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Odour Impact Assessment
Smell is a very subjective thing, the nicest of smells such as baked bread or roses, would hardly be considered a problem, however the worst of smells such as rotten flesh, or rotten eggs are a real burden on the nostrils. In order to assess odour a unit has been developed, an Odour Unit (ou), 1 ou/m3 is the limit at which humans can smell an odour, dependent on its character (hedonic score) am upper limit of acceptability is then set. For live stock (chickens or pigs) the limit is set at 3 ou/m3.
|Using a computer model (or a calculator if you are particularly patient!), you can work out odour levels (concentrations) at set points away from the source (chicken shed or factory), these data points can then be used to create contour, and so gauge odour concentration at a particular point away from the source.|
From this we end up with a modeled odour plume, which can be used for
the basis of an odour impact assessment.
Of course these are modelled results, and all their aim to represent real world conditions, they will not.
Even the most complex models available and relatively simplistic in the method they use to determine dispersion of odour plumes. More complex models will use actual weather data taken from the study area to deuce likely conditions, presenting concentrations as a probabilistic concentration rather than a worst case scenario. This method is "above board" but is likely to under represent concentrations.
With sensible siting and implementation of odour management plans specific to the activity on site, odour concentration can be kept below thresholds, based on worst case scenarios.
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