Final answer:
The rule for the minimum distance a ladder must extend above a trench or excavation is usually at least 3 feet, which is guided by safety regulations for safe access.
Step-by-step explanation:
The minimum distance that a ladder should extend above the top of a trench or excavation is typically governed by occupational safety regulations, which often specify that ladders must extend at least 3 feet (about 0.9 meters) beyond the top edge. This is to ensure that workers have a safe means of egress that is easy to grasp when ascending and descending. In practice, this might be encompassed by specific local or national regulations, and it is always important to consult the relevant safety codes for the most accurate requirements.