An eductor is used to vapor free a tank. How tall does the exhaust need to be?

An eductor is used to vapor free a tank. How tall does the exhaust need to be?

• A. 6 feet
• B. 9 feet
• C. 12 feet
• D. 15 feet

Answer: (C)

The main idea is to vent the vaporized air high enough so the plume doesn’t come back into the work area or into openings like doors, windows, or intakes. When an eductor pulls vapor out of a tank, you want the exhaust to rise and mix with the surrounding air rather than hug the ground where it can be drawn back by nearby air currents or be encountered by operators. Placing the exhaust at a sufficient height reduces the chance that the vapor will be recirculated into the workspace, re-enter the tank through openings, or linger in the breathing zone. It also promotes better dilution of the vapor with ambient air as it disperses outdoors or into a vented area. While a taller exhaust can mean more piping and cost, the safety benefit is clear: higher exhaust improves dispersion and reduces re-entrainment risk, which is why the recommended height is chosen as tall enough to achieve that safety goal.

The main idea is to vent the vaporized air high enough so the plume doesn’t come back into the work area or into openings like doors, windows, or intakes. When an eductor pulls vapor out of a tank, you want the exhaust to rise and mix with the surrounding air rather than hug the ground where it can be drawn back by nearby air currents or be encountered by operators.

Placing the exhaust at a sufficient height reduces the chance that the vapor will be recirculated into the workspace, re-enter the tank through openings, or linger in the breathing zone. It also promotes better dilution of the vapor with ambient air as it disperses outdoors or into a vented area. While a taller exhaust can mean more piping and cost, the safety benefit is clear: higher exhaust improves dispersion and reduces re-entrainment risk, which is why the recommended height is chosen as tall enough to achieve that safety goal.