Plumbing traps are an essential feature of sanitary drains because they prevent

Plumbing traps (e.g., P-traps) are U-shaped pipe sections that hold water, creating a seal to block sewer gases (e.g., methane, hydrogen sulfide) from entering buildings, per the International Plumbing Code (IPC). Option A (wastewater backflow) is managed by check valves, not traps. Options C and D (water supply contamination) involve cross-connection prevention (e.g., backflow preventers), not traps, which are specific to drain systems. Traps’ primary role is gas containment, making B correct.

Verified Answer from Official Source:B - the backflow of sewer gases

"Plumbing traps are required to prevent the backflow of sewer gases into occupied spaces bymaintaining a water seal in the drain system." (NCIDQ IDPX Study Guide, Section 2: Building Systems)

Explanation from Official Source:The NCIDQ aligns with IPC standards, noting traps as a critical health and safety feature in plumbing design to protect indoor air quality.

Objectives:

Understand plumbing system functions (IDPX Objective 2.9).