The impact of terrain on a CBRN release

According to ATP-45. Warning And Reporting and Hazard Prediction of Chemical, Biological, Radiological and Nuclear Incidents[i], detailed weather information such as temperature, humidity, wind speed, wind direction, precipitation, and stability must be obtained to determine the effects of a CBRN hazard on the surrounding environment of the incident. Apart from the meteorological data, the impact of terrain should be considered.

The direction and speed of an airborne cloud are influenced by the nature of the terrain in the downwind area. Contaminant clouds can flow over rolling terrain, down valleys, or around buildings in urban areas. In hollows, depressions, and trenches dangerous concentrations may persist. The clouds can also encounter obstacles such as hills and tend to be slowed down by the rough ground, tall grass, and bushes. In the case of flat terrain, the movement of the contamination cloud is even and steady. A real problem may appear in an urban environment, where movement patterns may be very different, depending on buildings’ shape, heights, and other factors. Additionally, when a predominant wind switches direction in a matter of minutes, the situation becomes further complicated. In such circumstances and conditions, the cloud can be difficult to predict and model[ii].


[i] ATP-45. Warning And Reporting and Hazard Prediction of Chemical, Biological, Radiological and Nuclear Incidents (Operators Manual) (2010).

[ii] Metodyka oceny sytuacji skażeń chemicznych, biologicznych i promieniotwórczych / Ministerstwo Obrony Narodowej. Szefostwo Obrony Przed Bronią Masowego Rażenia. Chem. 408/2013.

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