Construction dust risk assessment to the IAQM method
A site can be high risk for trackout and low risk for construction. Scoring the four activities separately is what the method is for.
A construction dust risk assessment scores four activities separately rather than treating a building site as one source. Demolition, earthworks, construction and trackout each get their own emission magnitude, each is combined with the sensitivity of the surrounding area, and each ends up with its own risk category. A site can be high risk for trackout and low risk for construction, and the mitigation follows accordingly.
That structure comes from the Institute of Air Quality Management's guidance on dust from demolition and construction, which is what almost every local authority in England now expects to see applied. Check which version is current before you start, because the thresholds have been revised.
The four activity types and why they are scored separately
Demolition covers taking structures down, including on-site crushing and screening. Earthworks covers stripping, excavation, levelling, stockpiling and bund formation. Construction covers the building works themselves, including cutting, concrete batching and any abrasive processes. Trackout covers material carried onto the public highway by vehicles leaving the site.
Keeping them apart matters because they happen at different times, affect different receptors and need different controls. Damping down an excavation does nothing about mud on the road, and a wheel wash does nothing about cutting dust on the eighth floor.
It also matters for programming. A site with a short demolition phase and a long construction phase carries its highest risk for a few weeks, and the assessment should say so rather than implying a year of high risk.
Screening: does an assessment apply at all
The first step asks whether there are receptors close enough to matter. The guidance screens in a site where human receptors lie within 350 m of the site boundary, or within 50 m of the routes used by construction vehicles on the public highway up to 500 m from the site entrance. Ecological receptors are screened at 50 m from the boundary and from those routes.
Most urban sites screen in immediately. Isolated rural sites do not, and where that is the case the assessment can be short: state the screening result, identify the nearest receptors with distances, and stop.
Measure the distances properly and put them in a table. Officers check them.
Dust emission magnitude and how it is judged
Each activity is classified as large, medium or small using physical thresholds. The figures below reflect the widely used version of the guidance, and they should be verified against the edition current when you write.
| Activity | Large | Medium | Small |
|---|---|---|---|
| Demolition | Building volume above 50,000 m3, or work above 20 m | 20,000 to 50,000 m3, or work 10 to 20 m above ground | Below 20,000 m3, low dust potential materials |
| Earthworks | Site area above 10,000 m2, dusty soils, bunds above 8 m | 2,500 to 10,000 m2, moderately dusty soils | Below 2,500 m2, coarse grained soils |
| Construction | Building volume above 100,000 m3, on site concrete batching | 25,000 to 100,000 m3, dusty materials | Below 25,000 m3, low dust potential materials |
| Trackout | More than 50 heavy vehicle movements a day, unpaved route above 100 m | 10 to 50 movements a day, unpaved route 50 to 100 m | Fewer than 10 movements, unpaved route below 50 m |
Where a site sits between categories, say which criterion drove the classification. Assessments that assert a magnitude without showing the input are the ones environmental health officers query first, and the query costs more time than the working would have taken.
Sensitivity of the surrounding area
Sensitivity is assessed separately for three effects: dust soiling of property and surfaces, human health effects from particulate matter, and effects on ecological receptors.
For soiling and health, the inputs are the sensitivity of the receptors, how many there are and how far away. Residential property is high sensitivity for soiling; offices and retail are lower. For health, the annual mean background concentration of particulate matter also feeds in, taken from the national background maps for the relevant grid square, which means a site in an area with elevated background concentrations reaches a higher sensitivity band than an identical site elsewhere.
Ecological sensitivity depends on the designation and on how dust sensitive the habitat is. A site next to a statutory designation with dust sensitive vegetation needs the ecology strand taken seriously rather than dismissed in a sentence.
Combining the two into a risk category
Emission magnitude and area sensitivity are combined in matrices to give a risk of negligible, low, medium or high for each activity and each effect. The output is a grid, and the grid belongs in the report in full.
Two points are worth making about how the result is read. The risk category describes the risk before mitigation, which is what the guidance intends, so a high risk finding is not a problem to be argued away. And the overall conclusion, once mitigation appropriate to the highest risk category is applied, is normally that residual effects are not material. That is the expected outcome, and an assessment reaching it with the working shown is far more persuasive than one that manufactures a low risk by understating the magnitude.
Where wider operational air quality effects also arise, they belong in a separate Air Quality Assessment chapter rather than being folded into the dust risk.
Mitigation tied to the risk category
The guidance provides measure sets by risk category, and the discipline is to take the measures for the highest category any activity reaches, then add the activity specific ones.
Typical medium and high risk measures include a named site manager responsible for air quality, a complaints log with a published contact, damping down of haul routes and stockpiles with a recorded regime, sheeting of loads, wheel washing and a hard surfaced route to the site exit, road sweeping on a defined frequency, enclosure or damping of cutting and grinding, no bonfires, and restrictions on drop heights when loading.
Plant emissions sit alongside dust. In London, non-road mobile machinery has to meet emission standards set by the Greater London Authority within defined zones, with plant registered before use, and other authorities increasingly apply similar conditions.
Monitoring and trigger levels
High risk sites usually need monitoring. The options run from daily visual inspections recorded in a log, through dust deposition or directional gauges, to real time particulate monitors at the boundary with alert thresholds.
Real time monitoring only helps if someone acts on it. Set the trigger level, say who receives the alert, and state what happens: stop the activity, increase damping, review the following day. A monitoring condition without a response protocol produces data and nothing else.
The whole package belongs in the construction management plan, alongside the noise controls and any section 61 consent for construction noise and the vibration controls for piling or breaking. Authorities increasingly condition a single construction environmental management plan covering all of it, which is easier to enforce and easier to comply with than three separate documents.
For specialist technical reports, qualified professional input may be required, and a dust assessment on a large or sensitive site is one of them. This is general guidance, not legal advice. Check the position with your local planning authority before relying on it.
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Frequently asked questions
Which four activities does the assessment score?
Demolition, earthworks, construction and trackout. Each receives its own dust emission magnitude, is combined with the sensitivity of the surrounding area, and produces its own risk category. They happen at different times, affect different receptors and need different controls, which is why they are not combined into a single site score.
What are the screening distances?
Human receptors within 350 m of the site boundary, or within 50 m of the routes used by construction vehicles on the public highway up to 500 m from the site entrance. Ecological receptors are screened at 50 m from the boundary and from those routes. Most urban sites screen in immediately and need the full assessment.
Does a high risk category mean the scheme is unacceptable?
No. The risk category describes the position before mitigation, which is what the method intends. Once measures appropriate to the highest risk category are applied, the usual conclusion is that residual effects are not material. An honest high risk finding with proper mitigation reads better than an understated magnitude.
How does background pollution affect the result?
It feeds into the sensitivity of the area for human health effects. The annual mean background particulate concentration for the relevant grid square is taken from the national background maps, so an identical site in an area with elevated background concentrations lands in a higher sensitivity band than one in a cleaner area.
What monitoring is expected on a high risk site?
It ranges from recorded daily visual inspections to dust deposition or directional gauges and real time particulate monitors at the boundary. Whatever is used, set the trigger level, say who receives the alert and state the response. Monitoring without a defined response protocol produces data and no protection.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.