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How toxic plume modelling helps incident response
In Victoria, CFA is leading the development of a toxic plume modelling capability to predict the downwind dispersion of chemicals and smoke from incidents.
By Darren Simon
This work mainly focuses on dispersion of chemicals released from hazmat or chemical, biological or radiological (CBR) incidents, as well as smoke from structure and non-structure fires such as tyre and rubbish tip fires.
Plume modelling brings together a range of information including chemical properties, topography, building data and high-resolution gridded weather forecasts. Using this data and information about the release (size, chemical type, duration) the system calculates how the substance disperses downwind.
The software helps to answer some key questions: where is the plume likely to go?; when is it likely to get there?; which areas will be most affected? See the chemical model example, above.
In addition, if detailed source information is available about the chemical and the release, modelling can also provide expected concentrations such as air quality exposure standards, explosive limits and odour thresholds.
This information will help an incident controller manage the plume hazard and helps with decision making around:
- community warnings for Shelter Indoors or Evacuation
- equipment placement on the fireground
- the location of staging and rehab areas
- deployment of atmospheric monitoring equipment. As models are a prediction, they should always be validated by atmospheric monitoring as soon as possible.
At a recent incident involving a ruptured natural gas main, plume modelling was used to provide guidance on the dispersion of the leaking gas, and helped to determine the immediate hazard area and isolation requirements. This was validated against results from onsite measurements.
The odour threshold model was particularly useful because it showed that, although there was a smell of gas in a wide area, there was no danger to the community. This prevented any unnecessary evacuations, which would have presented a greater health risk and disruption to the community than the incident itself.
The plume modelling service is available through the on-call scientific officer, who can be contacted through the rostered duty officer.
Photo by Steve Crocker, MFB