What does a trap seal prevent?

A trap seal serves a crucial role in plumbing systems by preventing the escape of sewer gases and odors from the drainage system into the living spaces of a building. This is achieved by the design of the trap, which retains a certain amount of water that creates a barrier. The water seal effectively blocks the passage of gases while allowing wastewater to flow through the drainage system.

This function is vital for maintaining healthy indoor air quality and preventing unpleasant smells that can arise from the sewer system. The other choices, while related to plumbing issues, do not directly describe the primary purpose of a trap seal. For instance, while traps can play a role in preventing backflow, that is not their main function, and they do not prevent water from entering or pressure loss in the system. Thus, the correct emphasis on the trap seal's effectiveness in stopping odor escape highlights its importance in ensuring a safe and comfortable environment.