IAQM construction dust risk categories and mitigation

A construction dust assessment under the IAQM method does not produce a concentration or a modelled contour. It produces a risk category for each of four activities, and that category decides the length of the mitigation schedule. Get the categorisation right and the mitigation follows almost mechanically. Get it wrong, and you either over-commit to measures the site cannot sustain or under-commit and attract a condition you cannot discharge.

The four activities are demolition, earthworks, construction and trackout. Each is scored separately, because a site can be a high risk for trackout along an unpaved haul road and a negligible risk for demolition.

Why a dust assessment is asked for

Dust is a local amenity and health question rather than a national compliance one. Planning practice guidance expects air quality effects to be considered where development could be affected by poor air quality or could itself make it worse, and most local validation lists translate that into a requirement for a dust assessment where demolition or significant earthworks are proposed near people.

Screening comes first. The IAQM approach asks whether there are human receptors within a stated distance of the site boundary, and within a stated distance of the routes construction vehicles will use on the public highway for a defined distance from the site entrance, with tighter distances for ecological receptors. The published screening distances in the guidance are 350m from the boundary for human receptors and 50m from the vehicle route up to 500m from the site entrance, with 50m used for ecological receptors. Check the current version of the guidance, because the document has been revised and the detail moves.

If nothing screens in, say so in one page with the distances measured and a receptor plan. That short document saves a consultation round.

The four activities and how each is scored

Each activity gets a dust emission magnitude of large, medium or small. The driver differs by activity, which is the part applicants most often get wrong by applying a single site-wide judgement.

The published thresholds in the guidance are expressed in round numbers, for example a large magnitude for demolition at building volumes above 50,000m³, for earthworks at site areas above 10,000m², for construction at total building volumes above 100,000m³, and for trackout at more than 50 heavy duty vehicle outward movements a day. Verify them against the version your local authority is working to, since the categories have been refined since the original publication.

Two practical points. Demolition magnitude depends on volume, not footprint, so a tall narrow building scores higher than a wide single storey one of the same area. And trackout is where small sites generate large scores, because a 20 house scheme on a farm access can easily exceed the movement threshold while every other activity sits at small.

Sensitivity of the surrounding area

The second axis combines how sensitive the receptors are with how many there are and how close. Residential property, schools and hospitals are treated as high sensitivity for dust soiling and health. Offices and retail are lower. Designated ecological sites with dust-sensitive habitats are assessed separately.

Numbers and distance then modify the result. A single dwelling at 300m produces a different sensitivity to twenty dwellings at 20m. The output is a sensitivity of the area of low, medium or high, assessed for three separate effects: dust soiling, human health through PM10, and ecological.

Where the site falls inside an air quality management area, the existing background matters to the health axis and the authority will expect it addressed explicitly. The interaction with wider restrictions is covered in our note on clean air zones and what they mean for a development.

Get the receptor plan right and the rest of the assessment is arithmetic. Most disagreements with environmental health officers are disagreements about the receptor plan, not about the method.

Risk categories and the mitigation that follows

Magnitude and area sensitivity combine in a matrix to give a risk category for each activity and each effect: negligible, low, medium or high. The highest category across the activities sets the site-wide mitigation package, and the guidance distinguishes between measures that are highly recommended and those that are desirable at each level.

The mitigation falls into groups that should appear as headed sections in the submission:

• Site management, including a named responsible person, a dust log and a complaints procedure.
• Monitoring, scaled to the risk category.
• Preparing and maintaining the site, covering hoarding, screening, surfacing and stockpile management.
• Operating vehicles and machinery, covering engine idling, speed limits on unpaved surfaces and plant emission standards.
• Operations, covering water suppression, enclosure of dusty activities, cutting and grinding controls and drop heights.
• Waste management, with no burning on site.
• Measures specific to demolition, earthworks, construction and trackout, including wheel washing and road sweeping.

A medium risk site with a short, specific schedule under those headings discharges more easily than a low risk site with a 40 page generic document. Officers read for the site-specific measures and skip the boilerplate.

Monitoring, trigger levels and action

Monitoring is where applicants over-promise. Three approaches exist and they answer different questions.

Visual inspection, carried out daily and recorded, catches most problems and costs almost nothing. Deposition and soiling measurement, using deposition gauges or sticky pads, gives a record of nuisance over weeks and is useful for defending against a complaint. Real-time PM10 monitoring with alarms gives immediate feedback and is the only method that supports an action trigger during a shift.

There is no national trigger level for construction dust. Any figure in a management plan is a site-specific threshold agreed with the authority, and it has to be tied to an action rather than to a report. The useful drafting states the measured parameter, the threshold, who is alerted, what stops, and within what period. A trigger with no stated response is decoration.

Record the dust log honestly, including the days work was modified because of wind direction. A contemporaneous log that shows the site responding is worth considerably more in a nuisance complaint than a clean log nobody believes.

What goes in the construction management plan

Dust rarely gets its own condition. It usually arrives inside a construction management plan condition alongside traffic routeing, hours, wheel washing, noise and vibration, so the dust content needs to be identifiable within it.

Include the risk categorisation and its date, the receptor plan, the mitigation schedule keyed to the risk category, the monitoring regime with locations shown on a plan, the trigger and response table, the named responsible person with a contact number, and the complaints procedure with response times. Where plant noise and generator testing also feature, the assessment overlaps with the work described in standby generator testing and the noise it creates, and the same management plan can carry both.

Keep the construction programme consistent with the assessment. A plan that assumes sequential demolition and earthworks, submitted with a programme showing them running together, invites a request for a revised assessment.

Discharging the condition

Submit early, ideally with the application rather than after grant, because dust conditions are frequently drafted to be discharged before works begin and a late submission stops the site.

A clean discharge submission has four parts: the dust assessment with its risk categories, the management plan, the monitoring plan with locations, and a short covering note that maps each requirement in the condition wording to a page in the submission. That mapping note is the single most effective thing you can add, since it removes the officer's reading burden.

Where the wider air quality position also needs addressing, for example because the development introduces new combustion plant or changes traffic flows, that belongs in an Air Quality Assessment rather than in the dust chapter. Councils normally expect that work from a suitably qualified author and professional review of any draft is strongly advised. Where construction noise is a parallel concern, a Noise Impact Assessment covers the ground the dust assessment does not.

And if the site layout changes after approval, revisit the trackout score. It is the one category that moves when a site entrance moves.

Enter your postcode on PlanScope to see which air quality and construction stage reports your site is likely to need.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.