Manhole covers that are what diameter or more should be secured to prevent unauthorized openings?

The size of manhole covers is critical in determining their potential risk for unauthorized access or safety hazards. Covers that have a larger diameter, such as 20 inches or more, are often deemed significant enough to pose a danger if left unsecured.

Typically, manhole covers that are 20 inches in diameter or larger are targeted for securing. This is because these sizes provide enough room for an individual to gain entry, which could lead to safety issues as well as theft or vandalism. By ensuring these larger covers are secured, it helps to protect both public safety and prevent unauthorized access to potentially dangerous infrastructure such as utility access points.

Thus, choosing 20 inches as the minimum threshold reflects a standard measure within the industry for safety and security procedures. Securing covers with diameters smaller than this might not address the same level of risk, as they do not allow for a person to pass through as readily while still protecting the infrastructure below.