3. Appropriate measures for odour management
Source: gov.uk (2025-12-03)

The basic odour control measures you must use for any regulated activity.

You need to:
- apply comprehensive and cost-effective odour control measures to manage your site effectively and efficiently
- have more controls if there are risk factors, such as people visiting, living or working close to potentially odorous (smelly) sites
Using ‘appropriate measures’ requires a proportionate and balanced approach which is:
- not more costly than necessary
- does not compromise one environmental outcome for another
- allows for effective site operations
Sometimes, you can get acceptable results through strict inventory or process controls rather than complex or expensive equipment.

You should also check if there’s technical guidance for your industry sector (https://www.gov.uk/government/collections/technical-guidance-for-regulated-industry-sectors-environmental-permitting) on best available techniques (BAT) and appropriate measures.

Controlling materials on site

You must base your appropriate measures for controlling odour pollution on the characteristics of all materials identified in your risk assessment (https://www.gov.uk/guidance/risk-assessments-for-your-environmental-permit).

Many regulated processes manage odorous or potentially odorous materials. You must make sure your capacity limits (quantities) are realistic and that you keep to them at every stage of the process. These quantities are not the annual tonnage limits stated in your permit.

You must never receive materials on site unless you have capacity for managing them effectively.

Procedures for receiving materials

You must not receive materials which are highly odorous, or have the potential to become highly odorous, unless you are able to store and process them while controlling odorous emissions.

You must understand the odour potential of all materials you will accept to ensure that appropriate controls are put in place.

Important factors will include:
- the process generating the material (including any treatment and storage before arrival)
- packaging
- age
- temperature
- moisture
Some materials may not be particularly odorous when you receive them. But they may have the potential to be when stored and treated at the site.

Site workers may:
- be unable to detect any odorous emissions
- perceive them less strongly
- not find them as offensive due to their adaptation to the odour
Site workers should avoid deliberately sniffing waste as it may harm their health.

It is good practice to decide in advance:
- if you can receive and manage the material at the site
- how you’ll manage the material to control odour pollution
- what checks, tests, records, or decisions you need to be make for each load as it arrives
Additional requirements for how you receive waste

You must document:
- how you decided to receive specific waste streams from individual customers
- any special measures you plan to manage these wastes to control odour pollution
You must complete acceptance decision records for each waste stream before you receive any shipments.

These waste stream acceptance decision records should include:
- waste stream description, including all information provided by the customer
- any previous odour problems experienced from receipt of this waste
- supplier or sources
- process generating the waste and any relevant treatment history
- where the waste is to be stored after you receive it
- maximum storage times before treatment
- maximum quantities allowed in storage or treatment
- any relevant storage conditions required
- any odour related treatment, containment, and abatement measures
- any identification, verification or condition tests which need to be carried out on each shipment upon receipt
- any decisions you will need to take after receiving individual shipments, such as verification testing, relevant storage, and treatment capacities available at the time
Your acceptance decision records must be certified by a named, competent and responsible person and confirm:
- enough information is available to them to work out if the site infrastructure and processes can manage the waste type
- you will be able to minimise odorous emissions
- you will not cause serious odour pollution
Completing these assessments in advance will help avoid:
- rushed decision making
- unnecessary transport for rejected materials
If you do not have enough information about a waste stream, you should base the way you receive and manage the waste on reasonable worst-case assumptions. For example, if you do not know the age or state of decay of material, you should assume it is decomposing and odorous.

Waste producers who misrepresent their materials in a way which causes an operator to breach their permit may be guilty of an offence. Misrepresentation may include not telling the operator about any relevant changes to a waste stream, such as its degree of decomposition.

Inventory controls

Your management system must include a storage plan. This is specified in the management system guidance (https://www.gov.uk/guidance/develop-a-management-system-environmental-permits).

Factors such as storage times and quantities are directly relevant to odour control.

