What is characterized as an unplanned roof or rib fall in active workings?

An unplanned roof or rib fall in active workings is characterized as an accident that impedes passage. This type of event poses immediate safety risks to miners and disrupts operations by blocking access routes or creating hazardous conditions.

In mining operations, managing ground stability is crucial for safety and productivity. When a roof or rib fall occurs unexpectedly, it means that the structural integrity of the mine has been compromised, which can lead to injury and poses a significant threat to the workers in the area. Such incidents require immediate attention to ensure the safety of personnel and to evaluate and rectify the situation to prevent further falls.

The other options do not accurately describe the nature of an unplanned roof or rib fall. An increase in operational efficiency or a scheduled mine inspection reflects proactive and planned activities that enhance productivity and safety, while a normal geological occurrence typically refers to predictable natural events that do not disrupt operations in an unplanned manner.