Guidelines for Environmental Risk Assessment and Management
[This document refers, in a number of instances, to the then Department of the Environment, Transport and the Regions (DETR). The text of this document has not been updated since the transfer of environmental protection functions to Defra.]
Chapter 7
Evaluating the significance of a risk
7.1 Introduction
Along with the formal scientific assessment of the probability and magnitude of adverse impacts on the environment, the broader significance of an identified risk needs to be established as a basis for decision-making. To ensure that the outputs from a risk assessment help in decision-making a number of questions should already have been addressed (see US EPA, 1998; and Chapters 4, 5 and 6 of these guidelines).
- What impacts to the environment may occur?
- How harmful are these impacts to the environment?
- How likely is it that these impacts will occur?
- How frequently and where will these impacts occur?
- How much confidence can be placed in the results of the risk assessment?
- What are the critical data gaps and can these gaps be filled?
- Are further iterations to the risk assessment needed?
Evaluating the significance of a risk also involves determining the broader implications of the risk problem including social, political and economic considerations. Once these judgements are made about a risk's acceptability, decisions can be taken about how to reduce or manage the risk (Chapter 8).
7.2 Risk estimation as a basis for risk management decisions
For most activities it is likely that more than one hazard will be identified. For each separate hazard, combining the probability of the consequences and the magnitude of those consequences yields an estimation of risk. Both components are likely to be at best semi-quantitative and so each component will to some extent represent judgements on the basis of the knowledge and experience available. Issues relating to the probability of environmental consequences and how to deal with uncertainty are discussed in Chapter 6.
A simple matrix (Figure 7.1) can provide a consistent basis for decision-making. It should of course be used with caution, recognising the over-simplification that it will normally represent. The probability and consequences are defined according to parameters relevant to the situation; the boundaries of risk acceptability (and tolerability, where relevant) indicated on the matrix can be tailored to the factors influencing the significance of the risk (Section 7.3). Individual situations are mapped onto the matrix to provide a ready and consistent indication of their acceptability or tolerability.
| Figure 7.1 Estimation of risk from consideration of magnitude, consequences and probabilities | ||||
|---|---|---|---|---|
| Increasing acceptability
|
Consequences | |||
| Severe | Moderate | Mild | Negligible | |
| Probability | ||||
| High | high | high | medium/low | near zero |
| Medium | high | medium | low | near zero |
| Low | high/medium | medium/low | low | near zero |
| Negligible | high/medium/low | medium/low | low | near zero |
7.3 Factors influencing the significance of a risk
Statutory and policy requirements
A wide range of standards for pollution control exist in the UK including exposure standards, environmental quality standards, emission standards, process or operating standards and product standards. Clearly if these are legally mandatory and a risk assessment demonstrates that an intended activity is likely to breach them, the risk is unacceptable and measures to reduce it to acceptable levels should be adopted.
There is a substantial amount of legislation and numerous policy objectives that may affect the significance of a risk. Information sources are available which provide overviews and guidance on statutory requirements (Section 7.5).
In situations not covered by legislation, or where policy is to seek environmental improvements beyond those aspired to by statute, targets should be set through socio-economic analysis and expert judgement, taking account of the societal pressures which lead to policy or political decisions.
Value judgements
Defining what constitutes unacceptable harm to an ecosystem is a difficult task and ultimately depends on what values society places on ecosystems. Some hold the opinion that maintenance of ecosystem function is the main objective and that the loss of individual species may not be of consequence with respect to this. Maintaining ecosystem integrity, at local and global scales, is clearly important to the maintenance of an environment which provides the resources and conditions required for man's survival and development. The preservation of biodiversity in its own right has received much attention in recent years and many arguments have been put forward in support of this. Some habitats and species are considered to be of particularly high value for conservation, as a result of value judgements made on the basis of rarity, attractiveness, fragility and so on. The UK Government has set out priorities and strategies for biodiversity conservation in the UK Biodiversity Action Plan. These are reinforced by national statute implementing the EC Wild Birds Directive and the EC Habitats Directive.
Social aspects of risk
The acceptability of a risk can be significantly influenced by a range of psycho-social and political factors. These may include individual risk perceptions and attitudes, cultural values, questions of trust and credibility about risk proponents and managers, and questions of equity in risk distribution (Chapter 3). While risk management decisions should be based on the best scientific information available, these factors should also be considered when evaluating the significance of a risk. An important step is the creation of a constructive dialogue between stakeholders affected by or interested in risk problems (Section 3.8).
