20 
Le Floch - What are Dispersants? 
Conditions for dispersant use 
Environmental conditions 
Chemical dispersion of an oil spill at sea requires a minimum level of surface agitation, i.e. a 
sea state of 3 on the Douglas Sea scale. Otherwise, droplets of dispersed oil cannot stay in 
suspension in the water column and will systematically coalesce and resurface (phenomenon 
of resurfacing). 
Several techniques have been developed to compensate for a possible lack of agitation, 
such as the use of chains towed by a ship (Figure 4.6), however success is not guaranteed 
as the resurfacing of oil droplets cannot be avoided. 
Figure 4.6: Use of chains towed by a ship aiming to introduce mechanical energy required for chemical oil 
dispersion (source: Cedre) 
Spraying 
Spraying equipment for dispersant application has considerably evolved over the years from 
simple fire hoses used in the Amoco Cadiz incident (France, 1978; Figure 4.7) to more so 
phisticated systems with spraying arms equipped with spraying nozzles used in the Deep 
water Florizon incident (US, 2010). The latter systems can control the application rate and 
nebulization (droplet size) and thus comply more closely with the application recommenda 
tions. 
Figure 4.7: Use of fire hoses for dispersant spraying in the Amoco Cadiz casualty. In retrospect, the lack 
of efficient flow control did not enable application according to the use recommendations, (source: 
Cedre). 
Nowadays, 3 rd generation dispersants can be directly applied to oil films without predilution. 
Different spraying arms are now available on the market and can be installed on ships, 
planes or helicopters.