What's the logic in adding DBFs to machines over 37kW?

The London Best Practice Guide requires diesel particulate filters to be retrofitted to machines over 37kW on construction sites such as the Olympics. Is this sensible?

The debate raging about the merits or otherwise of retrofitting diesel particulate filters (DPFs) to plant is not purely a concern for those bidding to supply kit to the Olympics, the Thames Gateway and the DLR extension. But the requirement, contained in the London Best Practice Guide (BPG), could be coming to a site near you if the Environmental Industries Commi-ssion (EIC) has its way.

The EIC says poor air quality reduces life expectancy of every person in the UK by an average of seven or eight months and impacts particularly on children, the elderly and those in poor health. It has lobbied transport minister Jim Fitzpatrick to recommend the BPG to city councils across the UK facing difficulties in meeting air quality standards. It persuaded 28 MPs to sign an Early Day Motion calling on the Olympics Delivery Authority (ODA) to adopt the BPG - which the ODA has confirmed it will do.

Danny Stevens, public affairs manager at the EIC, says: "Dust and emissions from demolition and construction sites have a significant impact on poor air quality, not only on the site itself, but also on the health of people living and working in the surrounding area. The BPG sets out a sensible approach for major construction sites to take a lead in showing social responsibility by reducing pollution from the equipment used on those sites.

"It's hard to see how anyone can argue against such measures."

However, many people do. First up is Tim Faithfull of the CEA, which represents plant manufacturers.

He says retrofitting a DPF could cause problems with warranty cover for the engine and the machine in general. He is particularly concerned that the exhaust after-treatment could be a burn hazard or create a blind spot by blocking the operator's view.

Stage IIIB regulations

Furthermore, Faithfull points out that Stage IIIB emissions regulations start to come into force at the beginning of 2011. This reduces the allowable particulate emissions by 90% over Stage II to the equivalent of a machine fitted with a DPF. All engine and plant manufacturers are working on properly engineered and tested solutions in readiness for this legislation.

Construction Plant-hire Association (CPA) chief executive Colin Wood has long campaigned against the need to retrofit DPFs. He points out that the EIC's title is something of a misnomer, as in reality it is an association representing emission abatement suppliers, including DPF manufacturers.

Stevens says: "We would urge organisations such as the CPA to stop campaigning against clean air and to encourage its members to recognise they must play their part in a responsible construction sector by tackling the pollution their equipment produces."

However, Wood counters: "The reason they always try to take the moral high ground is because the research and the facts simply don't support their arguments, or attempts to drum up business for their members."

So what are the facts?

There is no question that poor air quality is detrimental to health - the Great Smog in London in 1952 is estimated to have lead directly to 4,000 deaths, followed by twice that number over the following months.

Particulates are miniscule specks of matter so small they can be drawn deep into the lungs. They are classified by size as measured in microns (one millionth of a metre or one thousandth of a millimetre). So PM10s are all particles up to one hundredth of a millimetre (0.01mm), or about a seventh the thicknesses of a human hair.

There are many natural forms of particulate (dust, sea salt and so on) but in relation to engines, they are formed of partially burnt fuel and oil expelled in the exhaust gas.

For legislative purposes, particulates are weighed and not counted or differentiated as to their source. In the UK the limit for PM10s is 50 micrograms per cubic meter of air (μg/m3) averaged over 24 hours. To put this figure in context, cigarette smoke has a particulate level of around 720,000μg/m3 - some 14,000 time higher than the allowable pollution level in the UK. A Canadian study found particulate concentration in office buildings' smoking areas ranged from 30μg/m3 to 100μg/m3.

Local authorities and councils are responsible for air quality and can be fined if the limit is exceeded more than seven times per year (or 10 to 14 times a year in London).

EU figures show the biggest particulate producers are combustion plants, road transport, production facilities and energy generation. A technical review published last year by the EU found that construction plant currently accounts for 1.6% of the total PM10 emissions in the atmosphere and this will fall by 2010 and again by 2015.

DPFs are extremely efficient in capturing particulates and have been used for some time on machines working in confined spaces such as tunnels and on plant operating in Switzerland. By the end of 2010 the EU's Stage IIIB emissions regulations mean DPFs will probably be standard equipment.

Plant owners forced to retrofit DPFs are likely to select older warranty-expired machines conforming to the EU's Stage II regulations, which allows 40% more NOx (nitrogen oxide and nitrogen dioxide) emissions than Stage IIIA. NOx spreads more easily over larger areas than particulates and contributes to photochemical smog. DPFs have virtually no effect in reducing NOx emissions - indeed two years ago it was found the units fitted to London's buses actually increased NO2 emissions by a factor of five.

Under the BPG, filter manufacturers have to register their company and products with the Energy Savings Trust (EST) at an annual cost of £2,000 for the company and £2,000 for each filter type. Retrofitting a DPF to a machine will cost between £2,000 and £6,000 (and possibly more). Komatsu offers a factory-fit DPF system on some excavators, which adds almost £6,000 to the cost of the machine, but this is not registered with the EST.

On site

The Greater London Authority commissioned an 18-month study of emissions from a building site (approximately 40m x 25m) where one building was demolished and another constructed.

The report said: "The results indicated that there were some increases in the background ambient concentrations of PM10 particles in the order of 2μg/m3 to 10μg/m3 at the site boundary." It goes on to say: "At distances greater than approximately 130m, the direct influence of PM10 emissions from the construction site could not be readily identified above the local background concentration. This has potential implications for site operators, planners and air quality regulators, as it shows the approximate range over which a proposed construction site could influence local air quality."

The 50μg/m3 daily limit was exceeded six times during the study period - five of which coincided with high levels of background pollution. One was due to 'bonfire night' celebrations, which saw pollution hit an hourly peak of more than 500μg/m3.

The highest pollution level due to the building works occurred during demolition of a building close to the on-site monitoring station, which recorded an hourly peak of 480μg/m3 but did not breach the daily limit. Levels were much lower the following day after switching from fixed to hand-held water suppression reduced the demolition dust. At two remote monitoring stations, around 150m from the site and almost diametrically opposite, recorded levels were between 16μg/m3 and 22μg/m3.

Only when a diesel-fuelled powerpack was positioned 5m from the monitoring station during auger piling operations did exhaust emissions feature in the statistics. This pushed the hourly average to a peak of 70μg/m3, although over the week the average during the working day was only 21μg/m3, with background levels of 13μg/m3 and 14μg/m3 at the remote stations.

So what next?

The BPG lays down some sensible guidelines to reduce air pollution from construction sites, but the requirement to retrofit DPFs has no meaningful scientific foundation. Particulate contribution from construction machinery is very low and will get even smaller from 2010 onwards.

On the Olympics site, the bill to retrofit DPFs could hit £9m, with no substantial benefit to those on, or surrounding, the site. That money would be better spent tackling other particulate sources - permanently benefiting thousands, potentially millions, of people across the country, rather than the few working on or living adjacent to a handful of temporary construction sites in London.

DPFs on the Olympic site - the cost and benefits

• With 2,000 machines expected to be working on the Olympic site, the cost of retrofitting DPFs to those over 37kW (say 1,500 units) would be a minimum of £3m - but could hit £9m.
• Up to 22,000 people will work on the 246ha Olympics site and there are very few houses within 130m of the boundary. Standard working practices should keep most workers more than 5m away from large working machines and any such exposure is likely to be brief and intermittent.
• Site workers are not in the vulnerable groups identified by the EIC and unlikely to suffer from a small, temporary rise in particulate concentration.