4th Class Power Engineering 4B7 Practice Exam

Stack height is about how far the combustion products can mix with ambient air before reaching the ground. A taller stack releases the plume higher, where there’s more air, more turbulence, and often steadier winds, so the pollutants get diluted more effectively. This dilution lowers ground-level concentrations and reduces the potential exposure for people and environments nearby, which is a key safety consideration and helps meet air-quality standards. If the stack is too short, pollutants stay closer to the ground, leading to higher concentrations downwind and greater exposure risk. The stack height doesn’t determine boiler pressure or fuel flow—the boiler design and fuel system control those—and there’s no effect to ignore: height truly changes how the emissions disperse after they’re released.