Ontario Office of the Fire Marshal (OFM) NFPA Technical Rescue (NFPA 1006) Written Practice Exam

Question: 1 / 400

Pulley sheaves should ideally have a diameter of what ratio compared to the rope?

Twice the diameter of the rope

Three times the diameter of the rope

Four times the diameter of the rope

The ideal diameter of pulley sheaves compared to the rope is four times the diameter of the rope. This ratio is crucial because a larger diameter helps reduce the bending stress on the rope as it travels over the sheave. When the diameter of the sheave is adequately larger, it minimizes wear and damage to the rope, extends its lifespan, and maintains its strength and performance during operation.

Using sheaves with a smaller diameter relative to the rope could lead to excessive wear, increased friction, and potential failure of the rope, particularly in a high-load or critical rescue scenario. Therefore, adhering to the four-to-one ratio not only enhances safety but also optimizes the efficiency of the system being used for technical rescue operations.

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Equal to the diameter of the rope

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