In this first of two related articles, Robyn Fairman examines the use of risk assessment in environmental health regulation and enforcement

Absolute safety is an unachievable goal. Increasing scientific knowledge improves our understanding of the risks posed by environmental health hazards, but can undermine accepted "credos" about how to control them. Legal and policy frameworks designed to protect the public from environmental health hazards are changing. This is due to the recognition that in most instances "safe" is an unrealistic aim - either because of the inherent nature of the hazard, or the feasibility, economic and social cost implications of achieving safety. As politicians, regulators and enforcers accept that all activities carry some risk, regulation in environmental health is increasingly aimed at risk reduction.(4)

Risk assessment is used to enable decisions to be made about managing risks. It has become a major tool in environmental health regulation.(22,23) White papers on the Government, the Food Standards Agency, the environment and the UK's Environmental Health Action Plan all refer to the need for effective assessment of risks and risk management based upon sound science.(6,12,13,22,23,26) Environmental health practitioners will be expected to assess and manage risks within regulatory and policy frameworks.

This range of use and differing nature of assessments has led to immense difficulties in terminology.(24,32,38) Methodological debates have led to opposing methodologies with the engineering base of health and safety risk assessment not being easily translatable to other areas of environmental risk.(30,38) The Government has attempted to clarify meaning and methods through the Interdepartmental Liaison Group on Risk Assessment and the Interdepartmental Group on Health Risks from Chemicals.(22,23,33-36) A huge wealth of academic and policy literature exists on the nature of risk assessment, its use and misuse.(1,32,37)

Risk is a difficult concept. Risk assessment varies between hazard areas and the scientific definition of risk may differ from the legal definition. Until practitioners understand what risk means, and the basis of risk assessment schemes, they will find enforcing risk-based legislation difficult and their decisions will be open to challenge. There are many types of risk assessment. Quantitative risk assessments take time, money, skill and large amounts of data. The effort involved needs to be justified by the demands that will be put on the assessment.

Uses of risk assessment in legislation
Risk assessment in legislation has two main uses:
- The enforcer requires the risk creator to assess risk eg the Management of Health and Safety at Work Regulations 1999 (MHSWR) and the Control of Major Accident Hazards Industries Regulations 1999 (COMAH).
- The enforcer carries out a risk assessment in order to determine appropriate regulatory controls. Decisions as to what is "as low as is reasonably practicable"(ALARP) under health and safety legislation are an example. These decisions are normally non-formalised and based upon professional judgement. A recent innovation is the use of formalised risk assessment for enforcement decision-making. Decisions on contaminated land will be based upon a formalised evaluation of risk.(14)

prioritise risks for action
Risk assessment required by legislation must be proportionate to the risk. If major hazards causing large risks exist, a more quantitative evidence-based assessment will be required, eg under COMAH detailed quantitative assessments are required. In low risk health and safety premises, an assessment proportionate to the risk can be qualitative and based upon experience. Under the MHSWR, risk assessment is purely a means to prioritise risks for action. Semi-quantitative or qualitative assessments are capable of doing this. The ranking numbers mean nothing, other than to enable ranking and prioritisation of risk reduction measures within that company. They cannot be compared with external risk criteria.

enforcement decisions
If risk assessment is to be used to make enforcement decisions, it must be robust enough to stand scrutiny by those who are regulated. Part of the reasoning for the use of risk assessment is to allow transparency into the system. This is a laudible aspiration, but one which will create difficulties if the risk assessment methods on which decisions are made are not beyond reproach. In the contaminated land regime, for instance, the remediation levels required by the regulator can be challenged on the basis of a more accurate risk assessment carried out by those who are regulated.(14) A range of contaminated land risk assessment models exist which give different answers with the same input data. Risk assessment has its roots in science but it is not a science in itself. A former director of the US Environmental Protection Agency described risk assessment as "a shotgun wedding between science and policy".(39)

Risk assessment methods have been developed as a way of trying to get the available science to answer policy-maker's questions. The UK's recent past of poorly managed risk issues is evidence that in many cases science cannot answer the questions posed by policy-makers in a way which is immediately of use. The role of professional judgement and assumptions have long been recognised as clouding assessments.(29) Until the DETR issue more guidance on contaminated land risk assessment, it is impossible to comment on the likely results of the use of risk assessment in this context. However, from experience in the US, we can be confident that we are in for a rocky ride.(5)

types of assessment
Ranking and qualitative schemes are acceptable for the majority of uses by environmental health practitioners. However, they cannot be used in controversial decisions or where decisions are being made solely on the basis of the risk assessment. Such methods can only indicate an estimate of risk, and where precision and accuracy are required are unreliable.

