An unsafe condition that riggers should be aware of when dealing with a multi part load block is:

When dealing with a multi-part load block, an important unsafe condition that riggers must remain vigilant about is the potential for twisting in the multi-part lines. Twisting can lead to various operational hazards such as unexpected load movement, line failure, or equipment damage. When the lines twist, it increases the complexity of the load dynamics, which can result in an uneven distribution of weight or unintended movements that can compromise safety during lifting operations.

Being aware of twists allows riggers to take preventative measures, such as ensuring proper rigging techniques are implemented and making adjustments to lines to keep them untwisted. This understanding is crucial for maintaining the integrity of the rigging system and ensuring safe operational practices, especially in dynamic environments where loads might shift or move.

The other options, while relevant to rigging, do not specifically denote a direct unsafe condition associated with multi-part load blocks. Decreased lifting capacity relates generally to load limits but does not pertain to the immediate risks presented by twisted lines. Static load refers to loads that remain stationary and is not inherently unsafe unless other factors contribute to risk. Added crane gross capacity describes the overall strength of the crane rather than a concern related to the rigging itself.