Review of international criteria and mixture rules for health hazard classification.

The presentation of consistent hazard information in the face of conflicting inter- and intranational regulations and standards is a formidable task. The principal challenge arises from the varying definitions of what is and is not a hazardous chemical and the differing rules that regulate the disclosure of components on material safety data sheets (MSDS) and labels. Some of the effects on hazard communication of nine health hazard classification systems of the United States, Canada, and the European Union are analyzed. The additional complication of differing rules that govern the hazard classification of mixtures is also discussed. The combination of inconsistent hazard classification of individual chemicals and dissimilar mixture rules can result in different conclusions about the hazard classification of commercial products. Faced with this situation, hazard communicators must focus on developing clear statements of the health effects that may arise from overexposure to a chemical, which is the essential purpose of developing MSDS and labels. These statements may be distinct from the terminology derived from the various classification systems. All national MSDS systems make provisions for including statements of hazard and also for providing the toxicology information that is the basis for translation into the locally governing classification terminology. Requirements for labels are often more restrictive, and the complete resolution of conflicting communication must await international harmonization of hazard classification systems including mixture rules.