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Calvez - Decision making process 
corresponding window of opportunity, according to metoceanic conditions (temperature, 
wind). 
During a spill emergency, the most straightforward way to assess dispersibility of the spilled 
oil would be to perform dispersibility tests on in situ oil samples. 
Nevertheless, such field sampling may not be possible, and spilled oil viscosity should then 
be assessed according to the following steps: 
• does the viscosity of fresh oil, given sea temperature, makes it dispersible a priori 
(> or < 10,000 cSt)? 
• according to the oil pour point vs. sea temperature, is there a chance for the oil to 
stay fluid? 
• after having assessed the actual oil viscosity at sea, generally through oil weath 
ering models, is the oil dispersible at the time of dispersant application? Data from 
weathering pre-studies (dispersibility as a function of viscosity), if available, may 
be useful to answer this question. Otherwise simplified tables (expected dispersi 
bility based on oil viscosity vs. sea state) may be used. 
Figure 9.2: Detailed flowchart for Q1 “Oil dispersible from a physico-chemical viewpoint?” {Note: Yellow 
boxes indicate the information which should be, as possible, made available in NOSCP) (adapt, from Mer 
lin, 2015). 
Chemical dispersion: an environmentally “beneficial” trade-off? (Figure 9.3) 
Toxicity of dispersed oil (i.e. bioavailable small-sized droplets -typically tenths of microme 
ters) may adversely impact marine fauna and flora. For this reason, chemical dispersion is 
not applicable everywhere, and is generally not recommended : 
(i) in, or in the immediate vicinity of, ecologically vulnerable/sensitive areas, or 
(ii) in areas where renewal and mixing of water do not guarantee rapid dilution of the 
droplets. 
Also, if implemented in sheltered and/or shallow waters, dispersion process may lead to ad 
sorption of droplets on suspended matter and eventually its incorporation into sediments.