Dust
Acceptable Levels
The phrase "acceptable levels" can be quite a controversial term, in that what is deemed acceptable to one person may not be thought of as acceptable by another. In this context, the term "acceptable level" of dust is used in reference to widely established practice or standards.
A number of separate ambient air quality and emission standards exist, based on the maximum impact allowed before harm is likely or nuisance is perceived. There can however, be conflict between these two strategies as an emission standard may allow for a particular level of dust emission that exceeds an air quality standard. An air quality standard will allow for all source contribution, both natural and anthropogenic. Therefore, a mineral extraction process will add to the existing "background" dust levels and requires assessment as to what the level of contribution is. This will require prediction of the dust emission prior to development approval, and monitoring (and discriminating between) both the "background" and actual dust emissions during site operations.
Statutory air quality data for suspended particulate matter exist in the UK (Table 8 457). However their applicability to mineral dusts is questionable as they were originally developed for airborne combustion by-products. No such statutory limits for nuisance dust exist for the UK.
Table 8. Air Quality Standards for Total Suspended Particulates.
| Authority | Pollutant | Objective | Measured as: | Relevance |
| EC/UK Air Quality Standard | PM10 | 50 μg/m3. Exceeded < 35 times/annum | 24 hr mean | Air quality in relation to public health |
| 40 μg/m3 | Annual mean | |||
| Scotland | PM10 | 50 μg/m3. Exceeded < 7 times/annum | 24 hr mean | |
| 18 μg/m3 | Annual mean | |||
| UK Air Quality Standard (Provisional) | PM2.5 | 25 μg/m3 | Annual mean | Possibly incorporated by mid-2011 |
| UK occupational exposure limit | Total inhalable fraction | 10 μg/m3/day | Ave. over 8 hr period | Occupational exposure (health) |
| USA National Ambient Air Quality Standard | PM10 | 150 μg/m3 | 24 hr mean | Air quality in relation to public health |
The public response to what constitutes "nuisance" (Table 9) is reported by several authors 70 71 72 73 in respect of background and additional fugitive deposited dust levels, based on the various units of soiling.
Table 9. Public response levels related to deposition rates.
| Public Response | Typical Situation | Measure of soiling | |
| % EAC/day | mg/m3day equivalent* | ||
| Rural | 0.01 | 2.38 | |
| Suburban/small town | 0.02 | 4.76 | |
| Noticeable | 0.2 | 47.6 | |
| Urban | 0.3 - 0.4 | 71.5 - 95.3 | |
| Possible complaint | Rural summer time | 0.5 | 119.1 |
| Objectionable | 0.7 | 166.8 | |
| Industrial | 0.8 - 1.0 | 190.6 - 238.2 | |
| Probable complaint | 2.0 | 476.4 | |
| Serious complaint | 5 | 1191.1 | |
| *Based on conversion after Beaman and Kingsbury. 74 | |||
The limit of nuisance dust customarily accepted in the UK is given in Table 10, together with standards and guidance from other countries for comparison.
Table 10. Guidelines and Standards for Nuisance Dust Deposition.
| Authority | Pollutant | Objective | Measured as: | Relevance |
| Nuisance: mass deposition measurements | ||||
| UK 'unofficial' nuisance dust deposition rate 75 | All particulates | 200 mg/m2/day | Annual mean | Serious nuisance |
| West Australia Nuisance Standard | All particulates | 133 mg/m2/day | Monthly mean | First loss of amenity |
| 333 mg/m2/day | Unacceptable reduction in air quality | |||
| West Germany Nuisance Standard | All particulates | 350 mg/m2/day | Monthly mean | Possible nuisance |
| 650 mg/m2/day | Very likely nuisance | |||
| Malaysia Air Quality Standard | All particulates | 133 mg/m2/day | Nuisance dust deposition | |
| Nuisance: soiling rate measurements | ||||
| UK glass slide guideline 76 | All particulates | 20 - 25 soiling units/week | Mean of four 1 week samples | Upper limit of acceptability through soiling |
The wide range of values and subjective descriptions used to define "acceptable" nuisance dust deposition or soiling, together with the fact that complaints are often received well below these levels, demonstrates the urgent requirement for an empirical standard to be adopted, based on the central feature of nuisance dust, i.e. as a visible effect. This should be differentiated from the important, but unrelated, monitoring of health-related particulates as the airborne concentration of a size-related fraction.
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