What is the main safety concern regarding the use of covers on manholes?

The primary safety concern regarding the use of covers on manholes revolves around ensuring that they cannot be opened without tools. This is critical because manholes often contain utilities, cables, and other infrastructure that can pose significant risks to unauthorized individuals, such as the potential for injury or accidents if someone were to access these areas without proper training or safety measures in place.

By designing manhole covers that require tools for opening, municipalities and utility companies can significantly limit unauthorized access, thereby protecting the public from hazardous conditions that exist underground. This design consideration serves as a preventive measure to maintain safety standards and minimize liability from potential accidents.

The other options address related but distinct safety issues. While easy access for unauthorized personnel is a concern, the implementation of tool-requiring covers directly addresses this issue. Potential for falling objects and preventing dust and debris accumulation, while important considerations in their own right, do not directly relate to the overarching goal of limiting access to dangerous utilities and ensuring the safety of individuals in the vicinity.