What does the upper explosive limit of a hydrocarbon refer to?

The upper explosive limit (UEL) of a hydrocarbon is the maximum concentration of vapor in air at which the mixture can ignite. Beyond this point, there isn't enough oxygen present to support combustion, so the mixture becomes too rich in fuel. Understanding the UEL is crucial for safety in handling flammable substances, as it helps to identify conditions that can lead to explosive hazards. When concentrations exceed the UEL, even though there may be sufficient fuel, the lack of oxygen prevents ignition, making it safe under certain conditions. Thus, recognizing the UEL allows for better risk management and preventive measures in environments where hydrocarbons are present.