Which item is NOT typically considered a double barrier protection factor?

• A. Hull penetrations above waterline
• B. O2
• C. Sea connected systems
• D. Hazardous gases/liquids

Answer: (A)

Double barrier protection relies on two independent layers that prevent hazards from reaching personnel or the environment. The hull is a protective shell, and anything that creates an opening or breach—like hull penetrations above the waterline—acts as a vulnerability rather than a protective barrier. It undermines the double-barrier concept by providing a direct path for hazards to enter or escape, so it isn’t a protective factor.

In contrast, the other items represent parts of the safety system that help maintain two effective barriers. Oxygen levels support a safe breathing atmosphere in enclosed spaces, contributing to the first line of defense. Sea-connected systems provide redundancy and alternate pathways to maintain safe conditions or containment, supporting the integrity of the barriers. Hazardous gases or liquids require proper containment and separation, which are fundamental to keeping hazards isolated from crew spaces.