What are the Lower Flammable Limit (LFL) and Upper Flammable Limit (UFL)?

The Lower Flammable Limit (LFL) and Upper Flammable Limit (UFL) are critical concepts in understanding flammability and safety management for various substances. The LFL is defined as the lowest concentration of a combustible substance in air that can ignite and support combustion when an ignition source is present. This means that if the concentration is below this level, there is not enough fuel to sustain a flame, making it safe from ignition.

In contrast, the UFL indicates the highest concentration of that substance in air that can still ignite. Beyond this limit, there is too much fuel present, which prevents the formation of a flammable mixture with air. Therefore, this choice accurately reflects the fundamental principles of combustion; understanding these limits is essential for maintaining a safe working environment, especially when dealing with hazardous materials, such as asbestos and other chemicals.

The other provided options misconstrue the definitions or suggest that the two limits are not relevant to each other, which is not consistent with established safety protocols and scientific understanding of flammable materials. Recognizing both the LFL and UFL allows for effective risk assessment and management in environments where flammable substances are present.