The allowable free-standing height of a specific tower crane is specified as 50 m with a maximum out-of-plumb tolerance of 1:500. If the crane mast is measured to be 100 mm out of plumb at a height of 40 m, what action is required?

Question: The allowable free-standing height of a specific tower crane is specified as 50 m with a maximum out-of-plumb tolerance of 1:500. If the crane mast is measured to be 100 mm out of plumb at a height of 40 m, what action is required?

Answer options: ✅ Immediately cease operations and re-plumb the mast, as this exceeds the allowable tolerance.

• Continue operation, as the tolerance applies only at the maximum free-standing height of 50 m.
• Reduce the crane's lifting capacity by 20% until the mast is plumbed.
• Install additional guy wires to compensate for the deviation.

Correct answer: Immediately cease operations and re-plumb the mast, as this exceeds the allowable tolerance.

Explanation: The out-of-plumb tolerance of 1:500 means for every 500 units of height, the deviation can be 1 unit. At 40 m (40,000 mm), the maximum allowable deviation is 40,000 mm / 500 = 80 mm. Since the mast is 100 mm out of plumb, it exceeds the limit, requiring immediate cessation of operations and rectification, according to CSA Z248, to maintain structural integrity.