Final answer:
The FiO2 achievable with a non-rebreather mask is 80-100%, as it is designed to deliver high levels of oxygen from a reservoir bag.
Step-by-step explanation:
The FiO2 (fraction of inspired oxygen) achievable with a reservoir bag mask, also known as a non-rebreather mask, is typically between 80-100%. This type of mask allows for higher levels of oxygen to be delivered as it has a reservoir that contains pure oxygen, which the patient inhales. The high-flow system prevents significant rebreathing of expired air because the reservoir bag attached to an oxygen source ensures that oxygen is only inspired, and the exhalation ports allow carbon dioxide to escape.