Clearing the air
June 1st 2007

One of the main legal requirements applying to construction sites are the provisions of the Health and Safety at Work Act 1974. Under the Control of Substances Hazardous to Health (COSHH) Regulations 2002, developers must ensure that they take into account risks to the workforce from exposure to any harmful substances generated by work activities including: very toxic, toxic, harmful, corrosive or irritant substances.

Some of the most hazardous dust types generated on construction sites are asbestos, crystalline silica and wood dust. Other particulates may include, welding fumes, chemicals and paint fumes and moulds, among others. For sites with potentially asbestos-containing materials, a separate method statement will need to be produced by a specialist asbestos treatment contractor, and air samples must be analysed off site by specialists.

In most cases, when it is reasonable to expect dust levels to be significant, effective dust and emission control measures should be in place for every dust generating activity carried out on site, not only to protect the health and safety of the on-site workforce, but also members of the public in the locality.

In order to measure the effects, a sampling regime for personal and ambient dust levels needs to be established, then appropriate control measures can be introduced to keep the levels below the required levels.

There are also many environmental conditions and controls now imposed on construction sites, to monitor the dusts which are being generated and may go over the site boundaries. Under Part III of the Environmental Protection Act (EPA) 1990, emissions of dust, fumes and other effluvia from construction sites can be identified as a statutory nuisance if prejudicial to health or a nuisance.

Monitoring For personal exposure monitoring, personal air sampling pumps are used. A sample is collected onto a filter media over an 8 hour exposure, and the filter can be sent away for gravimetric or chemical speciation (to determine the actual compounds attached to the particulate matter). The pumps are rugged and relatively unobtrusive, enabling work to carry on unheeded. For gases or chemical fumes of a non-particulate nature the same sampling method is used, but at very low flow rates, via absorption tubes of usually carbon or silica gel. These tubes are then sent to a laboratory for chemical analysis.

Real time In many instances, this method of detection will result in an indication of the total dust exposure over the duration.

In some instances it is beneficial to have an indication of the dust levels in real time, in order to highlight specific activities, for example; the use of grinding discs which may be contributing most to the overall dust loading.

Instruments such as the Microdust Pro, a real time light scattering device allows an operator to undertake a 'walk through' survey of the site, or monitor specific processes and then download the data for analysis.

Continuous site monitoring is still an important way of helping developers manage dust and PM10 emissions (particles with diameter less than or equal to a nominal 10µm) from construction and demolition. Various methodologies can be adopted, the simplest is a visual inspection. There is also simple gravimetric sampling, where volumes of air are drawn through a filter. This monitoring method is considered to be the most accurate and produces concentrations equivalent to the EU reference samplers, which are used to set EU limit values.

Real time dust monitors can be used in an enclosure and left at various sites around the boundary. The APM (airborne particulate monitor) is a permanent light scattering device with heating (to remove moisture effects) which can be accessed manually or if fitted with GSM (global system for mobile communications), allows data to be downloaded remotely for analysis and a profile of the site made. This data can also be reported to, or taken directly by the local council if required in order for them to directly police the sites activities.

There are also simple but accurate methods to measure nuisance dust and its composition. Dust is collected onto a horizontally mounted capture container or, in the case of a Directional Dust Gauge, into four vertical tubes aligned in different directions.

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