Which initial step is required for using the portable oxygen?

In the context of using portable oxygen in an aircraft emergency situation, ensuring oxygen flow is active is a critical initial step. It is essential to verify that the oxygen system is functioning properly before assisting any passenger. If the oxygen flow is not activated, then even if the mask is fitted securely, it will not provide the intended support.

Starting with the activation of the oxygen flow allows the responder to be assured that the equipment is ready for use, which is paramount in an emergency where every second counts. Once oxygen flow is confirmed to be active, the subsequent steps, such as fitting the mask and instructing passengers, can proceed effectively.