What is the minimum oxygen level required before entering a transformer?

The minimum oxygen level required before entering a transformer is 23.5% by volume. This is because a concentration of oxygen at or above this level is necessary to ensure a safe working environment, particularly to prevent the risk of asphyxiation and to support human life effectively. In confined spaces such as transformers, oxygen levels below this threshold can create hazardous conditions where workers may experience dizziness, a reduced ability to think clearly, or even loss of consciousness due to insufficient oxygen supply.

A concentration of 21% by volume is considered normal atmospheric air, but entering a confined space should account for potential displacement of oxygen by other gases or vapors, which can occur during maintenance or operational tasks. Safety regulations typically specify a higher minimum threshold to ensure that there is no risk posed by such displacements. Thus, while 19.5% is the standard level for defining oxygen deficiency in many safety protocols, the specific level of 23.5% is established as a safer working condition in the context of transformer entry.