What is the numerical length designation for straight portable ladders?

The correct choice regarding the numerical length designation for straight portable ladders is that it is marked on each end of each rail within 12 inches of the end. This marking convention is critical for ensuring that firefighters and other personnel can easily identify the length of the ladder quickly and efficiently during operations.

Having the markings on both ends of the ladder provides flexibility and convenience, as it allows the user to determine the length regardless of how the ladder is positioned or how it is being retrieved. This is especially important during emergency situations where time is of the essence.

The other choices describe different locations for markings that do not align with standard practices for ladder length designation. For example, marking at the middle of each rail or only on the ladder's feet would make it more challenging for personnel to quickly assess the ladder's length, particularly when the ladder is in use or being set up. Marking on the ladder's rungs would also not be practical, as it could create confusion and space constraints on the rungs that are meant for safe climbing.