LFL and UFL are often used interchangeably with Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL).

LFL and UFL are often used interchangeably with Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL).

• A. True
• B. False
• C. Not always true
• D. Not applicable

Answer: (A)

Two terms describe the same safety thresholds for a gas–air mix: the lower limit marks the faintest concentration that can ignite, and the upper limit marks the concentration above which flame cannot propagate. The labels differ only in wording: lower/upper explosive limit versus lower/upper flammable limit. For a given substance, the numerical values are identical, so LFL and UFL are commonly used interchangeably with LEL and UEL in safety contexts. This makes the statement true, since the two naming schemes refer to the same ignition range even though the terms differ.

Two terms describe the same safety thresholds for a gas–air mix: the lower limit marks the faintest concentration that can ignite, and the upper limit marks the concentration above which flame cannot propagate. The labels differ only in wording: lower/upper explosive limit versus lower/upper flammable limit. For a given substance, the numerical values are identical, so LFL and UFL are commonly used interchangeably with LEL and UEL in safety contexts. This makes the statement true, since the two naming schemes refer to the same ignition range even though the terms differ.