What is the maximum height for used lumber to be stacked manually after removing all nails?

The correct choice presents the maximum height for used lumber to be stacked manually after all nails have been removed as 16 feet. This height is based on safety regulations and best practices within the construction industry to ensure that lumber can be handled securely without being at risk of toppling over or creating a hazard for workers. When stacks exceed this height, the risk of instability increases, making it more challenging to manage the lumber safely.

In the context of the construction environment, keeping stacks at a manageable height not only promotes safety for those handling and accessing the lumber, but also allows for easier identification and retrieval of materials. Proper stacking techniques, including the removal of nails, further mitigate any potential injuries or accidents that can occur from handling used lumber. Therefore, the guideline to limit manual stacking height to 16 feet reflects a commitment to maintaining a safe working environment for construction personnel.