Draft final

Discussion Note 9.1 GENERAL APPLICATION INFORMATION

• 
  The FOSC has final responsibility for operational aspects of dispersant applications.
  
• 
  Dispersant must only be applied by experienced spray applicators and in accordance with manufacturer instructions.
  
• 
  The persons applying dispersant are responsible for the calibration and operation of the spraying system, and the safety and maintenance of the application platform.
  
• 
  Droplet size is the key variable influencing dispersant effectiveness. Undersized droplets (e.g., fog or mist) will be lost through drift and evaporation. Oversized droplets will punch through the oil and be lost in the water column.
  
• 
  Dispersants pre-diluted in water are less effective than undiluted dispersant.
  
• 
  Only undiluted concentrate dispersant is applied from aircraft. Dispersant should, where possible, be applied into the wind and parallel with the slick.
  
• 
  Dispersant should be applied in a methodical and continuous manner to ensure the entire target area is treated.
  
• 
  Spraying effort should concentrate on the thickest sections, and/or the leading edges, of oil that threaten sensitive areas.
  
• 
  Thick portions of the slick may require several applications.
  
• 
  Oil sheen should not be sprayed with dispersant.
  

Regarding the relationship between Dispersant-to-Oil Ratio (DOR) and the concentration of oil being treated:

• 
  Regardless of DOR ratios suggested by dispersant manufacturers, there are many factors that influence dispersibility (e.g., oil characteristics, degree of weathering, water salinity, sea state) that may make it very difficult to select an appropriate DOR for the conditions faced on the day of a specific spill
  
• 
  The variability of slick thickness (or oil concentration) is such that one can never really characterize the actual oil concentration for more than a few seconds within the speed and swath constraints of a particular application system.
  
• 
  With most application systems, one is usually overdosing and under-dosing as the system moves through light, heavy and sometimes “no” oil on the water surface.
  
• 
  The best estimate of the average oil thickness (or average volume of oil per unit are) must be used.
  
• 
  Given that precise spray parameters are extremely difficult to achieve, dispersant applicators generally use about 5 gallons of dispersant per acre on their first run.
  
• 
  Area, volume and thickness can be related with the following expression:
  

10⁴ x Area (hectare) x Thickness (mm) = Volume (liters)

or

Volume (liters/Area (hectares) = 10⁴ x Thickness (mm)

► To convert liters/hectare to gallons/acre, multiply by 0.107. To convert liters/hectare to gallons/square kilometer,

multiply by 26.42.

► These values (in any units) multiplied by the DOR (as a fraction, e.g., 1:5 = 1/5 or .2) will then yield the desired dosage (in those units) for that value of DOR.

► Refer to Attachment III.a for some pre-calculated values.

From Cawthron, 2000 and Al Allen (Spilltec), 2003 personal communication

Discussion Note 9.2 AERIAL APPLICATION

This general aerial application guide is intended simply to highlight key issues. The FOSC will coordinate and oversee operational aspects of aerial dispersant applications.

• 
  Aircraft applications should always include pump-driven spray units.
  
• 
  Dispersant droplet size should be between 400 and 1000 microns.
  
• 
  Commercial aircraft spray nozzles generally range between 350 and 700 microns.
  
• 
  1000-micron spray nozzles may be needed for use on viscous oils.
  
• 
  Nozzles should achieve an application rate of 5.3 gallons per acre if using a 1:20 ratio.
  
• 
  Spray nozzles should be installed to discharge directly aft.
  
• 
  Underslung buckets on helicopters should be mounted so the pilot can see the ends of the spray booms in flight.
  
• 
  The altitude of the aircraft should be as low as possible.
  

From Cawthron, 2000

BOX 10 ARE THERE INDICATIONS THE DISPERSANT IS EFFECTIVE?

• 
  Acquire information from dispersant monitoring team (SMART team or other FOSC-designated monitors).
  
• 
  Review dispersant monitoring results after each dispersant application.
  
• 
  Determine if chemical dispersion is significantly greater than natural dispersion.
  
• 
  Assess whether changing application parameters could make the application more effective.
  

Decision: Are there indications the dispersant is effective?

• 
  Yes Go to Box 10
  
• 
  No See Discussion Note 9.2 and return to Box 8, or Go to Box 12.
  

Make a note of the decision in the Dispersant Decision Summary box on the Dispersant Use Flowchart

From Cawthron, 2000

Discussion Note 9.3 BOAT APPLICATION

• 
  Spray booms should be mounted as far forward as possible to prevent oil being moved aside by the bow wave before being sprayed. This then uses the mixing energy of the bow wave to break up the oil.
  
• 
  Spraying systems should be set so that the spray pattern is flat, striking the water in a line perpendicular to the direction of the boat’s travel.
  
• 
  The fan-shaped sprays from adjacent nozzles should be set as low as possible, overlapping just above the oil/water surface, with the inboard spray striking the hull just above the waterline.
  

Undiluted dispersants

• 
  Air blast sprayers and modified spray pumps can be used to apply undiluted concentrated dispersants and conventional dispersants.
  
• 
  Treatment rate is usually constant and determined by nozzle size and spray pressure.
  
• 
  Calibration and use of an appropriate droplet size is critical to effective applications.
  

Pre-diluted dispersants

• 
  Concentrated dispersants can be applied after pre-dilution in seawater, but will be less effective.
  
• 
  The dispersant : water ratio should be equal to, or greater than, 10%
  
• 
  Applications through ship’s fire-fighting equipment are controlled by opening or closing the dispersant supply. Vessel speed is used to control the treatment rate.
  
• 
  Dual pump systems for dispersant and seawater-supplying spray booms allow the dilution rate to be adjusted.
  
• 
  Boat speed is the main determinant of dispersant dose rate (reduce boat speed to increase the dose rate).
  
• 
  Boat speed should be in the order of 5 knots for fresh spills of liquid crude or fuel oil, which assumes that the oil has spread to 0.1 mm thick.
  
• 
  With reduced boat speeds, the required application rate per acre or km² can be maintained by reducing pump speed.
  

The following ASTM standards apply to systems involving spray arms or booms that extend over the edge of the boat and have fan-type nozzles that spray dispersant in a fixed pattern:

• 
  ASTM F 1413-92: Standard Guide for Oil Spill Dispersant Application Equipment: Boom and Nozzle Systems
  
• 
  ASTM F-1460-93: Standard Practice for Calibrating Oil Spill Dispersant Application Equipment Boom and Nozzle
  

Systems

• 
  ASTM F 1737-96: Standard Guide for use of Oil Spill Dispersant Application Equipment During Spill Response: Boom and Nozzle Systems.
  

Boat-based systems using a fire monitor and/or fire nozzle shall avoid a straight and narrow “firestream” flow of dispersant directly into the oil. There are no applicable ASTM standards for these systems at this time (December 2003).

In part from Cawthron, 2000