All parts of a crane and its supports must be designed to withstand stresses with a safety factor that is not less than:

The correct answer is that all parts of a crane and its supports must be designed to withstand stresses with a safety factor that is not less than three times the maximum intended load. This standard is in place to ensure the structural integrity and reliability of the crane during operation.

Using a safety factor of three means that the crane is designed to handle loads three times greater than what it would typically encounter. This provides an essential buffer against unexpected stresses that could arise due to operational conditions, material defects, or unforeseen loads. Additionally, cranes often operate in dynamic environments where loads can change rapidly, and incorporating a safety factor of this size helps to mitigate the risk of failure or accidents.

A lower safety factor would not provide adequate assurance of safety, potentially leading to structural failures under normal operating conditions. Therefore, adherence to the safety factor of three is critical in ensuring the safety of operators and those working around the crane, as well as maintaining the longevity of the equipment itself. This requirement aligns with industry standards and regulations, underlining the importance of cautious and effective engineering practices in crane design.