What do the designations A, B, C, D, and E grades of cargo define?

The designation of grades A, B, C, D, and E for cargo specifically refers to classes that define the flash point range and Reid vapor pressure index of petroleum products. This classification system is crucial for understanding the safety and handling requirements of various petroleum products, particularly regarding their volatility and flammability. The flash point indicates the lowest temperature at which a liquid can vaporize to form an ignitable mixture in air, while the Reid vapor pressure is a measure of the volatility of a liquid.

Understanding these properties helps tankerman assistants and other personnel determine appropriate safety measures during loading, transporting, and unloading activities. This knowledge is essential for preventing accidents and ensuring compliance with regulations related to the handling of liquid cargoes, as different grades will dictate different safety protocols.

The other options, while related to petroleum products, do not directly reference the specific grading system defined by A, B, C, D, and E grades. The degrees of quality and properties concerning pour point, color, and viscosity index are important but do not accurately capture the meaning of the designations in this context.