Which of the following shall be used to isolate fire hydrant valves on a crude oil tanker from the crude oil washing system?

Correct Answer: Option D — spade blanks

Spade blanks provide a positive, physical barrier required by 46 CFR to ensure complete isolation between the crude oil washing (COW) system and fire main piping. This prevents cross-contamination and ensures that fire-fighting water pressure is not compromised by or introduced into the cargo system during operations.