Which of the following is NOT a proper action when using extension ladders?

Using a ladder on uneven ground is not a proper action because it poses significant safety risks. Extension ladders require a stable and level surface to ensure they do not slip or tip while in use. Uneven ground can compromise the ladder's stability and increase the likelihood of accidents or falls.

The other actions mentioned are essential for safe ladder use. Checking the ladder before use helps identify any damage or wear that could lead to failure. Working in pairs to stabilize the ladder adds an extra layer of safety, ensuring that it remains secure during operations. Ensuring adequate overlap between sections is crucial for maintaining the ladder's structural integrity and preventing it from collapsing while in use. All of these points emphasize the importance of safety and proper practices when using extension ladders.