What does the flammable range describe?

The flammable range refers specifically to the upper and lower limits of an air/fuel mixture that can ignite and sustain combustion. This range is crucial in understanding fire safety and hazardous materials management because it indicates the concentrations of fuel in the air that can lead to an explosion or fire.

When the concentration of flammable vapor in the air is below the lower limit, the mixture is too "lean" to ignite, while if it exceeds the upper limit, it is too "rich" to support combustion. This concept is vital for safety precautions in environments where flammable materials are handled, stored, or processed, as maintaining concentrations within these limits minimizes the risk of fire and explosion.

The other options do not accurately describe the flammable range; while they address relevant aspects of flammability, they do not pinpoint the specific definition of the range itself, which focuses on the combination of air and fuel concentrations that are capable of igniting.