What is the minimum percentage of O2 for entry into a confined space without a Self Contained Breathing Apparatus?

The minimum percentage of oxygen for safe entry into a confined space without requiring a Self Contained Breathing Apparatus is 19.5%. This is based on safety standards and regulations that dictate the optimal range of oxygen concentration necessary to maintain safe breathing conditions. Normal atmospheric air contains around 20.9% oxygen, and levels at or above 19.5% are generally considered safe for workers, as they provide sufficient oxygen for normal respiratory function while minimizing the risk of suffocation or hypoxia that could occur in environments with lower oxygen levels.

When oxygen levels drop below 19.5%, the atmosphere is considered hazardous and can lead to potential health risks, making it imperative to use appropriate breathing apparatuses or implement other safety measures. Therefore, the correct choice reflects the established safety threshold for confined space entry.