EXECUTIVE SUMMARY

1

1

INTRODUCTION

16

Charge to the Committee

17

Conceptual Framework of the Report

21

PART I
CURRENT APPROACHES TO RISK ASSESSMENT

23

2

RISK ASSESSMENT AND ITS SOCIAL AND REGULATORY CONTEXTS

25

General Concepts

25

Historical Roots

29

NRC Study of Risk Assessment in the Federal Government

33

Events After Release of the 1983 NRC Report

34

Uses of Risk Assessment in the Regulation of Hazardous Air Pollutants

36

Noncancer Risk Associated with Hazardous Air Pollutants

39

Public Criticism of Conduct and Uses of Risk Assessment

40

3

EXPOSURE ASSESSMENT

43

Introduction

43

Emission Characterization

47

Modeling Used in Exposure Assessment

50