Posted: 2001
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Article SummaryThis manual on how to use risk comparisons and risk statistics was commissioned to help chemical plant managers explain air emissions to their neighbors. Chapter III on risk comparisons, especially, is still relevant. Later research hasn’t borne out all its seat-of-the-pants conclusions, but the advice at the end of the chapter about the worst risk comparisons holds firm – in my terms these comparisons fail (especially when people are outraged) because they try to compare the hazard of high-outrage and low-outrage risks. The other chapters are also useful and not really outdated, I think. The appendices are both outdated and all too likely to be misused. They’re what the client originally wanted most. Vincent Covello, Paul Slovic, and I wrote the rest of the manual to soften them.

Risk Communication, Risk Statistics,
and Risk Comparisons:
A Manual for Plant Managers

Washington, DC: Chemical Manufacturers Association, 1988

Part V
Anticipating Objections to
Explanations of Chemical Risks

Conclusion and Acknowledgements

Part V
Anticipating Objections to
Explanations of Chemical Risks

Various objections can be anticipated in response to explanations of risk-related information, including risk comparisons. Some of these objections have already been discussed. However, other objections can be anticipated that are related to (1) data uncertainties, (2) information disclosure, and (3) demands for zero risk.

Data Uncertainties

Since risk data are often highly uncertain, some people are likely to object that the data are too uncertain to trust. In addressing this issue, several guidelines can be helpful. (For more details, see Hance, Chess and Sandman, 1987.)

number 1

Acknowledge – do not hide – uncertainty. Sounding more certain than the data can justify is a sure path to losing trust and credibility. Sources of uncertainty – for example, uncertainties due to generalizing from animal data to humans, gaps in the data, and differences of interpretation – should all be acknowledged up front, not “admitted” belatedly when an opposing interest group points them out. But acknowledging uncertainty is not the same thing as asserting total randomness or declaring ignorance.

Degree of certainty can be represented along a scale or continuum, from “total confidence” in the data to “guesswork” (in science there is never complete certainty, since new evidence can always overturn previous beliefs). When you have total confidence in the data, do not hesitate to say so. Most of the data produced by risk assessments, however, are somewhere in the middle of the scale. Such data are characterized by uncomfortably large margins of error; often they are based on disputable assumptions, models, and extrapolations, such as those from animals to people, from high doses to low doses. Nonetheless, such data are a much better basis for decision and action than guesswork. In these cases, assert frankly that the information is helpful but far from certain. Then explain that risk assessments deal with this uncomfortable level of uncertainty by making assumptions in the direction of overestimating the risk.

Somewhere near the “guesswork” end of the scale are risk assessments based on very inadequate data. When that is the case, say so. State as much as is known and explain (a) what you propose to do to get better risk data, and (b) what you propose to do in the meantime to reduce or protect people against the risk. Projecting this attitude is crucial. Under Title III, communities may begin asking about many possible health and environmental consequences for thousands of different chemicals. In many cases little or no data are available to answer these questions. When you have no evidence one way or the other, such as in the case of data on the relationship between air toxic X and miscarriages, never respond with “There is no evidence to show that air toxic X causes miscarriages.” The statement is technically correct – but profoundly misleading. If similar compounds have been tested and found not to cause miscarriages, say that. If there are theoretical reasons for doubting that air toxic X could interfere with pregnancies, say that. If you have carefully kept track of and monitored female plant employees and found no miscarriage problems, say that. And if the possible connection is still untested and deserves to be studied, say that.

number 2
In some cases, risk estimates are very uncertain because the risk is very low and measurement is very difficult, such as in cases of the chronic effects of chemicals with extremely low toxicity. In these cases you are best off explaining that the data are uncertain because it is so hard to measure such improbable effects.
number 3

In acknowledging and explaining data uncertainties, talk about how the risk estimate was obtained, and by whom. Demystifying the risk assessment process is a public benefit in its own right and will help your audience understand why you are simultaneously claiming (a) that your risk estimate is uncertain and (b) that your estimate is based on the best available scientific data. Explaining this process will also enable you to make points that are important for the audience to understand. Two points of special relevance and importance for the chemical industry are as follows.

First, the presence of a toxic chemical in the environment, such as an emission from a manufacturing plant, does not necessarily signify a significant health or environmental risk. This point is often extremely difficult to communicate, especially to those worried about long-term, low-dose effects. Even if hundreds or thousands of tons of air toxics are emitted into the air each year, there may be no significant health or environmental risk to people. For a toxic chemical to expose a risk, an exposure must occur. There must be a way for the air toxic to get from where it is (the manufacturing plant) to where people or the things they value are. Routes of exposure are as important in risk assessment as toxicity measurements are.

