Dispersant response

Chemical dispersants are one of the response tools available during oil spill responses.

Dispersants break up surface slicks, preventing the oil reaching coastal and shoreline environments, and reducing the direct exposure of marine mammals and birds to surface oil slicks.

The surface slick is broken up into microscopic-sized oil droplets enclosed within a film of the dispersant. These droplets are effectively weightless in water and readily disperse into the water column through wave and current energy. Here the oil is diluted many tens of thousands of times, and is eventually eaten by oil eating bacteria and other micro-organisms.

Dispersant use is provided for under the National Plan for Maritime Environmental Emergencies (the National Plan).

Strict rules and processes apply to dispersant use and only oil spill control agents (OSCA) registered products can be used. A net environmental benefit analysis (NEBA) is required to ensure dispersant is an appropriate and approved response strategy.

Monitoring oil and dispersant use ensures effective application, and dispersant use stoppage when no longer effective.

There are risks associated with dispersant use

Under the National Plan we recognise the risks, plan for them, and work to minimise their effects.

All dispersants are tested for human health effects and eco-toxicity before OSCA registration and use. Some marine areas are recognised as unsuitable for dispersant use, such as areas near particularly sensitive ecosystems including coral reefs or in shallow water where effective dilution is less likely.

We have an ongoing program to improve our knowledge of dispersants, their uses and risks. The key documents below will assist with understanding dispersants, and specifically Australia’s approach to them:

Approval and acceptance

The National Plan recognises dispersant use in maritime spills around Australia can be a very effective means to prevent major environmental damage. However, oil weathers (changes) once spilled and over time can become too viscous for dispersants to work. It is imperative that application occurs quickly.

Dispersants are tested before being accepted and purchased for National Plan response stockpiles. The oil spill control agents (OSCA) policy ensures they meet health and environmental standards.

Storage and logistics

We hold significant stockpiles of dispersants and spray equipment around the country. Some are in high risk areas to enable easy access and quick response.

To ensure rapid responses, we have 24/7 contracts with fixed wing spraying contractors using aircraft able to carry up to 3.5 tonnes of dispersant up to 350 km offshore. To assist with safety, accuracy and effectiveness, other aircraft and observers are used for on-site direction and monitoring.

Approval to apply dispersant

The use of dispersants in a National Plan response must be approved by the relevant incident controller and/or statutory authority.

The benefits to the clean-up activities and the affected environment must be supported by solid evidence from monitoring, testing and expert advice. As response circumstances change over time, approval for use is regularly re-assessed and documented.

A formal, documented process includes:

  • the need and likely effectiveness
  • expert opinion and testing
  • alternatives considered
  • environmental effects of the oil and the oil/dispersant mix
  • safety issues for the public or operators.

This is generally known as a net environmental benefit analysis (NEBA). We have a version of this for dispersant use (and other OSCAs). It is a clear, well-documented decision-making process called the Protocol for Obtaining Approval for the Application of Oil Spill Control Agents to Oil at Sea or on Shorelines.

The protocol provides simple decision-trees: one each for at sea and shoreline use, depending on what OSCA is required.

In a second stage, another simple decision-tree is used for conducting a rapid net environmental benefit assessment, adapted from international best practice. Checklists of the required processes, information and decision points complete the guideline.

Monitoring—assessing when to stop and whether it worked

Effective monitoring of dispersant use is difficult, as none, some, most or all of the oil eventually goes into the water column.

Aerial observation by trained and experienced observers is the primary means of monitoring. Reliably measuring oil in the water column is also difficult. If the dispersant worked as intended, the volumes and concentrations of oil are very low and hard to find.

We have worked with the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to develop towable measuring devices able to do in-situ, real-time oil and dispersant monitoring, and three-dimensional mapping.

Combined with the new Oil Spill Monitoring Handbook and CSIRO’s expertise in monitoring in the field, responders can now be more confident in answering the questions:

  • Did it work?
  • Should we stop spraying?
  • Where did it all go?

Understanding and communicating the benefits and risks of dispersant use

Under the National Plan, we have three main roles related to dispersants:

  • Gatekeeper—determining the acceptability of dispersants for National Plan response use under the OSCA Policy.
  • Responder—the use of dispersants in a response.
  • Advisor—we provide technical, risk and benefit information about dispersants to all other National Plan dispersant users and interest groups.

Driven by a combination of new, local and international knowledge, we are improving our knowledge of dispersants in four significant areas:

  • risk assessment
  • management
  • science
  • public information.

Foremost amongst public concerns are issues to human health and the environment.

In 2013 we started a process to identify these areas of concern by seeking the advice of two of Australia’s independent, expert bodies:

We are presenting the results of these studies as part of its commitment to being transparent and inquisitive about dispersant use as a response strategy. An AMSA preamble page has been inserted at the head of each report to ensure its context is explained and to describe how we are working with the National Plan to address the findings and recommendations.

To ensure all National Plan responders and decision-makers are aware of the risks and benefits of dispersant use, we undertake regular training and information sessions.

Information on education events, such as the National Response Team dispersant information session, is provided below. For information on the content or running of the CSIRO/AMSA dispersant masterclass, contact us.

Links for responders

Related information

Last updated: 

Thursday 17 February 2022