Final answer:
Wells with a vertical depth of at least 240 inches should have a permanent ladder or steps, with variations based on local regulations.
Step-by-step explanation:
Wells with a vertical depth of at least 240 inches (which equates to 20 feet) should have a permanent ladder or steps for safety and accessibility reasons. Going by the rule of thumb mentioned, if we consider a well with a diameter of 8 feet (96 inches), it would need to be 15 diameters deep, which means it would require a vertical depth of 1440 inches (15 x 96 inches) to necessitate a permanent ladder or steps. It's critical to note that actual regulations can vary based on local building codes and safety regulations, and this generalized rule of thumb may differ from official requirements.