Economic considerations
Economic factors can have a significant influence on the decision-making process and may affect the acceptability of a given option. An example could be a town's flood defence. There are construction and maintenance costs associated with any flood protection scheme; there may also be costs in terms of damage to the environment by habitat removal or alteration. Various options to control the flood risk might be open to the Environment Agency. While it might technically be feasible to construct a flood defence scheme that protects against a one in fifty year flood event, the construction and maintenance costs of such a scheme are likely to be high. The Agency could, therefore, consider a scheme to protect against a more frequent but less harmful event, say a one in ten year flood. While the construction and maintenance costs of such a scheme would be lower, the costs in terms of damage to property from more severe but less frequent flood events might outweigh the financial savings in construction and maintenance costs.
The best option is likely to be the one with the greatest excess of benefits over costs, where the benefits are those accruing from protection (eg the damage or loss of property, materials, crops, human health and environmental assets that is avoided) and the costs are those social and private costs of the control options, including construction, maintenance and environmental damage. This should include both those benefits and costs that can be monetised and those that cannot (or for which robust monetary valuations are not readily available) - the latter need to be assessed in physical and qualitative terms. Because monetary values can more readily be assigned to some impacts than others, care is needed to ensure that adequate consideration is given in any decision-making to all non-monetised items that may be thought significant, relative to the monetised elements.
The changing environment and changing baselines
Baselines against which alternative risk assessment scenarios can be compared are likely to change over time. Changing baselines may be the result of a diverse set of factors including, for example, climate change, increasing urbanisation, demographic changes, changes in social attitudes towards risk acceptability and advances in technologies available to reduce risk. This can result in a new set of conditions against which existing risks and management options should be compared and altered if necessary. Clearly the possibility of such changes can have an impact on risk significance and should always be borne in mind.
7.4 Other significant factors
According to circumstances, UK statute or policy may subject an activity to requirements or principles to limit risk, as listed below:
| ALARA | as low as reasonably achievable |
| ALARP | as low as reasonably practicable |
| BATNEEC | best available technique not entailing excessive cost |
| BPEO | best practicable environmental option |
| BPM | best practicable means |
None of these terms is exactly equivalent to another. Generally they are used within a strict legal context, and consequently the use of one criterion rather than another needs to be considered carefully in each situation.
'As low as reasonably practicable' is a wide statement of principles and forms the cornerstone of nuclear plant safety. A risk that has been reduced to ALARP corresponds to the concept of tolerable risk. This implies that any further reduction in the risk can be achieved only at grossly disproportionate cost and that the benefits afforded by the risk are judged to outweigh the costs.
Other criteria commonly used in environmental risk assessment are described as BPEO and BATNEEC. Both these criteria involve balancing the reduction in risk with the practicability and cost of reducing that risk.
The application of BATNEEC normally means that the additional costs of avoiding environmental damage are justified by the benefits. Therefore, BATNEEC would not require the reduction of risk from 'low' to 'negligible' if that would require very expensive techniques. Under the Environmental Protection Act 1990, the BATNEEC criterion is applied in integrated pollution control (IPC) and in the management of risks from the release of genetically modified organisms to the environment.
Importantly, the application of BATNEEC means that the estimation of the risk associated with a particular activity can change over time as new techniques and technologies are developed, and the costs of existing techniques vary. Such changes may warrant another iteration of the whole risk assessment process. The BATNEEC criterion relies not only on technological solutions, but includes other approaches such as environmental management systems and staff training.
The BPEO is a term of policy guidance. It is the option which provides the most benefit or least damage to the environment as a whole, at an acceptable cost in both the long and short term. The BPEO, as a concept with legal basis, was introduced with IPC under Part I of the Environmental Protection Act 1990. Operators of prescribed industrial processes which produce releases to more than one environmental medium must ensure that BATNEEC is used to minimise pollution to the environment as a whole, having regard to BPEO. Again, an element of cost versus environmental benefit/risk is brought into play in deciding which process option constitutes BPEO. A key feature of the BPEO approach is that decision-making is transparent and that an audit trail exists so that all stages in the choice of the BPEO can be scrutinised.
