Question 275General Subjects - 1st Asst/Chief

The correct answer is D. When the marine inspector determines that a hydrostatic test is warranted for a fired thermal fluid heater, the system's heating medium fluid can be used as the hydrostatic test medium, rather than requiring the system to be completely drained and refilled with water. This is in accordance with 46 CFR regulations, which allow the use of the existing heating medium fluid for the hydrostatic test, provided it is compatible with the system components. The other answer choices are incorrect because they either require the use of compressed air (A) or water (B and C) as the test medium, which is not necessary or required by the regulations for this type of system.