What feature is essential for safely using an emergency oxygen system?

The essential feature for safely using an emergency oxygen system is that it must have a secure and functional regulator. The regulator is a critical component that controls the flow of oxygen from the tank to the user, ensuring that the person receives the appropriate amount of oxygen needed in an emergency situation. A secure and functional regulator can prevent leaks, manage pressure effectively, and allow for proper administration of oxygen, which is vital during emergencies, especially when time and air supply are crucial.

While other features, such as portability and alarms, can enhance the usability and functionality of an oxygen system, they are secondary to the need for a reliable regulator. Without a properly functioning regulator, the oxygen delivery could be compromised, making it ineffective in critical moments. Hence, ensuring that the regulator is secure not only facilitates safe usage but also maximizes the efficacy of the emergency oxygen system when it's needed most.