What safety feature must be equipped on containers according to NFPA regulations?

The correct answer, the overfilling prevention device, is crucial because it helps prevent accidents and spills that could lead to environmental contamination or safety hazards. According to NFPA regulations, containers that store flammable or hazardous materials must be equipped with features that enhance safety. An overfilling prevention device ensures that a container does not exceed its maximum capacity, significantly reducing the risk of incidents associated with spills or leaks.

While other options like an automatic shutoff valve and pressure relief valve are important in specific contexts and can contribute to safety, they do not specifically address the aspect of preventing overfilling in containers. A fire retardant coating may provide a level of protection against fire but does not directly relate to the safe handling and storage of liquids in containers in the same way that an overfilling prevention device does. Therefore, the focus on preventing overfilling is key to compliance and safety as mandated by NFPA regulations.