Final answer:
An operator visually checks a particular portion of the delivery-hose assembly when there is a suspicion of contamination, damage, or a blockage.
Step-by-step explanation:
An operator is required to visually check a particular portion of the delivery-hose assembly when there is a suspicion of contamination, damage, or a blockage. This visual inspection is crucial to ensure the safe and efficient delivery of fluids. For example, if there is a suspicion of contamination, the operator should check for any discoloration or unusual particles in the hose assembly.