What type of valve must not allow discharge from containers on vehicles to impinge upon other components?

The correct choice emphasizes the importance of a pressure relief valve in ensuring safety during the dispensing and handling of LP-gas. A pressure relief valve serves a critical role by allowing excess pressure to be released from a container, thereby preventing potential hazards such as explosions or leaks that could occur if the pressure builds up too high.

In situations where containers are transported on vehicles, it is vital that the discharge from these valves does not negatively impact other components or create hazards. By design, pressure relief valves are engineered to release pressure in a controlled manner, thereby minimizing the risk of gas escaping in a way that could affect equipment, personnel, or the environment.

In contrast, other types of valves, such as shutoff valves and ball valves, primarily function to control or stop the flow of gas rather than manage excess pressure. Safety relief valves do offer additional protection but are not necessarily designed to prevent discharge from affecting surrounding components in the same way that pressure relief valves are specifically intended to do. Thus, the emphasis on preventing impingement on other parts during container discharge aligns perfectly with the functions of a pressure relief valve, validating it as the most suitable answer for the question posed.