An odour assessment considers whether a proposed development could cause odour impacts, or whether new sensitive uses, such as homes, schools or care facilities, could be affected by an existing odour source nearby. It helps the planning authority decide whether the site is suitable for the proposed use and whether mitigation is needed to make the development acceptable in planning terms. The IAQM guidance is specifically written for odour assessment in planning, rather than environmental permitting or statutory nuisance investigations.

An odour assessment may be required where a development could release odours, or where sensitive receptors are proposed close to an existing odorous activity. Examples include wastewater treatment works, waste-handling and treatment sites, intensive animal rearing, composting, processing of animal remains, some industrial processes and rural activities such as farming or biosolids application. Assessments may also be needed where residential developments are proposed near an existing odour source, sometimes known as encroachment.

Odour risk is usually assessed by looking at the relationship between the source, pathway and receptor. The source is where the odour is released, the pathway is how it travels through the air, and the receptor is the person or place that could be affected. An adverse odour effect can only occur when all three are present. Factors such as distance, wind direction, dispersion, dilution, topography, existing controls and the sensitivity of nearby receptors are considered.

FIDOL stands for Frequency, Intensity, Duration, Odourunpleasantness and Location. These factors help assess how odour may be experienced by people. In simple terms, an odour assessment considers how often odour may occur, how strong it could be, how long it may last, how unpleasant it is, and who or what may be affected. The IAQM guidance explains that the scale of odour exposure is influenced by frequency, intensity, duration and odour unpleasantness, while the location factor reflects receptor sensitivity and local context.

No. Dispersion modelling can be useful, particularly where odour exposure needs to be predicted over a wider area or longer period. However, IAQM guidance explains that other tools may complement modelling or be more appropriate in some circumstances. These can include qualitative risk assessment, complaints review, site observations and sniff testing. For lower-risk schemes, a single assessment tool or a more qualitative approach may be enough, while higher-risk schemes may require a combination of tools.

An odour assessment report will usually describe the existing odour conditions, relevant complaints history where available, nearby receptors and their sensitivity, potential odour sources, existing or proposed mitigation measures, and the likely odour impact at sensitive receptors. Where modelling is used, the report should include enough detail on the input data and modelling choices for the results to be reproduced. The report should also conclude whether the residual odour effect is significant or not significant.

If significant odour effects are identified, the assessment should set out further mitigation or control measures that could allow the development to proceed without causing significant loss of amenity. For odour-generating developments, this may include changes to the design, operational controls, engineering controls or an Odour Management Plan. An Odour Management Plan is a live working document that explains how odour issues will be managed, controlled and reviewed on site, including normal operations, abnormal events and foreseeable incidents.