Facts About ISB

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In situ burning has been considered a primary spill countermeasure for oil spills in ice-affected waters for over 40 years, from the start of offshore exploration and production in the Beaufort Sea in the 1970s.

– Field trials at that time demonstrated on-ice burning offered the potential to remove virtually all of the oil present on the ice surface.
– Since then, numerous studies and trials have been undertaken to investigate and document burning of large crude oil slicks in arctic conditions. Nineteen of these studies involved field trials in the Arctic or experiments in test tanks with ice simulating arctic condition.
– The successful response to Macondo, through in situ burning, where more than 400 burns consumed up to 310,000 barrels of oil, proved the response technique’s effectiveness in these conditions.
– In situ burning has proved effective for oil spills in ice and has been used successfully to remove oil spills in ice-covered waters resulting from storage tank and ship accidents in Alaska, Canada and Scandinavia since the 1970s. It should be noted that most arctic drilling operations for the foreseeable future would be in open water, conditions with little or no ice.
– Low temperatures and presence of ice actually help in situ burning operations by slowing or stopping the spread of the spilled oil thus keeping it thick for efficient burning and reducing the rate at which the oil weathers
– In-situ burning consumes oil at a rate of about 3.5 mm of slick thickness per minute. For a slick the size of a football pitch (105 m by 68 m) this translates to a removal rate of 25 cubic metres per minute. This far exceeds recovery rates of even the largest oil skimmers.
– The presence of ice in concentrations over 5/10 (50% coverage) helps in situ burning operations by slowing or stopping the spread of the spilled oil, thus keeping it thick for efficient burning and reducing the rate at which the oil weathers, thus increasing the time window of opportunity for burning.
– The potential small impact from the smoke generated by in situ burning (ISB) is negligible when compared to the option of leaving the oil in place where it could cause more severe impacts.
– Intentional in situ burning operations can be conducted with minimal risk of the fire spreading uncontrollably.
– The residue from an efficient in situ burn has lost the lighter, more toxic compounds in the original crude oil and is far less toxic.

In situ burning has proved effective for oil spills in ice and has been used successfully to remove oil spills in ice-covered waters resulting from storage tank and ship accidents in Alaska, Canada and Scandinavia since the 1970s. It should be noted that most arctic drilling operations for the foreseeable future would be in open water, conditions with little or no ice.

Low temperatures and presence of ice actually help in situ burning operations by slowing or stopping the spread of the spilled oil thus keeping it thick for efficient burning and reducing the rate at which the oil weathers

Cold temperatures do not affect ignition and burning of oil slicks in ice. Experimental burns have been conducted in the Arctic at temperatures as low as -30°C.

Experimental burns involving oil saturated snow (more difficult to ignite than simple oil pools) were carried out on sea ice at McKinley Bay, North West Territories, Canada in the winter of 1979/80. The results showed that air temperatures from -31.5° to +3°C did not affect burn effectiveness.

In-situ burning consumes oil at a rate of about 3.5 mm of slick thickness per minute. For a slick the size of a football pitch (105 m by 68 m) this translates to a removal rate of 25 cubic metres per minute. This far exceeds recovery rates of even the largest oil skimmers.

The use of helicopters with equipment to ignite spills in ice conditions means that effective response can commence far sooner than deploying vessels using booms and skimmers.

Using fire booms to thicken and contain oil in open water or light ice conditions can progress faster than mechanical recovery, because burning eliminates the steps of storing and disposing of the recovered oil.

The burn rate for crude oil fires on water with diameters exceeding 3.5 m is 3.5 mm/min. Thus, for each 10,000 m2 of slick area on fire, 35 m3/min of oil is consumed. This is approximately the area inside a 300 m long section of containment boom towed in a “U” formation by two vessels. Typical, large offshore skimmers have nominal capacities in the 500 m3/hr range, or 8.3 m3/min.

For spills in a range of ice conditions, ISB using helicopters carrying a heli-torch or other approved ignitors will encounter and remove oil far faster than a vessel-based mechanical recovery effort. This advantage is primarily due to helicopters being able to quickly target and ignite widely separated pools of oil in or on the ice.

The presence of ice in concentrations over 5/10 (50% coverage) helps in situ burning operations by slowing or stopping the spread of the spilled oil, thus keeping it thick for efficient burning and reducing the rate at which the oil weathers, thus increasing the time window of opportunity for burning.

In order to target oil slicks effectively for ignition or skimming, there must be good visibility in order to see the oil and the vessels and aircraft combating the spill.

High winds and waves will prevent both slick ignition as well as the effective containment of oil for skimming.

In more open ice conditions, herding agents can be applied to rapidly thicken otherwise unignitable slicks and achieve highly effective burns.

