Before entering any space that has been sealed, its oxygen level should be tested. What level of oxygen in the space is equal to fresh air?

Correct Answer: Option C — 20.8%

Fresh air contains approximately 20.8% oxygen by volume. Any deviation from this level in a confined space indicates either oxygen displacement by other gases or consumption by chemical processes, both of which pose significant risks to personnel. Testing for this level is a mandatory safety requirement before entry.