Oil Spill Dispersant Fact Sheet
February, 2016
Alaska Department of Environmental Conservation
Oil Spill Dispersant Fact Sheet
What are Dispersants?
Dispersants are oil spill response tools that may
be considered for use when mechanical
equipment, such as containment boom,
sorbents, and skimmers are unable to
effectively remove free oil from water surfaces
in a timely manner. These chemical mixtures
break slicks into tiny droplets that entrain and
diffuse into the water column, using wave,
wind, and/or tidal energy. These tiny droplets
have increased surface-to-volume ratios and
can be dissolved, digested, or broken down by
natural processes such as biodegradation,
photodegradation, and reduction/oxidation to
form less stable compounds. Therefore,
dispersants do not immediately reduce the
amount of oil in the environment, but change
its distribution, persistence, and potential
effects. Droplets less than 70 microns in
diameter stay suspended, whereas larger
droplets may resurface. This reduces the risk of
oil stranding upon environmentally sensitive
areas, such as estuaries, shorelines, haul-outs,
rookeries, nearshore and intertidal areas.
Why are they used?
Dispersants are not considered to be a primary
response tool because the primary goal is to
recover and remove oil from the environment.
When this becomes unfeasible, dispersants are
one of many non-mechanical response options
that may be considered. They redistribute the
location of toxic compounds from the surface
to subsurface and produce a short-term toxicity
spike, but significantly reduce the persistence
of toxic compounds. Since mechanical
recovery has many limitations, it is not always
practical or effective. In fact, less than 20% of
crude oil is typically recovered from large,
marine spills by mechanical recovery methods.
Therefore, other response tools are considered
when mechanical recovery becomes
impractical or insufficient.
Environmental trade-offs are analyzed when
dispersant use is considered. If favored, small-
scale pilot testing must show that dispersants
are having the desired effect in prevailing
environmental conditions before large-scale
use is approved. Approval for large-scale use
must be renewed during each operational
period (typically 24 hours). Approval is only
granted after spill response managers have
coordinated with natural resource trustees and
a narrow set of conditions exist.
Test of aircraft dispersant application equipment
during CANUSDIX drill. (ADEC Photo)
Fact Sheet on Oil Spill Dispersants
February, 2016
Conditions for Use
As with all response options, dispersants have
specific conditions in which they are most
effective.
Dispersants are designed for crude oil spills
in saltwater.
Water depth must be 10 fathoms (60 feet)
or more to ensure adequate mixing depth
and minimize exposure to the ocean floor.
Wind, currents, grinding ice, and/or tidal
action must provide enough energy to mix
dispersants with oil.
Natural dispersion is favored when winds
exceed 30 mph.
Dispersant use is most effective before oil
weathers or slicks break apart (typically
within 96-120 hours after a release).
Dispersant use is discouraged near
shorelines and sensitive habitats.
Dispersant use may be preferred when
shoreline damage or harm to wildlife is
projected to exceed the risks from oil
dispersing into off-shore waters.
There must be enough dispersant on-hand
to maintain specific oil-to-dispersant ratios
for the estimated volume of oil released.
Rules for Use
Alaska law requires all companies that handle
large quantities of oil to produce an oil spill
prevention and contingency plan, or C-plan. In
order for dispersants to be considered,
companies must describe the following
response preparations in their C-plan:
1)
Means to assess environmental
consequences and ability to provide
continuous monitoring of a spill’s
environmental effects;
2)
An inventory of response equipment and
supplies, including a description of their type
and toxicity;
3)
Identification of all state/federal permits
and approvals necessary to use dispersants
along with the method and projected
timeline for obtaining these
permits/approvals after a release;
4)
A plan for protecting environmentally
sensitive areas, areas of public concern, and
the public, itself, from potentially adverse
effects of dispersants and dispersed oil.
Approval Process
The National Contingency Plan identifies the
role of key agencies when dispersant use is
considered:
The U.S. Coast Guard’s Federal On-Scene
Coordinator must approve dispersant use,
with
Concurrence from the U.S. Environmental
Protection Agency representative to the
Regional Response Team (RRT), after
Consultation with the U.S. Department of
Interior and Department of Commerce
natural resource trustees (when
practicable), and
Concurrence of the State On-Scene
Coordinator from the Alaska Department of
Environmental Conservation, when State
waters are threatened.
In order to expedite the approval process, the
Alaska Regional Response Team has developed
guidelines that include designated
preauthorization areas for dispersant use.
These guidelines can be found in the Alaska
Federal/State Preparedness Plan for Response
to Oil and Hazardous Substance
Discharge/Release (i.e. The Unified Plan) at:
http://dec.alaska.gov/spar/perp/plans/uc.htm
For more information on oil spill response in
Alaska, please visit the Alaska Department of
Environmental Conservation’s website at
http://dec.alaska.gov/spar/perp/index.htm
.