ABSTRACT
Controlled oil films from 15 through 3000 nanometers (3 microns) thick show reflectance and interference color effects that vary in an orderly way with film thickness, and that agree with the well-known table published by the American Petroleum Institute. This inherent appearance depends only upon local film thickness and is independent of oil type. Visibility of a given film is variable and is affected by ambient factors that include sky conditions, water surface state, and the depth and color of the water.
Controlled streams of 25 to 100 gpm, containing 5 to 250 ppm of oil, were discharged into Raritan Bay from a 65-foot vessel. Discharge points were above the surface or 2 to 5 feet below the surface, with the vessel an anchor in tidal currents, simulating a fixed source in a low current. Above-surface discharges were also made with the vessel underway at 6 to 15 knots. The visibility and appearance of films resulting from the discharges were recorded from the vessel and from a helicopter.
The visibility of above-surface discharges for all combinations of water rate, oil content, and vessel speed, is correlated by a Specific Oil Rate (SOR) parameter:
Discharges of SOR = 4 or less were not visible, while those of SOR = 40 or more were visible. Visibility varied for intermediate discharges in the SOR range of 4 to 40. Visibility was infrequent near SOR = 4, and became more frequent as SOR increased. Fifty percent of the SOR = 20 discharges were visible. This correlation is for observations made from an aircraft.
Results of discharges reported by the Coast Guard for vessel speeds of 10–17 kt and by the British for 8–16 kt correlate with ours via the SOR parameter. These observations were also from aircraft.
Subsurface discharges appeared substantially less visible than corresponding above surface discharges. Replication, however, was insufficient to allow development of a correlation.