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46 A P P E N D I X B This appendix provides a starting point proposal for discus- sion of a system that could be used to classify water-reactive substances for transport. Candidate Classification System Classification of Substances as Water Reactive This classification would apply to substances that in con- tact with water emit flammable or toxic gases during testing, as outlined in Appendix C of this report: 1. Spontaneous ignition of the emitted gas takes place in any step of the test procedure; 2. There is evolution of a flammable gas at a specific rate of gas evolution greater than 1 l/kg-hr; or 3. There is evolution of a toxic gas with an LC50 (based on testing with albino rats and 1 hour exposure) less than 5000 ml/m3 (ppm) at a specific rate of gas evolution greater than 1 l/kg-hr. Categorization into SubgroupsâSubstances Evolving Flammable Gases Substances should be categorized as subgroup I (most haz- ardous) should they be found to react vigorously with water at ambient temperatures and demonstrate generally a ten- dency for the gas produced to ignite spontaneously, or should testing measure a specific rate of flammable gas evolution at ambient temperatures equal to or greater than 10 l/kg-min. Substances should be categorized as subgroup II (mod- erately hazardous) should testing measure a specific rate of flammable gas evolution at ambient temperatures equal to or greater than 20 l/kg-hr and if the substance does not other- wise qualify for subgroup I. Substances should be categorized as subgroup III (least hazardous) should testing measure a specific rate of flamma- ble gas evolution at ambient temperatures equal to or greater than 1 l/kg-hr and if the substance does not meet the criteria for subgroups I or II. Categorization into SubgroupsâSubstances Evolving Toxic Gases Substances should be categorized as subgroup I (most hazardous) should testing measure a specific rate of toxic gas evolution at ambient temperatures equal to or greater than 1 l/kg-hr, when the gas produced would be classified as a Division 2.3 toxic gas according to sub-section 2.2.2.1(b) of the UN Model Regulations or is already listed as a Division 2.3 substance in the Dangerous Goods List of Chapter 2.3 of the UN Model Regulations, and when the ratio of the LC50 (based on testing with albino rats and 1-hour exposure) in units of ml/m3 (ppm) to the specific rate of toxic gas evolution in units of l/kg-hr is less than or equal to 1 (see Figure B-1). Substances should be categorized as subgroup II (moder- ately hazardous) should testing measure a specific rate of toxic gas evolution at ambient temperatures equal to or greater than 1 l/kg-hr, when the gas produced would be classified as a Divi- sion 2.3 toxic gas according to sub-section 2.2.2.1(b) of the UN Model Regulations or is already listed as a Division 2.3 sub- stance in the Dangerous Goods List of Chapter 2.3 of the UN Model Regulations, and when the ratio of the LC50 (based on testing with albino rats and 1-hour exposure) in units of ml/m3 (ppm) to the specific rate of toxic gas evolution in units of l/kg-hr is less than or equal to 20, and when the substance does not otherwise meet the criteria for subgroup I (see Figure B-1). Substances should be categorized as subgroup III (least hazardous) should testing measure a specific rate of toxic gas evolution at ambient temperatures equal to or greater than 1 l/kg-hr, when the gas produced would be classified as a Divi- sion 2.3 toxic gas according to sub-section 2.2.2.1(b) of the UN Model Regulations or is already listed as a Division 2.3 sub- stance in the Dangerous Goods List of Chapter 2.3 of the UN Model Regulations, and when the substance does not otherwise meet the criteria for subgroups I or II (see also Figure B1). Proposed Classification System
47 Figure B-1. Chart illustrating the categorization of substances that in contact with water emit toxic gases.