You must maintain an inventory control system which:
- documents material receipts and movements
- can be audited
- documents compliance with receipt, storage and treatment limits in the permit
- shows that holding times are minimised when needed to control the odour potential for materials
- documents compliance with realistic capacity limits for each storage location or treatment process
Follow the develop a management system (https://www.gov.uk/guidance/develop-a-management-system-environmental-permits) guidance on what to include in a waste storage plan.

You must apply inventory controls to all materials on site according to the odour risk they create at that point in the process. This includes:
- materials waiting to be processed
- materials being processed
- materials between processes
- waste or by-products
- finished materials
Housekeeping, vehicles and containers

You must:
- have housekeeping procedures in place to promptly clean any exposed contaminated surfaces (floors, walls, equipment and so on) to a standard suitable to minimise odorous emissions
- have procedures for inspecting and cleaning spills, drains and sumps which could cause odorous emissions
- ensure there are satisfactory cleaning arrangements for vehicles or containers delivering odorous materials – both shortly after they are emptied and before they are released from containment areas
- maintain auditable records of inspections, cleaning efforts and results
Process controls

Some materials may be inherently odorous. For example, those in waste treatment, food processing or animal rendering. But you must use effective process controls to prevent them becoming more odorous than necessary.

The way you manage materials, including wastes, can have a strong influence on how quickly odorous chemicals are broken down. Poor handling conditions can greatly increase the odour potential of materials. This can be through:
- the build-up of intermediate breakdown products
- the production of anaerobic decomposition products, such as reduced sulphur compounds
Use the specific guidance on process controls in the technical guidance for your industry sector (https://www.gov.uk/government/collections/technical-guidance-for-regulated-industry-sectors-environmental-permitting) or BAT conclusions.

Evaporation controls

Odorous chemicals can only be detected after they are evaporated into the air. They will not be detected while in liquids or solids. Many of these chemicals will be dissolved in water layers and released when that water evaporates.

For some processes, such as drying pet food or waste composting, this change of state is a necessary part of the process. However, in other situations you can reduce evaporation by:
- avoiding unnecessary disturbance
- minimising temperatures (such as keeping materials out of direct sunlight)
- chemical treatment (such as control of acidity (pH))
- barriers (such as covers, clean water layer, foams, surface chemical treatments)
If you need to use evaporation controls, you must apply them in a way which avoids causing a loss of process control, as this may result in greater odorous releases later. For example, a physical cover over biowaste may temporarily reduce evaporation. However, this can cause anaerobic conditions and produce more odorous chemicals which are released when the material is disturbed.

Containment

If containment is required, you must:
- use a combination of engineered infrastructure and procedures which make the containment features work
- use appropriate monitoring to manage containment and show that your controls are working
Aside from sealed vessels, engineered containment systems work by 2 mechanisms.

1. Reduced interior pressures (negative pressure) are intended to control emissions in dynamic containment systems.

This approach aims to create a consistent flow of air into the containment feature. These air flows will be through designed or unavoidable openings by abstracting odorous indoor or contained air to abatement. On its own, this approach provides only limited benefit at a high cost as it requires the containment system to be maintained to a high standard while allowing access.

2. The number of air changes per hour is one important indicator for ventilation systems based on dilution containment.

This approach requires engineered enclosures, such as buildings, to be ventilated to abatement to reduce levels of odorous chemicals in the enclosure. In this way, small or short-term releases of less odorous air from the enclosure, such as when doors are opened, will have a greatly reduced offsite odour impact.

Adequate ventilation can also:
- improve visibility within buildings that are dusty or foggy
- improve temperature control
- reduce degradation of building materials
- improve conditions for workers
Dilution containment may help to control the risks to staff described in the Control of Substances Hazardous to Health Regulations 2022 (COSHH) and the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).

You must never try to meet containment requirements in a way which requires illegal and unsafe working environments.

Dynamic and dilution containment approaches are complementary, and you can combine them to improve their effectiveness and reduce cost.

