	Typically 85%  or more of the oil burned consists of CO2 and water vapor emissions. Particulate emissions may account for 10% to 14% of the original oil.  These and other emissions (such as CO2, SO2 or Nox) are rapidly dispersed and diluted downwind of the fire.  Significant concentrations of these emissions downstream of a burn exist for only a short time (usually only for minutes to a few hours at most).  Any fallout of particulate material is low in toxicity (compared to the original oil), and all emissions are generally released over water sufficiently removed from populated areas.

14.      References

Allen, A.A., "Comparison of Response Options for Offshore Oil Spills", Proceedings of the Eleventh Arctic Marine Oilspill Program (AMOP) Technical Seminar, Environment Canada, Ottawa, Ont., pp. 289-306, 1988.

Allen, A.A., "Contained Controlled Burning of Spilled Oil During The Exxon Valdez Oil Spill", Proceedings of the Thirteenth Arctic Marine Oilspill Program (AMOP) Technical Seminar, Environment Canada, Ottawa, Ont., pp. 305-313, 1990

Allen, A.A. and R.J. Ferek, "Advantages and Disadvantages of Burning Spilled Oil", Proceedings of the 1993 International Oil Spill Conference, API, EPA, and USCG, Tampa, Florida, pp. 765-772, 1993

Buist, I.A., S.L. Ross, B.K. Trudel, E. Taylor, T.G. Campbell, P.A. Westphal, M.R. Myers, G.S. Ronzio, A.A. Allen, and A.B.
Nordvik, The Science, Technology and Effects of Controlled Burning of Oil Spills at Sea, Marine Spill Response Corporation, Washington, D.C., MSRC Technical Report Series 94-013, 382 p., 1994.

Ferek, R.A., A.A. Allen, and J.H. Kucklick, Air Quality Considerations Involving In-Situ Burning, Marine Preservation Association, Scottsdale, Arizona, 29 p., 1997.

Fingas, M.F., G. Halley, F. Ackerman, N. Vanderkooy, R. Nelson, M.C. Bissonnette, N. Laroche, P. Lambert, P. Jokuty, K.Li, W. Halley, G. Warbanski, P.R. Campagna, R.D. Turpin, M.J. Trespalacios, D. Dickins, E.J. Tennyson, D. Aurand and R.
Hiltabrand, The Newfoundland Offshore Burn Experiment ­ NOBE Experimental Design and Overview, Proceedings of the Seventeenth Arctic and Marine Oil Spill Program (AMOP) Technical Seminar, Environment Canada, Ottawa, Ont., pp. 1053-1063, 1994.

Spiltec, Refinement of Aerial Ignition Systems (Test and Evaluation of the Heli-torch for the Ignition of Oil Slicks), Technical Report to Alaska Clean Seas, Anchorage, Alaska, 72 p., 1986.