164
causes such a stable dispersion (when μ oil = 0.1Pas and σ oil = 10–6 N/m, dispersibility factor: 0.63) that additional entrainment only minimally impacts mass balance.
Although breaking waves decline even further at lower wind speeds, so does the
presence of other sea surface features that could cause additional entrainment, for
instance, Langmuir circulation (Moum and Smyth 1994).
The oil slick elongation model requires input of the oil-water interfacial tension
with or without dispersant application. The oil-water interfacial tension after dispersant application depends on success of dispersant application (logistics, targeting, incorporation into the slick, dispersant effect on oil properties). Currently no
exact data on the effective dispersant dosage in the field and resulting oil-waterinterfacial tension are readily available, partly as it depends on so many factors
(falling of the dispersant droplet, oil slick skin formation and the composition of
the oil and the dispersant) and partly as interfacial tension measurements in the lab
are highly influenced by the test settings and are not in agreement with each other.
Therefore, expert judgment is still required to parametrize this effect.
More information on the chemical effectiveness of dispersants could be
obtained via small-scale laboratory tests such as the baffled flask dispersibility
test. These easy and repeatable tests provide a measure of the susceptibility to
breakup of the dispersant-oil combination; therefore the test results provide an
indication of the change in dispersibility after addition of dispersants. The effect
of dispersants can be determined from the change in results between treated and
untreated oil.
10.4 Decision-Making About Application of Chemical
Dispersion
For selecting an oil spill response strategy, either in preparation or in active spill
situation, the implications of available response options are considered. An explicit
and structured approach to analyzing the trade-offs between strategies was formerly referred to as NEBA (net environmental benefit analysis) and recently
renamed SIMA (spill impact mitigation assessment) (IPIECA 2017). Because the
implications of dispersant application span multiple environmental compartments,
SIMA can be a particularly useful tool for this response technique.
Assessment of the extent to which application of dispersants aids mitigation of
the impacts considers three factors: (1) the logistical feasibility, (2) the effectiveness, and (3) the effects or environmental benefit. The logistical feasibility of
chemical dispersion is a practical consideration based on dispersant and equipment
stocks and the travel time to reach the slick location and will not be discussed in
this chapter. The following paragraphs summarize how to assess the effectiveness
of chemical dispersion as well as the potential environmental benefit.
M. Zeinstra-Helfrich and A. J. Murk
causes such a stable dispersion (when μ oil = 0.1Pas and σ oil = 10–6 N/m, dispersibility factor: 0.63) that additional entrainment only minimally impacts mass balance.
Although breaking waves decline even further at lower wind speeds, so does the
presence of other sea surface features that could cause additional entrainment, for
instance, Langmuir circulation (Moum and Smyth 1994).
The oil slick elongation model requires input of the oil-water interfacial tension
with or without dispersant application. The oil-water interfacial tension after dispersant application depends on success of dispersant application (logistics, targeting, incorporation into the slick, dispersant effect on oil properties). Currently no
exact data on the effective dispersant dosage in the field and resulting oil-waterinterfacial tension are readily available, partly as it depends on so many factors
(falling of the dispersant droplet, oil slick skin formation and the composition of
the oil and the dispersant) and partly as interfacial tension measurements in the lab
are highly influenced by the test settings and are not in agreement with each other.
Therefore, expert judgment is still required to parametrize this effect.
More information on the chemical effectiveness of dispersants could be
obtained via small-scale laboratory tests such as the baffled flask dispersibility
test. These easy and repeatable tests provide a measure of the susceptibility to
breakup of the dispersant-oil combination; therefore the test results provide an
indication of the change in dispersibility after addition of dispersants. The effect
of dispersants can be determined from the change in results between treated and
untreated oil.
10.4 Decision-Making About Application of Chemical
Dispersion
For selecting an oil spill response strategy, either in preparation or in active spill
situation, the implications of available response options are considered. An explicit
and structured approach to analyzing the trade-offs between strategies was formerly referred to as NEBA (net environmental benefit analysis) and recently
renamed SIMA (spill impact mitigation assessment) (IPIECA 2017). Because the
implications of dispersant application span multiple environmental compartments,
SIMA can be a particularly useful tool for this response technique.
Assessment of the extent to which application of dispersants aids mitigation of
the impacts considers three factors: (1) the logistical feasibility, (2) the effectiveness, and (3) the effects or environmental benefit. The logistical feasibility of
chemical dispersion is a practical consideration based on dispersant and equipment
stocks and the travel time to reach the slick location and will not be discussed in
this chapter. The following paragraphs summarize how to assess the effectiveness
of chemical dispersion as well as the potential environmental benefit.
M. Zeinstra-Helfrich and A. J. Murk