Explain the hazards and required handling precautions for self-reactive substances (Class 4.1).

Self-reactive substances, belonging to Class 4.1 of the IMDG Code, pose significant hazards due to their ability to undergo exothermic decomposition, meaning they can generate heat, pressure, and flammable gases without the presence of air. This decomposition can be triggered by heat, friction, impact, or contamination, potentially leading to a fire or explosion. Some self-reactive substances are also desensitized explosives, meaning they have explosive properties but are transported under Class 4.1 because they meet specific criteria for desensitization. The primary hazards associated with self-reactive substances are thermal instability, self-accelerating decomposition temperature (SADT), and the potential for explosion. The SADT is the lowest temperature at which self-accelerating decomposition may occur in the packaging as used in transport. If the ambient temperature exceeds the SADT, the substance can begin to decompose uncontrollably, leading to a thermal runaway. Required handling precautions include controlling the temperature, avoiding friction and impact, preventing contamination, and ensuring proper ventilation. Temperature control is crucial to maintain the substance below its SADT, often requiring refrigerated transport or specialized packaging with temperature indicators. Friction and impact can initiate decomposition, so careful handling procedures must be followed to avoid rough handling or dropping packages. Contamination with incompatible materials, such as acids, bases, or oxidizing agents, can also trigger decomposition. Proper ventilation is essential to prevent the buildup of flammable gases released during decomposition. Furthermore, self-reactive substances must be stowed away from incompatible materials and sources of heat. Emergency response procedures must be in place to address potential fires or explosions, including the use of appropriate firefighting agents and evacuation procedures. Therefore, strict adherence to handling precautions is essential to safely transport self-reactive substances.