Qualitative approaches, due to their lack of empirical base, can only be used as part of a decision-making process. The limited information they provide can be used if there is awareness of the uncertainties and complexities involved. Ranking schemes with arbitrary estimates of frequency and severity are useful in prioritisation but have only a limited place in decision-making. Scoring methods can be used depending on the robustness of the underlying assumptions, data availability and weightings in the scoring system.

Enforcement decisions
To enable enforcement decisions to be made based upon risk, judgements as to whether a risk is "acceptable" or "tolerable" to society need to be made. In these circumstances quantitative values of risk need to be estimated, and then compared with criteria for acceptability or tolerability. Quantitative approaches are also needed where there is likely to be controversy involved in the decision, or where risks are great or the cost of reducing them large.

Quantitative values of risk
To quantitatively estimate risk it is necessary to establish how much of the hazard causes what degree of the harm that we are concerned with. This is called dose-response relationship or hazard characterisation.(7,8,28,18,33) The second element involves determining what degree of exposure to the hazard exists in the population we are concerned with, normally called an exposure assessment.(7,8,28, 34,35) The combination of these two elements gives an estimate of the risk. This last part, risk characterisation, must state all the assumptions made along the way and the uncertainties involved.(7,28,33) The state of current scientific knowledge contributes to uncertainty, and at present there is not enough data to be certain on most risk assessments. Assumptions have to be made in the presence of uncertainty.

The European legislation on new and existing chemicals provides a stark example of the difficulties in using quantified risk assessments as a decision-making tool. In some other areas, such as microbiological risk assessment, the difficulties in risk assessment are so large that qualitative assessments may be all that is possible at the moment and hazard analysis is recommended (CAC, 1995).(2) The current proposals on housing risk assessment and contaminated land face the same immense data uncertainties and gaps.

When is the risk tolerable?
If risk is a criterion to be used in legislation, there has to be a clear indication of when risk is tolerable to society. These criteria are rarely explicit. The HSE has defined risk tolerability and tolerability limits.(20) These have been derived from the nuclear industry but are applied to other manufacturing industries. They are based upon the concept of "revealed preference", where risk levels accepted in one risk area are used as a measure for what is acceptable in other risk areas. This concept is heavily criticised because of the need to compare different types of risk (for a good review see Loftstedt and Frewer).(25) It is questionable whether there is any basis for comparing risks from nuclear power to the risks posed to inhabitants in their homes. The basic problem is that risks are perceived differently. Risk estimates mean little, if not considered in context.(11)

The Royal Commission on Environmental Pollution recently stated: "Even if it is possible to estimate accurately the statistical probability of a specified event, that probability may not in itself be an appropriate basis for reaching a judgement about the tolerability of human activities that give rise to that probability."(37) Risk assessment cannot establish a relationship on any objective basis between risks of different types or between risks imposed on different groups, because to do so raises value issues. A conclusion of the RCEP report is:
"Making comparisons between risks which the public does not perceive as comparable can undermine the credibility of regulators and governments."
The Housing Hazards Rating Scheme has caused discussion in the environmental health practitioner community. The rating is to be used as a prioritisation scheme, a role it is suitable for. Its use in determining enforcement action is more questionable.

Variable meanings
A major question is how the courts will interpret the term "risk" in environmental health actions. The interpretation in Regina v Board of Trustees of the Science Museum highlighted the lay interpretation of the courts. In this decision, risk was defined in a way that most environmental health practitioners would see as hazard. This has implications for the use of risk assessment in legislative decisions. If courts do not interpret the term risk in a way that practitioners use it (even in occupational health and safety where risk is a clearly understood concept), risk assessment will be potentially very difficult to use.

Conclusions
There are as many risk assessment schemes as there are uses. Quantitative assessments can be used for most purposes but are resource, skill and data intensive. For most environmental health practitioner purposes, qualitative or semi-quantitative approaches may suffice. However, if enforcement decision-making is going to be based upon numbers, these estimates have to be meaningful. In such cases or in controversial areas, or where risk reduction is expensive, quantification is necessary.

