Cooperative Personnel Services Firefighter (CPS) Practice Exam 2026 – The All-in-One Guide to Master Your Firefighter Exam Success!

The correct answer indicates that the Upper Flammable Limit (UFL) increases while the Lower Flammable Limit (LFL) remains mostly unaffected as temperature increases.

Understanding how temperature impacts flammability limits is crucial in fire science. The UFL is the highest concentration of a combustible vapor in air that can ignite. As temperature increases, the vapor pressure of a flammable substance increases, allowing it to disperse more easily in the air which raises its UFL. Higher temperatures lead to a greater amount of fuel providing a richer mix which can ignite but only within certain limits.

On the other hand, the LFL is the lowest concentration of a combustible vapor that can ignite. This limit typically remains relatively stable with temperature changes. While it's influenced by various factors like pressure and the specific characteristics of the material, it generally does not decrease appreciably with temperature rise.

Thus, this understanding supports the conclusion that while UFL increases with temperature, LFL does not experience significant changes, aligning perfectly with the stated answer.