The long-anticipated update to the original 2010 guidance introduces several key changes, from new screening distances for application in land use planning and refined assessment methodologies to enhanced tools for managing and mitigating odours. The guidance is published by Scottish environmental regulator SEPA, but is aimed at regulators, planners and industry practitioners alike – providing a strong framework for odour assessment and compliance, alongside odour management best practices.
Odour Assessment Tools and Methods
Odour screening distances
The introduction of new screening distances constitutes a major update to the 2025 guidance, where numerical limits have now been set on the acceptable range between key community elements – like homes, green areas and public amenities – and specific industrial odours. These distances, developed using Environmental complaints data, mark tangible limits on proximity between key odorous sources and potential impacts, in order to prevent complaints due to nuisance or annoyance.
Distances vary depending on industry and are currently set at 2 km for landfill sites, 1.5 km for biowaste facilities, 1 km for farming and food and drink facilities, and 500 m for waste treatment. Companies must of course take these distances into account in land use planning applications for any new facilities to be created. Odour assessments will need to be conducted early on in the site selection process, with appropriate mitigation and control measures being incorporated into the facility design.
Developers planning new residential areas will likewise need to consider odour impact, whenever these developments are proposed on land that encroaches on existing facilities located within the new set screening distances.
Odour characterisation
SEPA’s new odour guidance also provides the same extensive list of odour descriptors that featured in the 2010 version, this time accompanied by specific Odour Detection Thresholds (ODTs) for key odorous compounds. Quantifying the perceptibility of specific compounds, ODTs can be used by any business handling strong-smelling materials, allowing them to better assess the impact of operations. Changes also make it easier to determine the efficacy of current odour control measures, allowing proven methods of maintaining acceptable limits to be introduced where needed.
Regulators also benefit from the update, as ODTs provide an objective basis for assessing complaints – protecting businesses that are already compliant and reducing the number of unnecessary disputes with community members.
Hedonic tone
In addition to odour characterisation, the 2025 guidance retains the hedonic tone ranking of a wide range of common smells, which was very widely used in the 2010 guidance.
Put simply, hedonic tone is a measure of how pleasant or unpleasant an odour is to the general population – and hedonic tone rankings can be used by businesses, regulators and practitioners alike to assess odour impact and better investigate complaints. Ratings help to determine the extent of mitigation required, by clarifying the extent of a specific odour’s impact. More unpleasant smells, which generally cause annoyance and oftentimes, loss of amenity at lower concentrations, will require higher levels of mitigatory intervention than odours deemed neutral or pleasant.
Field odour assessment
The 2025 update to SEPA guidance builds on the previous version’s approach by introducing an updated framework for field odour assessment, too. As one of the particularly key assessment methods presented, this observational technique is not only used to monitor the performance of odours produced by a business but is likewise applied to complaint investigations, as well.
Departing somewhat from other published methodologies, like those in the Environment Agency and the Institute of Air Quality Management guidance, SEPA’s new field odour assessment methods introduce a key difference: the recommendation to conduct tests for 15 to 30 minutes in one single location. Other methods recommend much shorter tests of 3 to 5 minutes, recommending numerous repeat tests at different times to build up a strong evidence base, by contrast, making it interesting to see how SEPA’s new methods will pan out.
Lengthy field odour surveys like those introduced in the new guidelines have two key limitations – the first being that they restrict the number of locations that can be surveyed by a practitioner in a single visit/day – and the second being the issue of desensitisation to odours that can occur in just a few minutes, potentially affecting the assessor’s perception of any odours at play.
Odour Control Techniques
Beyond field odour assessment changes, one of the more helpful aspects of the 2025 guidelines is that they detail various odour management methods, from biofilters and chemical scrubbers to process modifications. The guidance includes advantages and disadvantages, common issues, and typical applications, making it a great tool for businesses in need of a clearer roadmap for mitigation. The techniques covered provide practitioners with proven ways to effectively control odour emissions, allowing them to determine the appropriate mitigation package for a particular process with ease.
Odour Management Plans
Finally, the new guidance provides a framework and new standardised template for Odour Management Plans (OMPs). Businesses can use these to their advantage, as standardised OMP templates are key to ensuring that all odour-related risks are systematically assessed, managed and controlled. With a standardised format, there is much less ambiguity to contend with, offering greater opportunity for consistency for all operators required to proactively assess and document their odour practices and risks. A well-structured OMP can furthermore help to avoid enforcement actions by demonstrating willingness to comply and improve, with those prepared to assess their current management strategies, invest in effective mitigation techniques and engage with odour consultants positioned to come out on top.
A mid-sized food production facility processing seafood might use the 2025 guidance to overcome previous complaints from nearby residents, for example. Once handled reactively, the company is now in a position to conduct more proactive odour assessments based on clear parameters and guidelines, leading to the installation of biofilters and ventilation systems that reduce emissions and allow the company to adjust operations accordingly. By implementing SEPA’s new OMP template, the company has not only secured compliance but also strengthened local community relations, avoiding fines and operational disruptions. This kind of forward-thinking approach will be key to businesses looking to adapt seamlessly to new regulations.
Seeking expert advice in light of the new 2025 guidelines can help businesses in all industries to secure compliance with the new framework risk free, as they implement the right, site-specific management solutions. If you are looking for advice and support on these new guidelines and how they may impact on your operations, get in touch with Logika Group to discuss your needs – contact@logikagroup.co.uk.
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