What FiO2 percentage is delivered by a non-rebreather mask in emergencies?

A non-rebreather mask is designed to deliver a high concentration of oxygen to patients who are experiencing severe respiratory distress or hypoxia. This mask can provide an FiO2 (fraction of inspired oxygen) percentage that typically ranges from 60% to nearly 100%.

The setup of the non-rebreather mask includes a reservoir bag that is filled with pure oxygen. As the patient inhales, they draw oxygen from both the bag and the mask itself, minimizing the air dilution from the surrounding atmosphere. During emergencies, such as situations requiring immediate oxygen therapy, the non-rebreather mask is capable of reaching FiO2 levels that approach 100% when properly fitted and when the reservoir bag remains inflated.

In contrast, the other options either underestimate the potential FiO2 percentage or do not accurately describe the range typically delivered by a non-rebreather mask, thus reinforcing why the answer that encompasses the full range of 21-100% is appropriate in acknowledging the mask's effectiveness in emergencies.