According to 46 CFR regulations pertaining to periodic tests and inspections as related to fired thermal fluid heaters, regarding hydrostatic tests, what statement is true?

Correct Answer: Option D — When the marine inspector determines that a hydrostatic test is warranted, the fired thermal fluid heater heating medium fluid can be used as a hydrostatic test medium.

For fired thermal fluid heaters, 46 CFR allows the use of the system's own heating medium fluid for hydrostatic testing. This avoids the risk of water contamination or the complex process of cleaning and drying the system, which could otherwise lead to corrosion or operational failures upon system restart.