National Commission for the Certification of Crane Operators (NCCCO) Mobile Crane Practice Exam

During crane operations, what does the term "two-blocking" refer to?

1. A lifting motion exceeding specifications

2. Cable snagging

3. Contact between the hook and the boom

4. Improper signal communication

The correct answer is: Contact between the hook and the boom

The term "two-blocking" specifically refers to the situation where the hook and the boom come into contact with each other during crane operations. This can occur when the crane is lifted too high, causing the hook to move upwards and collide with the upper part of the boom. This condition can pose serious safety risks as it can damage the crane equipment or lead to a potential failure of the lifting operation. Understanding this concept is crucial for crane operators and riggers. It emphasizes the importance of monitoring lift heights and ensuring that operational practices are in line with the crane's specifications and safety guidelines. Proper training and communication among the crew can help prevent two-blocking incidents. While the other options relate to potential hazards or operational issues, they do not capture the specific mechanical interaction that defines two-blocking. For example, exceeding lifting specifications or improper signal communication involves different aspects of crane operation that are critical but do not relate directly to the physical contact between the hook and the boom.