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Calvez  -  Decision  making  process

By  being  suspended  in  the  water  column,  such  droplets  are  expected  to  be  diluted  into  the
marine  environment  thanks  to  turbulence  and  currents.  Basically,  such  dispersion  operations
aim  at  transferring  oil  from  the  sea  surface  into  the  water  column,  “scattering”  the  slicks  into  a
more  readily  biodegradable  (i.e.  tiny  droplets  bioavailable  for  microorganisms)  form.
Other  expected  benefits  from  chemical  dispersion  are  to  mitigate  early  impacts  on  marine
fauna  using  sea  surface  (e.g.  marine  diving  birds),  to  prevent  stranding  of  persistent/emulsified ­
  slicks  on  the  shoreline  (and  related  environmental/economic  resources),  as
well  as  to  avoid  or  limit  waste  management  (e.g.  as  required  after  mechanical  recovery
and/or  shoreline  cleanup).
Nevertheless,  along  the  decision  process  those  advantages  should  be  put  into  balance  with
the  various  constraints  (e.g.  oil  type,  mixing  energy)  that  may  limit  the  efficiency  of  chemical
dispersants,  or  generate  unwanted  effects.  Regarding  this  latter  point,  the  locally  increased
concentration  of  droplets  in  the  water  column  should  be  as  transient  as  possible  (i.e.  potential ­
  for  dilution  should  be  ensured)  to  avoid  potentially  harmful/toxic  effects  on  organisms  that
would  otherwise  have  not  been  exposed/affected.  From  an  operational  point  of  view,  caution
has  also  to  be  taken  to  avoid  counteracting  with  other  response  strategies  (chemical  dispersion ­
  should  not  be  performed  in  areas  where  containment  &  recovery  operations  take
place) 3 .
In  this  context,  at  the  time  of  an  incident  the  overall  purpose  of  a  useable  decision  process  is
to  enable  relevant  authorities  to  check  swiftly  if  it  is  possible  (or  not)  to  “perform  dispersion  in
the  right  way”,  i.e.  to  verify  that  conditions  are  met  to  achieve  optimum/expected  results.
Considering  that  chemical  dispersants  are  efficient  mostly  during  the  early  stages/hours  after
the  spill,  it  is  of  utmost  importance  that  decision  is  taken  as  quickly  as  possible.  The  delay  is
dependent  on  the  degree  of  preparation  and,  also,  considerations  about  physico-chemical
(e.g.  oil  characteristics)  vs.  environmental  and  logistic  issues.
It  is  proposed  that  those  issues  are  addressed  by  answering  3  successive  questions  as  follows: ­

1.  Is  dispersion  possible?  (oil  dispersible  from  a  physico-chemical  point  of  view)
2.  Is  dispersion  acceptable?  (“beneficial”  trade-off  from  an  environmental  point  of  view)
3.  Is  dispersion  feasible?  (from  a  logistical  point  of  view)

Along  this  process,  as  soon  as  any  answer  is  ‘no’  (Figure  9.1),  response  options  other  than
chemical  dispersion  need  to  be  considered.

3  once  dispersant  is  spread  on  the  oil,  even  if  dispersion  is  not  totally  effective,  mechanical  recovery  becomes
difficult