HAZMAT Technician Practice Exam

The upper flammable limit being higher than the lower limit is indeed a correct statement regarding flammable limits. In the context of flammable substances, these limits define the concentration range of vapors in the air that can ignite and sustain a fire. The lower flammable limit (LFL) is the minimum concentration of the vapor required for combustion to occur, meaning that below this concentration, a mixture is too "lean" to ignite. On the other hand, the upper flammable limit (UFL) is the highest concentration of the vapor in the air that will allow combustion. If the concentration exceeds this upper limit, the mixture becomes too "rich" to ignite due to insufficient oxygen available for combustion.

Understanding these limits is crucial for safety in handling and storing flammable materials, as working within these boundaries can help prevent fires and explosions. The specific values of the LFL and UFL can vary between different substances, demonstrating that the limits are not constant across all materials, which counters one of the other choices.