Why must the safety chains (or cables) between a converter dolly and the trailer ahead be inspected and properly secured?

Safety chains (or cables) provide a critical backup connection between the converter dolly's drawbar and the trailer ahead. If the pintle hook were to come open or fail, the chains keep the dolly and the trailer it carries from breaking completely away from the combination, helping the driver bring things to a controlled stop rather than losing a trailer at speed. During inspection the driver checks that the chains are not worn, cracked, or stretched, and that they are correctly attached with the proper amount of slack — enough to allow turning but not so much that they drag or fail to hold. Damaged or improperly secured safety chains must be corrected before the combination is driven.