Test Procedures and Classification Criteria for Release of Toxic Gases from Water-Reactive Materials (2014)

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3 C H A P T E R 1 United Nations (UN) Model Regulations (2) currently encompasses substances that in contact with water emit flam- mable gas. As early as 1994, during the course of developing the Globally Harmonized System of Classification and Label- ing of Chemicals (GHS), it was noted that there were other regulatory systems that covered substances that in contact with water emit toxic gas (this, and much of the historical information in the next few paragraphs, is drawn from the Organisation for Economic Co-operation and Development’s [OECD’s] “Detailed Review Document on Classification in OECD Member Countries of Substances and Mixtures which in Contact with Water Release Toxic Gases”) (3). During development of the GHS, the OECD played a lead- ership role in the development of criteria for health hazards and was asked to lead in the development of criteria for sub- stances that on contact with water emit toxic gas. In doing so, the OECD reviewed existing national regulatory frameworks, including the following: • The Canadian Workplace Hazardous Materials Informa- tion System (WHMIS); • Annex III of European Union Directive 67/548/EEC: Nature of special risks attributed to dangerous substances and preparations; and • The U.S. DOT Hazardous Materials Regulations (HMR). The earliest OECD proposal (4) regarding classification and labeling of substances that on contact with water emit toxic gas included both gas evolution rate and gas toxicity criteria in the discussion, relying upon Test N.5 from Sec- tion 33.4 of the Manual of Tests and Criteria (1) for gas evolu- tion rate measurements. However, the classification criteria proposed in that document omitted consideration of the rate of gas production. When these criteria were presented to UN experts, there was concern that the OECD proposals did not address the rate of evolution of toxic gases (5). It was also recognized that international model regulations for the transport of dangerous goods did not address materials that emit toxic gases when exposed to water. This led to discussion of the only existing test for the rate of evolution of gases from water- reactive substances, Test N.5 from Section 33.4 of the UN’s Manual of Tests and Criteria, used to classify substances that are regulated in transport on the basis of their reaction with water and their evolution of flammable gases. Eventually discussion focused on the test itself, regarding (1) how to adapt it to substances that in contact with water emit nonflammable toxic gas (as opposed to substances that in contact with water emit flammable gas) and (2) how to improve the reproducibility of the test. To help address these issues, HMCRP undertook additional work on this topic. Background