Moving to formalised decision-making based upon quantitative estimates of risk can have serious repercussions. Formalised decision-making processes define the criteria on which decisions are made and their relative importance. Such definitions limit the decision-making criterion to those that can be quantified, and such exclude issues relating to values, emotion and equity. With our current knowledge it is hard to be certain about the quantitative estimates.

As the RCEP report points out, the experience of the formalised mechanisms for risk assessment in the US has not reduced disquiet about risk reduction.(37) The UK has a different approach to risk management, with a long history of risk-based approaches but little experience of formalised mechanisms.(17) Formalised mechanisms may increase disagreements about risk reduction as such evidence-based approaches cannot operate without good quality evidence and societally-agreed criteria for acceptable risk. In many risk areas, especially where the approach is novel, neither of these factors are present.

References
1. Adam J, 1995, Risk, UCL Press, London
2. Advisory Committee on Dangerous Pathogens, 1996, Microbiological Risk Assessment, ACDP, London
3. Battersby S and Ormandy D, 1999, "Surveying the System for Hazard Rating", Environmental Health Journal, Vol 107, 11, 356-359
4. Blair T, 1999, A new approach to regulation, speech to the Social Market Foundation, 27 April 1999
5. Breyer S, 1993, Breaking the Vicious Circle: Towards Effective Risk Regulation, Harvard University Press, Massachusetts
6. Cabinet Office, 1999, Modernising Government White Paper, Cm 4310, The Stationary Office, London
7. Commission of the European Communities, 1993, Commission Directive 93/67/EEC, OJ L227/10, 8 September 1993, Commission of the European Communities, Brussels
8. CEC/ECB, 1996, Technical Guidance Documents in Support of the Commission
9. Directive 93/67/EEC on Risk Assessment for New Notified Substances and the Commission Regulation (EC) 1488/94 on Risk Assessment for Existing Substances, Commission of the European Communities/European Chemical Bureau, Ispra
10. Danish Board of Technology, 1996, The Non Assessed Chemicals in the European Union, Danish Board of Technology, Copenhagen
11. Department of Health, 1999, Communicating about Risks to Public Health: Pointers to Good Practice, Department of Health, London
12. Department of Environment, 1990, This Common Inheritance, DoE, London
13. DoE and DoH 1996, UK National Environmental Health Action Plan, DoE/DH, London
14. DETR, 1999a, Draft Circular on Contaminated Land, HMSO, London
15. DETR, 1999b, Sustainable Production and Use of Chemicals, The Stationary Office, London
16. Fairman R, Williams WP, Mead C, 1998, Environmental Risk Assessment Approaches, Experiences and Information Sources, European Environment Agency, Copenhagen
17. Fairman R, 1999, "A commentary on 'The Evolution of environmental health risk management; A US Perspective'", Journal of Risk Research, 2, 2, 101-113
18. FAO/WHO, 1995, Application of Risk Analysis to Food Standards Issues, report of the Joint FAO/WHO Expert Consultation, Food and Agriculture
19. HELA, 1997, Advice to Local Authorities on Inspection Programmes and an Inspection Rating System, LAC67/1 (rev), HELA, London
20. HSE, 1992, The Tolerability of Risks from Nuclear Power Stations 2nd Edition, HMSO, London
21. HSE, 1999, Reducing Risks Protecting People, HSE, Suffolk
22. Interdepartmental Liaison Group on Risk Assessment, 1996, Use of Risk Assessment Within Government Departments, HSE, London
23. Interdepartmental Liaison Group on Risk Assessment, 1999, Risk Assessment and Risk Management, Improving Policy and Practice within Government Departments, HSE, London
24. Kaplan S, 1997, "The Words of Risk Analysis", Risk Analysis: An International Journal, 17,4,407-419
25. Loftstedt R and Frewer L, 1998, Risk and Modern Society, Earthscan, London
26. MAFF, 1998, The Food Standards Agency, A Force for Change, MAFF, London
27. MAFF/DH, 1999, Code of Practice No 9 Food Hygiene Inspections, MAFF/DoH, London
28. NAS, 1983, Risk Assessment in the Federal Government: Managing the Process, National Academy of Sciences, National Academy Press, Washington DC
29. NAS, 1994, Science And Judgement In Risk Assessment, National Research Council, National Academy Press, Washington DC
30. NAS, 1996, Understanding Risk: Informing Decisions In A Democratic Society, National Research Council, National Academy Press, Washington DC
31. R v Board of the Trustees of the Science Museum, 1993, 1WLR 1171
32. Renn O, 1998, "Three decades of risk research", Journal of Risk Research, 1,1,49-73
33. Risk Assessment and Toxicology Steering Committee, 1999a, Risk assessment approaches used by the UK government for evaluation human health effects of chemicals, Institute of Environment and Health, Leicester
34. Risk Assessment and Toxicology Steering Committee, 1999b, Exposure Assessment in the Evaluation of Risks to Human Health, Institute of Environment and Health, Leicester
35. Risk Assessment and Toxicology Steering Committee, 1999c, Risk strategies in relation to population subgroups, Institute of Environment and Health, Leicester
36. Risk Assessment and Toxicology Steering Committee, 1999d, Physiologically-based pharmacokinetic modelling: A potential tool for use in risk assessment, Institute of Environment and Health, Leicester
37. Royal Commission for Environmental Pollution, 1998, 21st Report, Setting Environmental Standards, The Stationary Office, London
38. Royal Society, 1992, Risk: Analysis, Perception and Management, Royal Society,
39. Ruckleshaus WD, 1983, Science, 221, p1026

