What is the minimum percentage of oxygen that must be present in a confined space before entering?

In a confined space, the minimum percentage of oxygen that must be present before entering is 19.5%. This level is crucial for ensuring the safety of individuals entering such environments, as normal atmospheric air contains approximately 21% oxygen.

When the oxygen concentration drops below 19.5%, it is considered an unsafe level, as it can lead to hypoxia, which is a condition where the body does not get enough oxygen. This presents serious health risks, including confusion, unconsciousness, and even death.

The other percentages listed do not provide a safe threshold for oxygen levels in confined spaces. Levels below 19.5% do not meet the basic requirements for safe entry into such areas, making it essential to monitor oxygen levels before attempting to perform any work or activity within them.