Before entering an enclosed space, what must be tested in the atmosphere?

The requirement to test for oxygen deficiency before entering an enclosed space is vital for ensuring the safety of individuals in that environment. Oxygen is essential for human survival, and if the oxygen level falls below the safe threshold (typically below 19.5% in workplace safety standards), it can lead to unconsciousness or even death. Testing for oxygen deficiency helps to identify potentially life-threatening conditions before entry, allowing for necessary precautions or ventilations to be taken to ensure a safe atmosphere.

While it is also important to monitor for carbon dioxide levels, temperature, and radioactivity in various settings, those factors are secondary in the immediate context of entering confined spaces. Oxygen levels must be prioritized as a fundamental measure of safety when assessing the atmospheric conditions of an enclosed space.