In what scenario is a plumbing trap required?

A plumbing trap is primarily required to prevent sewer gases from escaping into occupied spaces. Traps function by maintaining a small amount of water in a curved section of the pipe, which acts as a barrier. This water seal prevents the gases from the sewage system from entering living areas, thereby protecting the health and safety of the occupants. Without traps, harmful and unpleasant sewer gases could infiltrate buildings, which is a serious hazard.

In contrast, while easy maintenance, reducing water use, and increasing drainage speed are all important considerations in plumbing design, they do not directly address the fundamental purpose of traps in maintaining air quality and safety in residential and commercial buildings.