Key references
For key references relating to the social aspects of risk see Chapter 3.
Biodiversity: The UK Steering Group (1995) Biodiversity: The UK
Steering Group Report, Volume 1: Meeting the Rio Challenge, London,
UK, HMSO
An account of the UK strategy for protecting biodiversity following
the Biodiversity Convention at the Earth Summit in Rio de Janeiro in June
1992. This volume sets out the basic action plan and includes the targets
for key species and habitats and the process of information gathering
with respect to UK biodiversity.
Biodiversity: The UK Steering Group (1995) Biodiversity: The UK
Steering Group Report, Volume 2: Action Plans, London, UK, HMSO
Following on from Volume 1, this gives more detailed information
on the species and habitats considered as priorities for conservation.
Action plans for the protection of a number of species/habitats are also
presented.
Calow P (1992) Can ecosystems be healthy? Critical consideration of
concepts. J Aquatic Ecosystem Health, 1, 1-5
An interesting discussion paper addressing the difficulties in
identifying the properties of undisturbed ecosystems and the whole concept
of the existence of 'healthy ecosystems'.
Calow P (1998) Handbook of Environmental Risk Assessment and Management,
Oxford, UK, Blackwell Science
A comprehensive treatment of the basic principles of environmental
risk assessment and management. Chapters discuss the way in which risk
assessment is used in decision-making for risk management for different
applications, highlighting important factors which may influence the significance
of a risk.
Douben PET, ed (1998) Pollution Risk Assessment and Management,
Chichester, UK, Wiley & Sons Ltd.
Provides an extensive discussion of the basic principles of integrated
pollution control and risk management.
Haigh N, ed (1992) Manual of Environmental Policy: The EC and Britain,
London, UK, Cartermill Publishing
This manual provides a complete account of EC environmental policy
and a comprehensive treatment of British policy that is relevant to the
implementation of EC legislation. First published in 1992, the manual
is regularly updated and two comprehensive releases are issued in May
and November.
HM Treasury (1997) Appraisal and Evaluation in Central Government:
Treasury Guidance, London, UK, TSO
This document deals with risk and environmental impacts as aspects
of the general appraisal framework for projects, programmes and policies.
Pearce DW & Turner RK (1990) Economics of Natural Resources
and the Environment, London, UK, Harvester Wheatsheaf
A book that provides background discussion of the economic principles
and practice relating to environmental resources and impacts.
Perrings C, Mäler K-G, Folke C, Holling CS & Jansson B-O,
eds (1997) Biodiversity Loss: Economic and Ecological Issues, Cambridge,
UK, Cambridge University Press
Contains useful discussions on the concepts of diversity, the implications
of biodiversity loss for ecosystem functioning, the driving forces behind
biodiversity loss, and the options for promoting biodiversity and conservation.
Royal Commission on Environmental Pollution (1998) Setting Environmental
Standards, Twenty-first Report, London, UK, TSO
A comprehensive review of the process of establishing standards
for environmental protection with recommendations for a more participatory
approach to their development.
US EPA (1998) Guidelines for Ecological Risk Assessment (EPA/630/R-95/002F),
Washington DC, USA, US Environmental Protection Agency
These guidelines were written to improve the quality and consistency
of ecological risk assessments. They should be of particular interest
to risk assessors and risk managers, highlighting and discussing important
principles and terminologies for the ecological risk assessment process.
Electronic information sources
CEDREC - A comprehensive computer database of UK and EC environmental legislation with easy-to-use cross-referencing and expert interpretation. Updated quarterly.
DETR internet site - www.dtlr.gov.uk
Environment Agency internet site - www.environment-agency.gov.uk
Environment Plus CD-ROM - Provides a wide range of information on the environment, including the full text of relevant EC and UK legislation plus the DETR's bibliographic database. Updated quarterly.
World Conservation Monitoring Centre internet site - www.wcmc.org.uk
Key periodicals
Atmospheric Environment
Conservation Biology
Environment
Environmental Science and Technology
Journal of Environmental Management
Journal of Risk Research
Marine Pollution Environment
Risk Analysis
Risk, Decision and Policy
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Page published 2 August
2000;
Page last modified
19 September, 2002