What is the upper threshold for oxygen concentration in a confined space before it becomes hazardous?

The upper threshold for oxygen concentration in a confined space before it becomes considered hazardous is generally recognized as 23.5%. In an atmosphere containing more than this concentration of oxygen, there is an increased risk of fire and explosion. Elevated oxygen levels can make materials that are normally not combustible catch fire more easily, creating significant safety hazards.

Understanding the acceptable limits of oxygen concentration is crucial in industrial hygiene. The normal atmospheric concentration of oxygen is about 20.9%. While a slight increase can improve worker performance and safety in certain contexts, concentrations above 23.5% are indicative of an environment that could promote rapid combustion.

In confined spaces where oxygen can accumulate, maintaining a balance is vital for safety. Thus, 23.5% serves as a crucial threshold limit for oxygen concentrations, beyond which immediate precautions and potential evacuations may be necessary to prevent dangerous fire hazards.