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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  sophisticated ­
  systems  with  spraying  arms  equipped  with  spraying  nozzles  used  in  the  Deepwater ­
  Florizon  incident  (US,  2010).  The  latter  systems  can  control  the  application  rate  and
nebulization  (droplet  size)  and  thus  comply  more  closely  with  the  application  recommendations. ­


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.