What grade must rescue chain assemblies have to ensure safety?

The correct choice emphasizes using a grade 8 or 80 rescue chain assembly, which provides a safety factor of 4 to 1. This is significant for ensuring maximum strength and reliability when performing rescue operations. The grade of a chain indicates its tensile strength, and grade 8 chains are designed to withstand heavy loads under extreme conditions, making them ideal for rescue scenarios where safety is paramount.

A safety factor of 4 to 1 means that the chain can handle four times the load it is rated for, which adds a crucial margin of safety during use. This is particularly important in rescue situations where unexpected forces can occur, and operators must have confidence that their equipment will perform as needed without failure.

The other options present different grades and safety factors that do not provide the same level of assurance. Lower grades or insufficient safety factors may not adequately support the needs of rescue operations, potentially leading to equipment failure and increased risk during rescue attempts.