Which of the following can cause two blocking?

Two blocking occurs when the hook block is pulled up against the boom point, causing a dangerous situation that can lead to equipment damage or accidents. Understanding the potential causes of two blocking is crucial for safe crane operation.

The correct answer identifies that both hoisting and extending the boom can cause two blocking. When hoisting, if the load is lifted while simultaneously trying to extend the boom, the hook block may rise too close to or even come into contact with the boom’s top. This can lead to two blocking due to the conflicting actions of lengthening the boom while raising a load.

Extending the boom alone can also lead to two blocking because as the boom is extended, the effective height increases and can bring the hook block into a position where it can touch the boom.

Recognizing that both actions can contribute to this hazard is important for crane operators, as it highlights the need for caution and awareness of how different crane functions interact with one another. Operators must implement techniques to prevent two blocking, such as using anti-two blocking devices or following proper signaling protocols when performing these actions.