The correct answer is B) detonation arrestor. A detonation arrestor is a large metallic device installed directly in the piping, usually near the vapor hose connection at the dock. It is designed to prevent the passage of a rapidly moving flame through the piping, thus stopping the propagation of a detonation or explosion. This is a key safety feature required by US Coast Guard regulations for cargo transfer operations involving flammable or combustible liquids. The other answer choices are incorrect because a "detonation blocker" is not a standard term, "flame arrestor" is a broader term that encompasses detonation arrestors, and a "flame screen" is a different device used for a different purpose.