Which of the following is NOT allowed for the storage of flammable and combustible liquids?

The correct choice indicates that the use of metal barrels for the storage of flammable and combustible liquids is not permissible. Generally, metal barrels can be used for the storage of flammable and combustible liquids, provided they meet certain safety standards and regulations. The main issue likely stems from the specific requirements or limitations present in particular codes or standards that govern the storage of hazardous materials.

For effective storage of flammable and combustible liquids, options like portable tanks, intermediate bulk containers, and fiber drums are frequently allowed as they are designed to safely contain such materials and often come with features that help in preventing leaks, spills, or explosions. These containers are typically built with materials and designs intended to minimize risks during the storage and handling of hazardous substances.

In contrast, metal barrels might not meet all regulatory standards in specific situations, leading to their prohibition in certain contexts. Understanding the conditions under which various containers can or cannot be used is crucial for compliance with safety regulations in the supervision of smoke detectors and other fire safety measures.