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 The other chapters are also useful and not really outdated, I think. The appendices are both outdated and all too likely to be misused.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

Table of Contents and Introduction

Table of Contents

  • Guidelines and Rules for Effective Risk Communication
  • Actions versus Words
  • The Role of Risk Comparisons
  • Public Perceptions of the Chemical Industry
  • Factors Affecting Risk Acceptability
  • Disclosing and Providing Risk-Related Information
  • Spokespersons
  • Communication Channels and Media
  • Audiences
  • Types of Risk-Related Numbers and Statistics
  • Using Comparisons for Explaining Risk-Related Numbers and Statistics
  • Alternative Ways to Express Risk-Related Numbers and Statistics
  • Guidelines for Providing and Explaining Risk-Related Numbers and Statistics
  • Personalizing Risk-Related Numbers and Statistics
  • Purposes for Providing Risk Comparisons
  • Problems
  • Guidelines
  • A Categorization and Ranking System for Risk Comparison
  • First-rank Risk Comparisons
  • Second-rank Risk Comparisons
  • Third-rank Risk Comparisons
  • Fourth Rank Risk Comparisons
  • Fifth-rank Comparisons
  • First-Rank Risk Comparisons
  • Second-Rank Risk Comparisons
  • Third-Rank Risk Comparisons
  • Fourth-Rank Risk Comparisons
  • Fifth-Rank Comparisons
  • Data Uncertainties
  • Information Disclosure
  • Demands for Zero Risk



  • Table A.1:  Concentration Comparisons Organized by Unit Categories
  • Table A.2:  Miscellaneous Concentration Comparisons

  • Figure A.1:  Air Emissions from Chemical Production: Tons per Year Projected through 1988 for the Dow Chemical Company, Midland Division
  • Table B.1:  Annual Risk of Death in the United States
  • Table B.2:  Annual Risk of Death in the United States
  • Table B.3:  Risk Comparisons (Involuntary Risks Only)
  • Table B.4:  Estimated Loss of Life Expectancy Due to Various Causes
  • Table B.5:  Risks Estimated to Increase the Probability of Death in Any Year by One Chance in a Million
  • Table B.6:  Average Risk of Death to an Individual from Various Natural and Human-caused Accidents
  • Table B.7:  Average Risk of Death from Various Human-caused and Natural Accidents
  • Table B.8:  Ranking of Possible Cancer Risks from Common Substances

  • Figure B.1:  Health Risk Ladder
  • Figure B.2:  Upper Bound Estimates of Deaths for Different Energy Systems
  • Figure B.3:  Comparisons of Different Sources of Radiation Exposure
  • Figure B.4:  The Causes of Cancer: Quantitative Estimates of the Avoidable Risk of Cancer in the U.S.
  • Figure B.5:  Radon Risk Charts
  • Table C.1:  Factors Important in Risk Perception And Evaluation


The Emergency Planning and Community Right-to-Know Act (Title III of Superfund) and many state and local laws are imposing much more openness on the chemical industry. During the next few years, plant managers will increasingly be called upon to provide and explain information about chemical risks to employees, customers, and communities near chemical plants.

Plant managers can use this manual for practical guidance on providing and explaining information about chemical risks. A basic assumption of the manual is that risk communication, when done properly, is always better than stonewalling. In the long run, more effective risk communication will be better for plant managers, communities, and the chemical industry as a whole.

The manual consists of five substantive parts: (I) effectively communicating risk information; (II) guidelines for providing and explaining risk-related numbers and statistics; (III) guidelines for providing and explaining risk comparisons; (IV) concrete examples of risk comparisons; and (V) anticipating objections to explanations of chemical risks. The manual also includes a set of appendices containing tables of risk statistics and warning notes about the usefulness and reliability of the statistics.

Although this manual will not try to cover all aspects of risk communication, neither will it be confined to such narrow topics as risk comparisons. To be useful, the manual must also address closely related topics, such as how best to explain information on emission levels and concentrations of chemicals in air and water. A short bibliography is provided at the end of the manual for those interested in pursuing these topics in greater depth.

Most of the material in the manual focuses on providing and explaining data on health risks, especially long-term data. The emphasis is not on providing and explaining information about the risks of accidents. In some cases, accidents raise similar communication issues — especially when most of the expected adverse health effects are long-term rather than acute. However, in dealing with risks of accidents, it is generally both more relevant and more reliable to focus on preventive measures, emergency response procedures, containment and remediation procedures, and the extent of the possible damage.

Copyright © 1988 by Chemical Manufacturers Association

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