Detention time calculation requires consistent units for volume and flow.

Detention time calculation requires consistent units for volume and flow.

• A. Only in gallons
• B. Only in liters
• C. Yes
• D. No

Answer: (C)

Detention time is found by dividing the volume by the flow rate, so the units must cancel to give a time. You can use any consistent pair of units for volume and flow—gallons with gallons per hour, or cubic meters with cubic meters per day, for example—as long as you convert so they match. If the units aren’t aligned, the calculation won’t yield a valid time without converting. So consistency is required. Limiting you to only one unit (gallons or liters) isn’t correct, and saying there’s no unit requirement isn’t right either.

Detention time is found by dividing the volume by the flow rate, so the units must cancel to give a time. You can use any consistent pair of units for volume and flow—gallons with gallons per hour, or cubic meters with cubic meters per day, for example—as long as you convert so they match. If the units aren’t aligned, the calculation won’t yield a valid time without converting. So consistency is required. Limiting you to only one unit (gallons or liters) isn’t correct, and saying there’s no unit requirement isn’t right either.