Upper Explosive Limit (UEL)

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Definition - What does Upper Explosive Limit (UEL) mean?

The upper explosive limit (UEL) is the highest concentration of gas, vapor or mist in the air at which an explosion may arise if the substance is ignited. A material is, therefore, most likely to explode if its concentrations are within the lower and upper limits. Concentrations of gases or vapors in the air that are below the lower explosive limit or above the upper explosive limit are considered to be non-explosive. Knowing the upper and lower explosive limits are important for safety considerations.

The upper explosive limit may also be known as the upper flammability limit.

Corrosionpedia explains Upper Explosive Limit (UEL)

For a fire or explosion to occur, two basic conditions must be met:

  1. The fuel (flammable gas) and oxygen must be mixed in certain proportions, and
  2. The fuel-oxygen mixture must come into contact with an ignition source (flame, spark, hot object, etc.)

To support combustion, there must be a minimum concentration of flammable gas in the air. This concentration is referred to as the lower explosive gas limit. As the gas concentration increases above the lower explosive limit, the mixture remains explosive up to a threshold called the upper explosive limit. Above the upper explosive limit concentration, the mixture will no longer be explosive, as it is considered to be “too rich” to burn.

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