Example of combined approaches

An enclosed waste trommel might operate on dynamic containment principles but also be inside a building operating under dilution containment principles. This can improve efficiency because any air extracted from within the trommel will limit emissions into the building and help ventilate it as well.

Air quality within the building can be improved as releases from the feature (in this example a trommel) into the building will be greatly reduced. Dynamic containment of the trommel will be more effective because wind speeds within the building will be very low.

Some materials may lend themselves to other containment strategies. For example, negative aeration has been used on compost in open bays. These solutions must be carefully designed to maintain good process control conditions and avoid releases when the material is moved.

In special circumstances, such as some poultry abattoir lairages, it may be possible to use containment directly ventilated to enhanced dispersion, such as a tall stack. However, most containment features will need suitable ventilation and abatement systems which work together.

Whatever containment method or combination of methods you use, you must consider the risk of episodic (occasional) emissions.

Short-term peaks of emissions are likely to be more annoying for people who live or work nearby. This might be caused by activities such as opening doors to a building containing odorous materials, or the disturbance of compost when turning, moving or screening.

Abatement

You may find established abatement methods which are suitable for specific applications in sector BAT conclusions. For example, the use of biofilters at aerobic composting sites. These abatement systems must be tailored to meet the specific requirements of your site. This includes contaminant loading rates, air flow rates, maintenance and monitoring to ensure satisfactory performance.

If your application is not covered by relevant sector BAT conclusions, you will need to clearly understand the chemical nature and physical characteristics of air to be treated to select a suitable abatement method or combination of methods. This includes:
- both odorous and non-odorous components
- oxygen levels
- temperature
- humidity
As with established application-specific abatement methods, you need to consider:
- chemical loading rates
- overall capacity
- air flow rates
- other constraints of the abatement approach
You will also need to produce a performance monitoring plan, tailored to your abatement method and application.

Compatibility of equipment and methods

When the Environment Agency reviews your odour management plan, they will consider the suitability of your containment and abatement systems.

Containment and abatement systems must be designed to work together. You must consider their respective capabilities and limitations. For example, containment systems may require a minimum air flow for them to be effective. But excessive air flows through scrubbers may make them ineffective. Abatement systems may also have temperature or humidity limits for effective operation.

Some abatement techniques may not always be available when needed. For example, engines or boilers may provide excellent abatement for some low volume odorous air streams but not operate continuously. You may need to take other abatement systems out of service for maintenance.

You will need to provide effective backup odour control measures for continuous emissions control.

Large or complex sites may need to control a range of different sources of odorous emissions. These sources may:
- have different chemical components, physical characteristics (temperature or humidity), volumes and concentrations
- be separated by long distances
Combining air streams with dramatically different flow, chemical, location and physical characteristics can increase the cost and reduce the effectiveness of an abatement system.

You should consider using multiple smaller abatement systems which are designed to treat individual air streams. In some cases, it may be appropriate to provide tailored pre-treatment of individual sources before combining air streams for final treatment. Combining abatement technologies can also be better and more cost effective in some instances.

Engineering and performance monitoring

You must provide clear and detailed plans to show air flow rates through ducts and containment features, such as buildings.

Your system should introduce fresh air in one part of a containment feature and odorous air extracted from a location away from this. The point of introduction should normally be at or near doors which regularly need to be opened for access.

Your plans should consider natural tendencies, such as the reduced density of hot compared to cold air, and humid compared to drier air.

If your air handling system is large or complex, your containment systems must have more detailed engineering assessments. Where relevant, you should apply ventilation principles identified in the Health and Safety Executive (HSE) local exhaust ventilation guidance (https://www.hse.gov.uk/lev/). You should also apply advice from the HSE guidance on the effective commissioning of ventilation systems.

Some air handling systems will be affected by highly contaminated, corrosive and humid conditions which can lead to rapid deterioration of their performance.

Containment and abatement systems may operate under highly variable conditions, such as process events or doors opening and closing.

