Material and debris must not be placed within how many inches of an open trench in which a man can work?

The correct answer is that material and debris must not be placed within 18 inches of an open trench in which a man can work. This regulation is critical for ensuring the safety of personnel who are working near the edge of a trench. If materials and debris are stacked too close to the trench, they can pose a risk of falling into the trench, which could lead to serious injuries or accidents. Maintaining a safe distance helps create a clear working area, reduces the potential for cave-ins, and allows for easy access to emergency situations.

Distances such as 12, 24, or 30 inches would not align with safety protocols that have been established for trench work, where 18 inches is considered the minimum safe distance. This standard helps to ensure that there is adequate space to safely perform work tasks without the added risk of debris or materials causing hazards in the work area.