Winds of approximately 30 to 40 km/h (15 to 20 knots) are considered to be the upper limit for ignition of oil slicks in fire booms and oiled melt pools on ice. This constraint reflects the physical processes that govern ignition, current ignition and fire-resistant booms systems, as well as the environmental conditions under which most oils will be quickly emulsified beyond a combustible state in open water. Oil encapsulated in ice will not evaporate or emulsify until it is released on to the surface of the ice the following spring. Successful and highly efficient burns have taken place with oil on the ice surface that has been allowed to weather and evaporate over 25%. Effective burning is also limited in wave heights over 1.2 metres.

Another important factor is good visibility. For a safe and effective burn to take place with fire-resistant boom or in pack ice with, or without, herders it should be possible to see:
– the oil to be collected or ignited,
– the vessels towing the fire-resistant booms, and
– the proximity of the intended burn location relative to the spill source, other vessels in the area, and other potentially ignitable slicks.

As a guide, visual meteorological conditions (VMC) that permit flying under visual flight rules (VFR) could be used. If helicopters are to be used, VMC flying conditions must exist both at the site and at the helicopter base. In Arctic areas, daylight is often extremely limited in the winter months, but exists for 24 hours per day in the summer months. Large springtime in situ burning operations to ignite oil on melt pools must factor in the availability of VMC in the window of time between when the oil begins to appear on the ice surface and when the ice sheet finally becomes rotten, breaks up, and dissipates. This time frame is usually several weeks.

The potential small impact from the smoke generated by in situ burning (ISB) is negligible when compared to the option of leaving the oil in place where it could cause more severe impacts.

In situ burning (ISB) does generate smoke however the heat from the fire lifts the smoke high into the air where it is quickly dispersed by wind. Soot concentrations in the smoke plume at sea and ground level fall below thresholds that cause human health problems within a few miles of the fire. Based on this, ISB would only be used in areas where downwind coastal communities would not be affected. The effect of in situ burning on mammals is yet to be seen. It is not likely that sea mammals will be attracted to the fire, and the effect of smoke on marine mammals is likely to be minimal. On the other hand, mammals are adversely affected by oil ingestion and oil coating of their fur; therefore, reducing the spill size by burning spilled oil can reduce the overall hazard to mammals.

Between 2% to 20% of the mass of oil consumed in an in situ burn is converted to soot particles. The amount for a given burn depends on the oil being burned and conditions such as fire size, wind speed and emulsification. The smoke plume is propelled into the atmosphere by the rapidly rising hot combustion gases, where it is dispersed by the wind. Sea and ground level concentrations of soot will fall below regulatory limits for ambient air quality within a few miles. Polynuclear Aromatic Hydrocarbons (PAHs) are generated by the “starved combustion” process involved in ISB; however, measurement and modelling studies at the Deepwater Horizon burning operations indicate that the increased risk of cancer from the PAHs is infinitesimally small.

Intentional in situ burning operations can be conducted with minimal risk of the fire spreading uncontrollably.

Lessons from 40 years of field experiments in ice conditions and those learned from the extensive burning operations at the Deepwater Horizon spill in the U.S. Gulf of Mexico have led to the development of safe operating procedures that will ensure that a planned burn does not result in secondary fires.

There is a considerable body of scientific and engineering knowledge on ISB in open water, broken pack ice and complete ice cover, gleaned from over 40 years of research, including large-scale field experiments. Flame spreading velocities as a function of oil volatility are well known, as are the heat loads produced by ISB flames.

Field experience has shown that flames will not jump from one burning pool of oil in ice to another if more than a metre separates the pools. In the case of boom failure, the oil will continue to burn uncontained until it extinguishes naturally (on the order of tens of minutes). In an ice field this would pose negligible risk of secondary fire.

The residue from an efficient in situ burn has lost the lighter, more toxic compounds in the original crude oil and is far less toxic.

The residue left after an in situ burn naturally extinguishes can be difficult to recover. However, the residue from an efficient in situ burn has lost the lighter, more toxic compounds in the original crude oil. The residue is far less toxic than the original oil and is likely not toxic to sea creatures.

The residue is much more viscous than the original oil, with a consistency ranging from roofing pitch to solid asphalt, so it does not spread out over large areas of water, and usually remains as individual mats or balls.

Although research on recovering burn residue continues, the present approach is to leave the residue and continue with further burning, in order to remove as much of the oil spill as possible from the sea surface before it contacts wildlife or reaches shore.

The loss of the lower molecular weight hydrocarbons from oil as it burns in situ both increases its viscosity and decreases its toxicity, both acute and chronic. Research has shown that the lighter ends of the oil, including the ringed compounds that are the most water soluble and acutely toxic to marine life, are greatly reduced in the residue from efficient burns.