What is the minimum liquid seal required for fixture traps?

• A. 1 inch
• B. 2 inches
• C. 3 inches
• D. 5 inches

Answer: (B)

The minimum liquid seal required for fixture traps is established to ensure that a proper barrier is maintained to prevent sewer gases from entering habitable spaces. A liquid seal of 2 inches is typically required for most plumbing fixtures, which helps to create an effective barrier to backflow and ensures that the trap can properly hold enough water to fulfill its function.

In practice, this 2-inch seal effectively balances the need for preventing gas escape while also accommodating pressure changes caused by fixtures being used or emptied, allowing for ample drainage without compromising the trap's water seal. A smaller seal could lead to sewer gas entering the living area, while a larger seal isn't usually necessary and can complicate drains without providing additional benefits. Thus, 2 inches is recognized as the optimal minimum height for effective trap function.