Duncan Mounsor, sales and marketing director at Enviro Technology, explains how best to achieve continuous emissions monitoring systems (CEMS) best practice        

For many processing industry managers, ensuring that CEMS meet the required standards is a real headache – both in terms of time and money. The complexity doesn’t stop once a system is installed either. Striving to achieve stringent data capture rates and guaranteed system availability requirements (associated with the Large Combustion Plant Directive and Waste Incineration Directive for instance) is an ongoing journey, and requires dedicated management and maintenance of the technology.

In general, when purchasing CEMS, senior management still base their decisions on a two tier approach involving price and specification. Clearly, these two factors are important. However, a more sophisticated approach to the initial planning of projects can reap dividends. A consideration of installation needs encompassing calibration as well as ongoing service and maintenance, can make a significant difference when living and working with CEMS over their expected ten year plus lifecycle.

Best practice dictates that a third tier should be included in the decision making process, looking closely at the specific needs of individual CEMS installations. Factors to consider include how much intervention is likely to be needed during the technology’s lifetime, how challenging it will be to perform this intervention and how the total cost of ownership can be reduced.


Legal requirements surrounding the measurement of stationary source emissions are set and controlled by the Environment Agency. Full guidelines are detailed in BS EN 15259, including requirements for measurement sections and sites, as well as for measurement objectives, plans and reports.

The section of BS EN 15259 that most influences the suggested ‘third tier’ to decision making is, ‘procedure for planning a CEMS location’. Shrewd interpretation of this part of the standard can enable plant managers to improve efficiency and cut costs, whilst completely satisfying all legal obligations.

The main objective of this part of the Environment Agency’s guideline is to ensure that samples for CEMS analysis are analogous to the final emission that leaves the stack and enters the atmosphere. So, the assumption is usually made that the system needs to be located as close as possible to the top of the stack to ensure the emission is a well mixed, representative sample.

For many plants, this causes a real problem. For a start, it sometimes requires the design, fabrication and erection of dedicated access platforms to support and hold the system – which can come at a high price. And, when a system is 30 metres up in the air, only accessible via a ladder, conducting routine maintenance is no mean feat. Even the most basic tasks like cleaning the windows on a low maintenance OPSIS cross-duct CEM system, can require planning and specialist equipment.

For many sites, this results in a catch-22 situation during poor weather conditions. What do you do if health and safety guidelines state that it is not acceptable for someone to ascend the platform in windy conditions, but you know that your CEMS requires a quick tune-up in order to meet its data capture requirements?

An alternative

With an in-depth understanding of industry emissions, and of the grounds for the BS EN 15259 guidelines, it is possible to reinterpret the requirements.

For instance, when an emission is gaseous rather than particulate matter, the rationale behind taking a sample from the top of the stack becomes redundant, especially if gas turbine engines are used. The gas will be extremely well mixed before it reaches the final point of emission, so it is perfectly acceptable to position the CEMS closer to ground level in a location that is convenient for ongoing management and maintenance.

As the industry regulator, the Environment Agency gets the last say as to where CEMS are located. So a strong case needs to be made for choosing a more practical position.

One large industrial process operator that Enviro Technology advised on reinterpreting the rules, appointed a third party testing company to prove that it was just as effective, and accurate, to monitor emissions at ground level as it would be at the top of its stacks. The verification process involved using a third party, MCERTS accredited stack testing team to measure emissions across the stacks at different locations and heights.The aim was to check that the gas was homogenous and ensure that the Environment Agency was satisfied with the report detailing the proposed ground level location of the CEMS.

This activity saved an estimated £1m which would have been required for structural platforms to house the CEMS at eight stack top locations. Not to mention the substantial man hours that would have been lost due to plant operators ascending the platforms for maintenance.

Having the CEMS equipment at ground level eliminated many possible operational problems. It also reduced the risk of potentially large fines or enforced plant shutdown if maintenance issues had led to the monitoring technology not delivering the required data availability and up-time.

It is common knowledge in the industrial emissions industry that equipment that is easy to maintain will be maintained. When it comes to CEMS, it is vital to have the knowledge, insight and courage to intelligently question the guidelines. It is not always necessary to take them at face value. If you can suggest appropriate, compliant alternatives that save time and money and satisfy the Environment Agency, everyone is a winner.

Enviro Technology


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