2. Damage to marine fowl is avoided since oil is removed from the water surface . 

 The hazard to marine fowl that is presented by the surface oil film is eliminated 

 when the oil is dispersed as fine droplets. The droplets are initially placed 

 several feet below the water surface by the mixing process. 



3. The fire hazard from the spilled oil is reduced by dispersion of the oil 

 into the water column . The removal of this combustible material from the 

 water's surface and from contact with the atmosphere prevents possible con- 

 tamination of the spilled oil. This is perhaps the most widely recognized 

 benefit of using dispersants. It has provided the motivation in the past 

 for many instances of dispersant application, such as the previously cited 



Gulf of Mexico platform blowout, where 2,000 barrels of dispersant were applied. 



4. The spilled oil is prevented from wetting solid surfaces such as beach 

 sand, shore property, etc. As stated previously, the physical fending action 

 of a properly selected surface-active agent prevents the oil droplets from 

 wetting out on a solid surface. This is a particularly important aspect when 

 there is a substantial amount of marine sediment suspended in the water column 

 during turbulent conditions. In these cases, the untreated oil can wet the 

 sand/silt particles and settle into the sediment where it may persist as a 

 contaminant for long periods. As noted, a chemically dispersed droplet would 

 remain as a discrete droplet in the water column. 



5. The formation of tarlike residue from an oil spill is prevented . These 

 floating agglomerates range up to 10 cm in diameter. Although the origin 



of these floating tar balls has been a matter of extensive speculation recently, 

 their formation can be postulated as starting from a larger, intact mass of 

 spilled oil and weathering to a residue of only 10 to 15 percent of the original 

 volume. It is reasonable to assume, however, that if the oil had been chemically 

 dispersed in a stable manner into droplets less than 1 mm in diameter, the 

 formation of these larger agglomerated residues would be prevented. 



EFFECT OF MIXING LIMITATIONS ON USE OF DISPERSANTS 



As noted previously, 42 workboats were employed during the Torrey Canyon 

 spill, yet a substantial amount of oil came ashore. The typical manner in 

 which mixing energy can be applied by a workboat is shown in Figure 3. A 

 craft of this type traveling at 5 knots would cover approximately 35 acres 

 (14.2 ha) of water surface per hour. 



A mixing device has been developed by the Warren Spring Laboratory, 



United Kingdom, wherein a simple structure resembling a "five-bar gate" is 



towed alongside the workboat. This imparts localized surface agitation and 

 extends the mixing capability of the workboat. 



There are also instances where the use of a workboat is not a feasible 

 means of mixing because of shallow water, confined or inaccessible areas, 

 etc. In these instances, as well as in small spill applications, mixing is 

 generally accomplished by use of a fire hose. This more manual and tedious 

 approach would increase the mixing time by several fold over that attained 

 by the use of workboats. 



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