The flammable-explosive range describes the vapor concentration range in air that will ignite. Which option best completes this statement?

• A. Lower Explosive Limit
• B. Upper Flammable Limit
• C. Flash Point
• D. Flammable-Explosive Range

Answer: (D)

Ignition depends on having the right vapor concentration in air—the mixture must be neither too lean nor too rich. The window where ignition can occur spans from the lower explosive limit up to the upper explosive limit. That full range is what the term Flammable-Explosive Range describes, because it covers the entire concentration interval that can ignite. The lower boundary is the minimum concentration needed to ignite, and the upper boundary is the maximum; outside this range, ignition isn’t possible. The other options refer to just one boundary (Lower Explosive Limit), the other boundary (Upper Flammable Limit), or a related concept (Flash Point, which is temperature-related, not concentration range).