Second, when a route of exposure exists, the next important question is the concentration of the chemical that may reach people. This concentration amount, typically far lower than the concentration at the source, will often become even lower with the passage of time as the substance breaks down. Risk assessors consider not only whether a toxic substance is in the air or groundwater but also how much is in the air or groundwater.

This distinction becomes more important as measurement equipment becomes better. By means of their ability to measure parts per trillion and parts per quadrillion, scientists are now able to detect “low but measurable” chemical concentrations that were unknown before. Thus the proper question is not “How risky is a toxic substance?” but rather “How risky is the concentration of the toxic substance to which people are being exposed?”

number 4
Regardless of how you explain uncertainty in risk estimates, some people will still be dissatisfied. The demand for certainty is a natural human trait, especially in stressful situations when we feel helpless, angry, or at the mercy of other people. Often community members will suggest ways of improving the quality of risk assessment data. These suggestions are worth taking seriously, not only for their technical information, such as information on exposure routes that may have been overlooked, but as a means for reassuring the community that you are listening, that you care about their concerns, and that you are willing to be responsive. Although absolute certainty can never be achieved, community proposals for striving for that goal deserve respectful attention. But remember: Never promise you will do something if you cannot do it.

Information Disclosure

In some cases, risk data are quite preliminary. The company may want to delay releasing the information until further testing has been done. In addressing this issue, two general guidelines can be helpful to you. (For more detail see Hance, Chess and Sandman, 1987.)

number 1
Uncertainty is seldom if ever an acceptable excuse for waiting to communicate risk information. Especially if the information is alarming, it should be released promptly (with appropriate reservations about its reliability). This disclosure may be a legal obligation in some situations, and an ethical obligation in nearly all situations.
number 2
Almost without exception, it is better to announce a possible problem right away than to be accused later of having covered one up. Of course common sense is the rule. Often the preliminary data are highly unreliable and emergency action would not be warranted. In such cases, you may prefer to wait a week or two for retesting and quality control, rather than start a furor over nothing. But no plant manager with unsettling risk data is likely to be tempted to announce the data prematurely. Rather, your temptation – a very dangerous one – will be to wait too long. The worst of all possible worlds is to have an investigative reporter, an environmental activist, a disaffected employee, or a regulatory agency discover and announce the problem. Do not wait for that to happen (it will). And do not wait until the problem is solved or until all the scientific data are in. As soon as you reasonably can, announce what you know and what you propose to do about it.

Demands for Zero Risk

One of the predictable things that will happen when you explain a risk number is that someone in the audience will point out that it is not zero, following up with the assertion that it should be. Explain that zero risk does not exist. Explain that we all habitually – if ignorantly – tolerate quite substantial and avoidable risks, including smoking and driving without seatbelts fastened. Explain that it is an impossible demand to expect zero risk from a chemical company.

How you specifically respond to the demand for zero risk will depend on your assessment of its source. Consider five possibilities:

number 1
The demand for zero risk may be reasonable. The plant may be able to (in effect) eliminate virtually all the risk in question through some change in procedure. If so, consider the costs and benefits of doing so. If the situation warrants, you should agree to take action.
number 2
The demand for zero risk may be an exaggerated way of making the point that the risk is too high. In these cases, the demand is in effect a negotiating position. Your response to this demand may be complicated by the fact that although further risk reduction is entirely feasible, the remaining risk is insignificant and such action simply makes no economic sense. However, for several reasons, you should not point out the economic benefits that compensate for risks that will not be eliminated. First, given the high value people attach to good health, the public will generally reject the argument that the reduced risk to the community does not justify the added costs to the company. Second, if you contend that the benefits compensate for the risks, you expose the company to accusations of bribery and blackmail. Finally, since economic benefits are typically distributed differently from health and environmental risks, such arguments often raise serious problems of fairness and equity.
number 3
The demand for zero risk may be sincere but ill-informed. The people making it may simply not understand why something that is known to be risky can be allowed to continue. If so, respond gently with some fundamental risk education. Explain (as above) that zero risk is non-existent. Point out that all of life’s activities carry some risk, which we usually ignore if the risk is small enough and if the activity is beneficial enough. Be sure to agree that the risk should be made as low as possible, and discuss what you are doing to achieve the lowest possible level.
number 4

