True or False: LFL and UFL are often used interchangeably with LEL and UEL.

The statement that LFL (Lower Flammable Limit) and UFL (Upper Flammable Limit) are often used interchangeably with LEL (Lower Explosive Limit) and UEL (Upper Explosive Limit) is correct.

Both pairs of terms (LFL with LEL and UFL with UEL) refer to the same concepts in the context of flammable substances and their potential to ignite. The lower flammable limit defines the minimum concentration of a gas or vapor in air that can ignite, while the upper flammable limit defines the maximum concentration at which ignition can occur. When these limits are exceeded, either there is too much of the substance (rich mixture) or too little (lean mixture) for combustion.

Although there can be nuanced differences in definitions and contexts depending on the specific field, in many practical applications, LFL and UFL are indeed often used interchangeably with LEL and UEL. This practice is rooted in the essential meanings behind these limits, which aim to quantify the concentration range in which a fuel and air will support combustion.