How many masks are attached to a Single Outlet POB?

A Single Outlet Portable Oxygen Breathing (POB) system is designed to deliver oxygen to one user at a time. Therefore, it is equipped with only one mask that is intended for the individual who needs supplemental oxygen. This design allows for focused delivery of oxygen and is practical for emergency situations where a single person requires it.

Having more than one mask, as suggested in some of the other choices, would complicate its use and go against the design purpose of a Single Outlet POB. Each mask in such a system is meant for clarity of purpose, ensuring that the breathing apparatus is effective and efficient in providing oxygen to a single individual as required in emergencies.