The demand for zero risk may be politically motivated. The demand may be designed to win followers, influence politicians, or attract the interest of journalists. Such political activity is perfectly legitimate in a democracy. Groups opposed to the chemical industry – whether they are staffed by volunteers or paid organizers – are often highly dedicated and committed to their cause. Just as the chemical industry – as an industry – is entitled to build its political case, opponents of the chemical industry are also entitled to build their political case. With occasional exceptions, the strategies used by opponents are legitimate political strategies. For example, an opposing group may appeal to the community’s health concerns, just as the chemical industry may appeal to the community’s economic concerns. An opposing group may recruit and mobilize experts to support its view, just as the chemical industry may recruit and mobilize experts to support its view. Given that such activities are entirely legitimate in a democracy, you will find it unwise to attack the sincerity or legitimacy of opposing groups. A plant manager – or the chemical industry as a whole – has a legitimate right to disagree with the view of an opposing group. Disagreeing, however, is not the same as questioning the integrity of an opposing group or the right of the opposing group to use legitimate political strategies to promote its views.

If the demand for zero risk is politically motivated, you are unlikely to make much headway in meetings held in public settings. One of your main options is to try to arrange a private or semi-private meeting, where frank discussion and negotiation might be possible. In public settings, your best strategy is to clarify your position as best you can, following the advice offered in this manual.

number 5
Finally, the demand for zero risk may be a reflection of emotional distress stemming from outrage, anger, and distrust. Some people in the community may have decided that you are the enemy; that the company is uncaring, arrogant, and dishonest; or that chemical manufacturing is an industry that does society little benefit at great cost. Risk, then, may not be the central issue. If a small number of community residents adopt a hostile view, you can probably do little to change their minds. But if the outrage, anger, and distrust are widespread, consider those reactions as symptoms of serious problems in your overall communication effort or in your overall health and environmental protection effort. You must address yourself to the underlying antagonism and begin the slow, hard work of building bridges. In short, talking about risk to an audience that wants to believe that the risk is high is a pointless undertaking. Figure out why the audience feels as it does, and pay more attention to those issues than to the battle over zero risk.


As stated in the beginning of this manual, there are no easy prescriptions for effective risk communication. There are also limits on what one chemical plant manager – no matter how skilled, committed, and sincere – can do. However, the rules, guidelines, advice, and specific examples offered in this manual can help. Over the next few years, effective risk communication will become increasingly important for the chemical industry. The industry as a whole, and plant managers in particular, will continually be challenged and asked to provide information about chemical risks to employees, customers, and the general public. As a plant manager, your response to this challenge will have an effect on public response to the chemical industry for years to come.


This manual is based in part on material developed during an intensive two-day workshop co-chaired by the authors and sponsored by the Chemical Manufacturers Association. The following persons attended the workshop and collaborated in the writing of the manual. We would like to thank them for their substantive contributions and for their comments on earlier drafts:

  • David Baird, Exxon Chemical Americas
  • Richard N. Knowles, E. I. du Pont de Nemours & Co.
  • Brent McGinnis, Ashland Chemical Co.
  • Timothy O Leary, Chemical Manufacturers Association
  • John E. Slavick, Chemical Manufacturers Association
  • Richard Symuleski, Amoco Chemical Co.
  • Ben Woodhouse, Dow Chemical U.S.A.

We would also like to express special thanks to John Slavick, Robin Higgins, and the Chemical Manufacturers Association for organizing the workshop, for their assistance, and for supporting the production and publication of this manual.

Parts of the manual are also based on several papers and reports that we co-authored.

Hance, B., C. Chess and P. Sandman (1987), Improving Dialogue with Communities: A Risk Communication Manual for Government. Trenton, New Jersey, Office of Science and Research, New Jersey Department of Environmental Protection, December 1987.

Covello, V. and F. Allen (1988), Seven Cardinal Rules of Risk Communication, Washington, D.C.: U.S. Environmental Protection Agency, Office of Policy Analysis.

Covello, V., D. von Winterfeldt and P. Slovic (1987), “Communicating Risk Information to the Public,” in Risk Communication, edited by J.C. Davies, V. Covello and F. Allen, Washington, D.C.: The Conservation Foundation.

We would like to thank the co-authors of these papers and reports for allowing us to use material from these works.

Copyright © 1988 by Chemical Manufacturers Association

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