Determination of SADTs Using Accelerating Rate Calorimeter

Safe storage, proper handling, and dependable transport of self-reactive substances are fundamental operations required in the chemical process industries. One of the key parameters used to assess the extent of a substance’s reactivity is its self-accelerating decomposition temperature (SADT). Various methods for estimating the SADTs have been well documented, including the “Recommendations on the Transport of Dangerous Goods: Manual of Tests and Criteria” by the United Nations. In this paper, using the Accelerating Rate Calorimeter (ARC) to assess SADT is the primary focus. Styrene polymerization and its applicable inhibitor effectiveness, including loss of inhibitor, are evaluated. Presented as a case study, a detailed kinetic model is developed illustrating the ability and flexibility to calculate the SADTs for any package sizes, shape and configurations. Complete simulations of time to reactions thermal runaway for selected DOT storage and transport vehicle are also included.

 A reactive chemical which decomposes exothermally when held in a container will either come to a thermal equilibrium or self-heat, depending on the heat generation rate and heat loss rate of the system. Given that heat generation rate is exponential to temperature and heat loss rate is linear to the temperature, an increase in temperature will result in a heat accumulation, potentially leading to thermal runaway and possible explosion. According to The United Nations Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, a self-accelerating decomposition temperature (SADT) is the lowest ambient air temperature at which a self-reactive substance undergoes an exothermic reaction in a specified package in a period of seven days or less. The same sample and package must be able to survive for seven days at a temperature within 6°C of the temperature at which the reaction occurs. SADT of self-reactive substance is determined to decide the safe storage and transportation temperatures in a specified package. Values are determined on the assumption that the substance will only be subjected to a maximum of 55°C for a brief period any day of storage or transportation. All substances having SADT temperature of 55°C or less, should be subjected to a controlled environment for storage and transport. There are four test methods recommended by the United Nations (UN) for SADT determination, which mainly differ in measuring techniques.

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