Which of the following indicates a safe atmosphere for entry into a confined space?

A safe atmosphere for entry into a confined space is indicated by a minimum of 19.5% oxygen content in the air. This threshold is critical because lower oxygen levels can impair cognitive and physical abilities, leading to potentially dangerous situations. The Occupational Safety and Health Administration (OSHA) and other safety guidelines define 19.5% as the acceptable minimum for safe entry, while 21% is considered the standard atmospheric oxygen level at sea level.

An atmosphere with less than 19.5% oxygen poses a risk for asphyxiation, while a reading above this percentage, up to approximately 23.5%, is still generally safe but can indicate an enriched atmosphere potentially leading to other hazards such as increased flammability or oxidization. Therefore, maintaining oxygen levels above 19.5% is essential for ensuring worker safety within confined spaces.

An oxygen content of exactly 20% is indeed safe, but it does not conform to the established minimum requirement for safety, which is why the focus is on the acceptable threshold rather than a specific value that still falls within the safe range. The other options indicate conditions that are either unsafe or do not meet the necessary criteria for a safe confined space entry.