IAQM Odour Impact Assessment

Odour Impact Assessment to IAQM and EA H4 Guidance for Planning and Permitting

An odour impact assessment quantifies the likely effect of a proposed or existing activity on nearby receptors using IAQM planning guidance and, where a permit is involved, the Environment Agency H4 odour management approach. The assessment grades source odour potential, applies pathway and receptor sensitivity factors using FIDOL (Frequency, Intensity, Duration, Offensiveness, Location), and concludes on significance of effect. Where the source is high-risk or receptors are close, the assessment is supported by odour dispersion modelling outputs to give a quantitative concentration prediction at receptors.

Odour assessment for planning applications

Odour assessments support planning applications, planning objections, change of use, new developments near odour sources, and proposals involving odour-generating processes such as waste transfer, anaerobic digestion, composting, rendering, food production, MBT, sewage treatment and intensive agriculture. They are also used where new residential or sensitive receptors are proposed near an existing odour source. A planning-led IAQM odour assessment provides a defensible significance conclusion that planning officers and Environmental Health Officers can rely on, supports condition-ready mitigation, and reduces the risk of planning delays or objections.

Odour assessment for environmental permits

Odour assessments support new environmental permit applications, permit variations under the Environmental Permitting Regulations, environmental permit application support, odour management plans (OMPs), complaint investigations and direct regulator queries. Where odour is identified as a key risk in a bespoke permit, the assessment evidences how the operator will demonstrate Best Available Techniques (BAT) for odour control and meet H4 expectations on odour management, abatement performance and receptor protection.

IAQM odour assessment methodology (source-pathway-receptor)

An IAQM odour assessment uses a structured source-pathway-receptor risk model. Source potential is graded Small/Medium/Large based on activity type, throughput, abatement and odour offensiveness. Pathway effectiveness considers distance, screening, terrain, building downwash and prevailing meteorology. Receptor sensitivity is classified High/Medium/Low depending on the type of receptor and how it is used. Combining these inputs gives a risk of effect and a significance category from negligible through to substantial adverse. Where uncertainty is high, the assessment is strengthened with a site odour survey, complaint analysis or dispersion modelling.

Environment Agency H4 odour considerations

For activities regulated under environmental permits, the Environment Agency's H4 odour management approach focuses on how operators identify odour sources, control emissions, demonstrate BAT, manage sensitive receptors, respond to odour complaints and provide evidence to regulators. An H4-aligned odour assessment typically reviews the source inventory, abatement performance, management controls and any complaint history, and provides the evidence base that supports permit conditions, odour management plans and regulator engagement. It complements rather than replaces day-to-day operational odour management.

FIDOL factors explained

FIDOL is the framework IAQM and EA H4 use to describe the character of odour at receptors:

• Frequency — how often odour is detectable at the receptor
• Intensity — perceived strength of the odour when detectable
• Duration — how long each odour episode lasts
• Offensiveness — how unpleasant the odour character is (for example sewage and rendering rate as highly offensive, while bakery or brewery odours are less so)
• Location — sensitivity and type of receptor, including residential, schools, hospitals, care homes, workplaces and outdoor amenity

Odour complaints and sensitive receptors

Sensitive receptors typically include housing, schools, hospitals, care homes, workplaces, public spaces and mixed-use developments. Substantiated complaint history is treated by IAQM as direct evidence of effect and can shift the significance conclusion regardless of model predictions. Where complaints are recorded, the assessment reviews complaint logs, weather conditions at the time, source operating data and any abatement deviations to provide a credible picture of cause and effect — supporting both operator action and regulator engagement.

When odour dispersion modelling is needed

Odour dispersion modelling is added where IAQM screening indicates moderate or substantial risk, where the EA requests quantitative ouE/m3 predictions at receptors, or where source-receptor distance and meteorology make qualitative grading unreliable. Modelling typically uses ADMS with site-specific source emission rates from EN 13725 olfactometry. See odour dispersion modelling for the modelling-led workstream.

What we need from you to quote an odour assessment

• Site address and postcode
• Planning or permitting context (planning reference, EPR permit number, variation type)
• Process description, throughput and abatement
• Nearby receptors and any sensitive uses
• Complaint history if any, with dates and locations
• Proposed development or operational change
• Planning authority or Environment Agency correspondence
• Reporting deadline

Outputs and significance conclusion

• FIDOL-based source, pathway and receptor tables with explicit grading rationale
• Significance conclusion against IAQM categories from negligible to substantial adverse
• Mitigation recommendations linked to identified risk drivers
• Condition-ready wording for the LPA or EA where appropriate
• Inputs for an Odour Management Plan where required

Related odour and air quality services

IAQM significance work is often quantified through odour dispersion modelling using emission rates from EN 13725 MCERTS odour monitoring and field evidence from a site odour survey. For food sector schemes the same framework underpins our kitchen odour assessment. For planning air quality work in parallel see air quality assessment for planning, and where the output supports a permit see environmental permit application support.