App. 1: Types of risk assessment schemes
* Risk assessment can be quantitative, and provide numerical estimates of risk. This can be expressed as the number of deaths from exposure over a period of time to a certain hazard. Examples of quantitative risk assessments are those used in setting occupational exposure limits.

* Semi-quantitative assessments are usually ranking schemes. They are based upon judgements of severity and frequency and rank the hazard in relation to other hazards being examined. They do not produce an estimate of risk, only a ranking. The majority of assessments carried out under the Management of Health and Safety at Work Regulations 1999 are semi-quantitative rankings.

* In Scoring systems, quantitative data on health effects and exposure is used by a skilled person to create a scoring scheme. The relationships between hazards, exposure and effect are analysed, and weighted to create a scoring system for hazards. These schemes can be used by less skilled practitioners to score the hazards. With careful construction of the attributes, a system is produced that can enable rough "estimates" of risk to be calculated. The prioritisation scheme for inspection frequencies in food hygiene and health and safety are examples of crude scoring systems.(11 19) The proposed Housing Hazards Rating scheme is an example of a more complex scoring method.

* Qualitative assessments are based upon the judgement and expertise of the assessor. They may be based upon the same matrix approach as semi-quantitative assessments but frequency and consequence will be judged as high, medium and low.

App. 2: European action on new and existing chemicals

Under a European Directive and Regulation new and existing chemicals have to be risk assessed and decisions are made on risk reduction on the basis of the risks posed to human health and ecosystems.(7)
In 1993, the EU began to assess the risks of the 100,000 existing and 2,000 new chemicals. About 1,500 chemicals account for in excess of 95 per cent of total chemical production. There are huge data deficiencies even for this group. For most chemicals, even base set data is incomplete. This can only allow an initial or preliminary assessment of risk.(10)
More than 10,000 existing chemicals will be on the database by the end of 1998. Available finances are only sufficient for an adequate assessment of about 20-30 chemicals per year. Assessments of 10 chemicals were completed under the EU existing chemicals risk assessment programme by the end of 1997 (EEA, 1998). The UK Government introduced a fast-track assessment process within the new chemicals policy because of the complexity and length of time for assessments to be completed.(15)

App. 3: The use of "acceptability" criteria in the Housing Hazards Rating Scheme

In the proposed Housing Hazards Rating Scheme, a risk of one in 10,000 is defined as "acceptable". The criteria derive from the 1992 HSE publication The Tolerability of Nuclear Power Stations where one in 10,000 is the maximum "tolerable" risk for members of the public from any single non-nuclear plant.(3,20) "Acceptable risk" is defined as one in 1,000,000.(20) There is a problem with the incomparability of risks. Is the perception of the risks posed by a manufacturing plant the same as that of the risks posed by one's own home or by a landlord's inactivity? The HSE has recognised that tolerability criteria only apply in specific circumstances.(21)
A second problem is the use of a risk criteria that the HSE define as the line between where a practice is intolerable and tolerable, and which the Housing Hazards Rating Scheme is using to mean "acceptable". These are very different things.