Environmental Monitoring Standards and Methods - Selection of standards for emission monitoring [Dec 2009]
With the increasing requirement for the installation of continuous emission monitoring systems (CEMS) it is important that capital investment is protected and that instrumentation gives reliable, meaningful and repeatable data. Fitting MCERTS-approved equipment is one element but it is extremely important that the system is verified. The verification process requires the use of standard reference methods to underpin the data.
Standard reference methods are essential for the effective measurement and control of air pollution. Such standards are developed at National, European and world-wide level. The robustness and fitness for purpose of these standards is a function of the accumulated expertise and experience of the people who work together in committee to produce them. Where internationally-derived standards are binding on the UK, as European (CEN) standards are, it is particularly important that they should recognise UK interests and sensitivities. BSI manages the UK input to new standards via its technical committees and the UK experts that they nominate to CEN and ISO working groups.
ISO standards are accepted on a case by case principle, it is not mandatory for a member country to adopt a standard.
CEN standards are mandatory and must be adopted by member states of the European Union. If a conflicting standard is in existence then this must be withdrawn.
BSI technical committee EH/2 is responsible for air quality issues. The sub group EH/2/1 is specifically charged with stationary source other BSI committees, reflects the widest possible range of users.
“the choice of the method is often dictated by the requirements of a relevant EU Directive”
Standards developed and published by CEN are generally accepted as being the most robust. However, other standards are still important, as there are substances that are not, as yet, covered by CEN Standards. The choice of the method is often dictated by the requirements of a relevant EU Directive, where, for example, the use of CEN standards is mandatory. If the standard is not dictated by mandatory requirements then monitoring standards should be used in the following order of priority as given in the European IPPC Bureau’s Reference Document on the General Principles of Monitoring:
• Comité European de Normalisation (CEN)
• International Standardisation Organisation (ISO)
If the substance cannot be monitored using standards covered by the above then a method can be selected from any one of the following:
• American Society for Testing and Materials (ASTM)
• Association Francaise de Normalisation (AFNOR)
• British Standards Institution (BSI)
• Deutsches Institute fur Normung (DIN)
• United States Environmental Protection Agency (US EPA)
• Verein Deustcher Ingenieure (VDI)
If the substance cannot be monitored using standards covered by the above then the following occupational methods may be developed, following the requirements of ISO 17025, for stackemission monitoring:
• Method for the Determination of Hazardous Substances (MDHS) series published by the Health and Safety Executive (HSE)
• National Institute of Occupational Safety and Health (NIOSH)
• Occupational Safety and Health Administration (OSHA)
The intended application of the standard method must always be taken into account; for example, a CEN method may be less suitable than another less-rigorously validated standard method if the application is not one for which the CEN method was developed. The Environment Agency produces, wherever required, Method Implementation Documents (MIDs) which detail the applicability of methods. The methods detailed in Environment Agency Technical Guidance Note (Monitoring) M2 ‘Monitoring of Stack Emissions to Air’ should be used unless it can be demonstrated that they are not fit for purpose for a particular application.
The importance of good sampling locations
Background
The Environment Agency(EA) established its Monitoring Certification Scheme (MCERTS) to deliver environmental measurements that meet their requirements for suitability and quality. MCERTS covers the product certification of monitoring systems, the competency certification of personnel, the accreditation of laboratories and the provision of third party inspection services. In Stack Emission Monitoring the importance of the location of equipment and sampling facilities is paramount.
Stack emission measurements require defined and stable flow conditions at the sample location. This allows the velocity and concentration of the measured component in the stack emission to be determined. If suitable sampling facilities are not available it will mean that sampling of pollutants cannot be done in compliance with the required sampling methods. This means that the uncertainty associated with the results is greatly increased. In these circumstances meaningful results from stack emissions monitoring cannot be achieved.
“defined and stable flow conditions at the sample location are essential to determine the velocity and concentration of the measured component”
Designing new plants
It is essential that designers of new plants remember to take account of stack emission monitoring at the plant’s design stage. Once a plant is built it is extremely difficult, if not impossible, to retrofit appropriate sampling facilities.
It is extremely frustrating for all concerned if the sampling location does not comply with the sampling requirements because it is either located in the wrong place or the sampling platforms are too small and do not allow access to the stack.
“it is essential that designers of new plants remember to take account of stack emission monitoring at the plant’s design stage”
In England and Wales Permit applications and Variations require the operator to assess the sampling arrangements against the requirements of Environment Agency Technical Guidance Note M1. It is essential that this process is carried out at the plant design stage. Once this has been done it is strongly recommended that advice and confirmation of the sampling arrangements is sort from the Environment Agency.
Installing a suitable sample location
The sample plane must be positioned such, that there are homogenous flow conditions, which allow representative samples of the stack gas emission to be taken. In summary, for newly built plant the sampling plane should be located according to the recommendations contained in Table 1.
Sampling facilities for gas concentrations
The location requirements for measuring gas concentrations are less exacting than for particulates, as variations in velocity profiles tend not to affect the homogeneity of the gas concentration. In practice, meeting the requirements for particulates will satisfy the requirements for gases.
“the location requirements for measuring gas concentrations are less exacting than for particulates, as variations in velocity profiles tend not to affect the homogeneity of the gas concentration”
Gas Detection Sampling facilities for CEMs
When designing a plant that requires CEMs to be installed, access and facilities are required to enable calibration by periodic monitoring, routine maintenance and functional checks to be done.
As CEMs require calibration by periodic monitoring the access and facilities should as a minimum comply with the requirements given for particulates and gases respectively.
Measurement ports
Measurement ports should be considered at the design stage of new plants, as installing ports after a plant is built may be difficult and costly (or impossible if protective linings are present). In summary the access ports:
• Must be big enough for the insertion and removal of the equipment used. It is recommended that access ports have a minimum diameter of 125mm, except on stacks smaller than 0.7m diameter. For small stacks a smaller port may be appropriate
• Must be installed at a suitable height to the platform, so that the equipment can be manoeuvred. A working height of approximately 1.2m to 1.5m is recommended
Sampling platforms
The sample location must be situated where it is possible to erect suitable working platforms. Ideally, the measurement site should be easily and safely accessible via stairs. Particulate and velocity based measurements require a sufficiently large working area around the stack along the measurement lines, so that the measurement points can be sampled with the appropriate length probes.
In summary:
• The platform surface area should not be less than 5m2
• The minimum length in front of the access port shall be 2m or the length of the probe (which includes nozzles, suction/support tubes and associated filter holders) plus 1m (whichever is the greater)
• The platform should be wide enough to prevent sampling equipment extending beyond the platform
• Where necessary hoists or lifts should be provided to transport sampling equipment
• The use of the sampling equipment should not be impeded by guard fences or other structures
Summary
By ensuring that monitoring arrangements are considered at the design stage of a new plant it should be possible to ensure that stack emission monitoring measurements are both reliable and compliant with legislation.
References
EN 15259:2007 - Air Quality - Measurement of stationary source emissions - Requirements for measurement sector and sites and for the measurement objective, plan and report.
Agency Technical Guidance Note M1 Sampling requirements for stack-emission monitoring.
Author
Dave Curtis
The Source Testing Association (STA) is a non-profit making technical trade association which was established in 1995 and has a corporate membership of over 200 companies from process operators, regulators, equipment suppliers and test laboratories.
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