Your odour control systems must be effective, well maintained and monitored to ensure they are consistently performing as intended under the full range of normal operating conditions. In some cases, this will require continuous monitoring of relevant parameters and automated controls.

Your OMP must include all appropriate engineering assessments and monitoring plans.

Demonstrated effectiveness compared to accepted good practice

You will not be required to use effectiveness monitoring for odour control measures which are obvious and based on good principles. This includes measures such as:
- housekeeping
- thorough inventory controls for odorous waste
These methods are logical and widely accepted as appropriate measures, but demonstrating their effectiveness in particular situations can be difficult. You will still need to show you are using those controls to an appropriate standard.

The effectiveness of indoor air treatments, such as misting or reactive chemicals like ozone, are also very difficult to monitor. The Environment Agency will not accept these abatement solutions as appropriate measures until:
- they are more firmly established
- they have shown their effectiveness in a thorough assessment which is relevant to your activity
You must directly assess odorous emissions from stacks, vents or surfaces (such as open biofilters).

You must use an emissions monitoring contractor who is certified under the Monitoring Certification Scheme (MCERTS) to measure flow rates, take samples, and have them analysed by an accredited laboratory. They do this in line with BS EN 13725:2022, Stationary source emissions - Determination of odour concentration by dynamic olfactometry and odour emission rate. You must make provisions for representative sampling of air before and after treatment to allow this. Check the guidance on monitoring emissions to air, land and water (MCERTS) (https://www.gov.uk/government/collections/monitoring-emissions-to-air-land-and-water-mcerts).

Where processes and their emissions have been well characterised, it may be possible to confirm the ongoing effectiveness of odour controls by monitoring surrogate chemicals or parameters. This approach is only appropriate when:
- the monitoring method is sufficiently accurate
- the results have been shown to be an effective representation of odorous emissions
When surrogate methods require sampling and air flow rate assessments, you must still use MCERTS accredited stack monitoring contractors.

You must carry out emissions assessments at least once a year. This is so you can show that the abatement method is performing to a suitable standard, as specified in the permit application or OMP. To show ongoing performance, you must complete these assessments:
- before any maintenance
- under reasonable worst case loading conditions
While important, these assessments will not provide assurance that abatement systems are working as intended between sampling events. As such, you should have a system of frequent or, where practical, continuous monitoring of relevant secondary parameters. For example:
- daily visual inspections of a biofilter to look for dry areas
- continuous monitoring of parameters such as temperature, pressure and air humidity
- possible combination of both
Enhanced dispersion

Dispersion is a natural process where air pollutants mix with ambient air and become less concentrated. Weather conditions and distance from the source are major factors. This dispersion gradually reduces the perceived intensity and associated offensiveness of odorous emissions.

Enhanced dispersion methods fall into 2 general categories.
- Turbulent mixing uses physical barriers, such as a row of trees, to encourage mixing to achieve higher levels of dispersion over shorter distances.
- Elevated stacks aim to release odorous emissions high enough for them to be diluted below levels of concern before the stack plume disperses down to ground level. Ejecting emissions vertically at high speed may also help.
You can use modelling to assess the relative benefits of different enhanced dispersion methods.

Poor dispersion conditions

Odorous emissions may happen during business hours when you disturb or manage materials. These activities, such as turning composting windrows, must often be done on a schedule to maintain the process under control.

However, you should not carry out occasional activities such as clearing old waste stockpiles when there are poor dispersion conditions.

Poor dispersion conditions might include:
- wind speeds below about 4 metres per second (9 miles per hour)
- wind directions which are clearly toward a nearby sensitive receptor (https://www.gov.uk/guidance/risk-assessments-for-your-environmental-permit#identify-receptors)
A properly located local weather station can help you assess poor dispersion conditions.

If you have to carry out odorous activities during poor dispersion conditions, you must thoroughly evaluate and use additional measures for reducing odorous emissions when possible.

