Final answer:
The required minimum clear distance between the side rails of all portable ladders is 12 inches, an important safety measure for stable and secure ladder use.
Step-by-step explanation:
The minimum clear distance between side rails for all portable ladders is 12 inches. It is important to adhere to safety regulations when using ladders in any work environment. The specification of the minimum distance helps ensure stability and safe use of the ladder. This distance allows for sufficient space for the safe ascent and descent, as well as the necessary grip and foot placement required when using a ladder.