Propane is flammable in air within what range?

• A. Approximately 1.0% to 4.0%
• B. Approximately 2.1% to 9.6%
• C. Approximately 0.5% to 2.0%
• D. Approximately 10% to 20%

Answer: (B)

Propane’s flammable range is defined by the concentrations in air that can ignite when an ignition source is present. For propane, that range is about 2.1% to 9.6% by volume in air. Within this interval, a spark, flame, or hot surface can ignite the vapor–air mixture. If the concentration is below roughly 2.1%, it’s too lean to ignite; if it’s above roughly 9.6%, it’s too rich for combustion to sustain. So the range 2.1% to 9.6% best fits how propane behaves in air. In practice, leaks can accumulate in low areas (propane is heavier than air), so proper ventilation and leak detection are important.