DETERMINATION OF SELF-ACCELERATING DECOMPOSITION TEMPERATURES FOR SELF-REACTIVE SUBSTANCES

A self-accelerating decomposition temperature (TSADT) is the lowest ambient air temperature at which a self-reactive substance undergoes an exothermic reaction in a specified commercial package in a period of seven days or less. The same substance and package must be able to survive for seven days at a temperature within 6-degrees-C of the temperature at which the reaction occurred. A TSADT is determined for the purpose of deciding whether a self-reactive substance should be subject to temperature control during transport. We have re-examined the established T(SADT) test methods to clarify their application, affirm their validity and extend them to a wider range of materials. Two of the four test methods recommended by the United Nations Orange Book1 require calculations to determine a T(SADT). Our proposed method, which uses Accelerating Rate Calorimeter (ARC) data, requires similar calculations to determine a T(SADT). To ensure determination of conservative values when using any of the methods for self-reactive substances, the investigator should 1. consider pressure increases and potential package failure due to non-condensable gas formation and 2. account for the effects of a non-uniform temperature distribution within a viscous liquid, paste or solid by using the Frank-Kamenetskii thermal explosion model. Methodologies are discussed which address both of these areas. Also discussed is a method to account for the effect of reactant depletion on predicted T(SADT) values for both the Semenov and Frank-Kamenetskii thermal explosion models. This correction can be significant and is required to ensure that analytical values agree with experimental values.