Location

The distance of sensitive receptors from your site is an important factor for odour pollution risks. You should select site locations a suitable distance from sensitive receptors whenever possible. Sites with sensitive receptors close to their boundaries will usually require stricter emissions controls.

If your site is very close to receptors, you should consider the layout of the site in relation to them. Moving odorous materials or processes to the opposite side of a large site can help with dispersion and reduce odour impacts from localised sources.

Novel methods

The Environment Agency is keen to hear about new technologies and ideas for reducing odorous emissions as part of permit applications. However, you need to provide evidence so they can consider if these technologies are an effective means of control.

You should:
- provide a clear explanation for how the technology works and intended applications
- provide evidence to show it works in practice for the intended applications
- quantify abatement performance standards where appropriate
- show the proposed method of applying the technology offers a plausible way of allowing its proposed benefits to be delivered in practice
You should show the new technology can handle either the:
- volume of air, its characteristics, humidity, contaminants, temperature and variability (frequency and duration)
- solid and liquid materials to be treated
You should also:
- provide details of the management and monitoring to ensure that the technology keeps working
- explain how it will be maintained
- consider what could go wrong and how pollution could be minimised should there be a failure
The Environment Agency will consider relevant evidence from:
- existing scientific literature or reports
- well-designed, documented and executed trials at relevant scale
Technology trials need to include:
- a comparison between the new technology and a control case
- information on the variation between measurements – this needs to show that the results are repeatable and not due to chance or noise in the data
- controls to show that the new technology is responsible for any difference in odour concentrations rather than a change in some other factors (such as time of year, type of waste or process controls)
Any technology trial report or existing study must include full details of how the work was carried out as well as the final data and results. For example, the Environment Agency needs to know:
- that the conditions were representative of ‘real-life’ and reasonable worst case operating conditions
- what temperature, humidity and ventilation rate were used
- if all the data are reported or whether some have been left out (if so, why)
The Environment Agency would also need to know details about the monitoring equipment. For example:
- what monitoring equipment was used
- if it was sufficiently sensitive and properly calibrated
- any relevant MCERTS accreditation
- where was it positioned – if the measurements were representative of what was happening everywhere or were influenced by local factors (more than one sensor may be required)
Before starting a trial, you should consider the risks and consequences of potential failures, with procedures put in place to minimise any pollution. Trials should have a defined start and end date.

You may need approval from us before conducting a trial. Follow the guidance on waste operations and A1 installations: carrying out research or trials (https://www.gov.uk/guidance/waste-operations-and-a1-installations-carrying-out-research-or-trials).

If you breach the odour condition while carrying out a trial, you may face enforcement action.

Some ambient air abatement systems (such as misting or ozone) attempt to treat indoor air directly. However, these have minimal potential for odour mitigation because of:
- a lack of control over mixing and dosage rates
- the relevance of chemical reactions and other abatement conditions
This approach can also lead to workers being exposed to harmful chemical reagents or other problems, such as limited visibility, associated with poor ventilation.

The Environment Agency may charge for new technology reviews in line with its charges guidance (https://www.gov.uk/guidance/environment-agency-fees-and-charges).

Minimising community impact

You need to understand the surrounding community to minimise the impacts of odour pollution.

You need to consider:
- what activities people are engaged in and how this influences their sensitivity
- what the pattern of these activities is over time
- how odours from the site affect exposed community members and what concerns they raise
- how the tolerance of the community towards odour pollution is affected by wider feelings about the operator, the site or the activity
Information about the surrounding community may help you make changes to site operations to minimise odour pollution and will be only one aspect of appropriate measures. For example, it might be an appropriate measure to avoid moving old materials, which could cause significant odorous emissions, during a local community event.

Go to the next section: 4. Assessing odorous emissions (https://www.gov.uk/guidance/odour-management-comply-with-your-environment-permit/4-assessing-odorous-emissions).

Or go back to contents (https://www.gov.uk/guidance/odour-management-comply-with-your-environment-permit).