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What Is the Difference Between %LEL and %VOL When Measuring Flammable Gas?

When it comes to handling and monitoring flammable gases, safety is of paramount importance. Accurate measurement and understanding of gas concentrations are crucial to maintaining a safe working environment. Two common units used in the field of gas detection are %LEL (Lower Explosive Limit) and %VOL (Volume Percent). In this post, we will explore the key differences between %LEL and %VOL and their significance in assessing flammable gas hazards.


Understanding %LEL:

%LEL, or Lower Explosive Limit, refers to the minimum concentration of a flammable gas or vapour in the air that can ignite and sustain combustion. It is expressed as a percentage of the gas's lower explosive limit. The lower explosive limit is the minimum concentration required for a mixture of gas and air to create an explosive atmosphere.

Understanding %VOL:

%VOL, or Volume Percent, represents the concentration of a gas in the air as a percentage of the total volume. It indicates the proportion of gas present in the air, regardless of its flammability. %VOL is a measure of the gas concentration in relation to the total volume of the gas-air mixture.

Key Differences and Significance:

The fundamental difference between %LEL and %VOL lies in the interpretation of the measurements. While %LEL specifically focuses on the flammability of a gas, %VOL represents the overall concentration, regardless of flammability.

%LEL is particularly useful for assessing the risk of an explosive atmosphere. It helps in determining the safe operating limits for various gases in hazardous environments. Gas detectors calibrated in %LEL allow for quick identification of potentially dangerous concentrations, as they are directly related to the flammability properties of the gas being monitored.

On the other hand, %VOL is more suitable for general gas detection applications where the focus is on identifying the presence or absence of a specific gas. 

It is important to note that %LEL and %VOL are not interchangeable. The %LEL value for a gas is typically specific to that particular gas, whereas %VOL can be used to measure the concentration of any gas in a given air mixture.


In the realm of flammable gas detection, understanding the difference between %LEL and %VOL is crucial for maintaining a safe working environment. %LEL is a measure of flammability, indicating the minimum concentration at which a gas can ignite, while %VOL represents the concentration of a gas in relation to the total volume, regardless of its flammability.

By utilising both %LEL and %VOL measurements, gas detection professionals can accurately assess the risk of explosion and detect the presence of specific gases. This knowledge enables them to implement appropriate safety measures, monitor industrial processes, and protect lives and property from the hazards associated with flammable gases.