What could happen if a PV breaker does not refill with liquid before operations resume?

When a pressure-vacuum (PV) breaker does not refill with liquid before operations resume, the most significant risk is that pressure build-up could occur, potentially leading to failure. The PV breaker is designed to prevent excessive pressure from building up in the tank during the transfer of liquid, ensuring that it can manage both vapor and liquid pressure changes safely.

If the breaker hasn't refilled, it may not function correctly, and the system could experience an increase in pressure as tanks are filled or emptied. This excessive pressure can compromise the structural integrity of the tank, risking rupture or explosion, which poses serious safety hazards and could result in environmental damage as well.

Addressing the other options, while a tank collapsing can be dangerous, it generally occurs due to improper structural design or integrity rather than just the PV breaker misfunctioning. Fuel leakage can happen in various situations, but it is not as directly related to the status of the PV breaker. The effectiveness of tank cleanout does not directly relate to the PV breaker not being refilled; cleanout processes are separate and hinge more on procedures and equipment for managing tank residues.