Which of the following is not typically a function of a supply line?

The function of a supply line primarily revolves around the transportation of water from a source, such as a fire hydrant, to the area where it is needed, typically for firefighting efforts. This includes delivering water to the fire, feeding the attack line, and establishing connections to hydrants to ensure that sufficient water pressure and flow are maintained.

Providing ventilation, however, does not fall within the scope of a supply line's functions. Ventilation refers to the process of removing smoke, heat, and gases from a structure to improve visibility and decrease the potential for flashover, enabling firefighters to operate more safely and effectively. This task is typically managed through the use of tools and techniques to open windows, doors, or roofs rather than by the function of a supply line. Thus, identifying the lack of connection between ventilation and the purposes of a supply line clarifies why this option is not a function of such a line.