The mixture of fuel vapor to air that will ignite when subjected to an ignition source is the:

The mixture of fuel vapor to air that will ignite when subjected to an ignition source is the:

• A. Explosive/flammable range
• B. Autoignition range
• C. Flash point
• D. Combustion zone

Answer: (A)

The key idea is the flammable/explosive range—the range of fuel vapor in air that can ignite when an ignition source is present. Within this window, a spark or flame can start combustion; outside it, ignition can’t occur because the mixture is either too lean (not enough fuel) or too rich (not enough oxygen). Autoignition range, by contrast, is about mixtures that ignite on their own at a certain temperature without an external spark. The flash point concerns the temperature at which a liquid begins to emit enough vapor to form an ignitable mixture, not a concentration range in air. The term typically isn’t used to describe the ignitable fuel-air window in the environment.

The key idea is the flammable/explosive range—the range of fuel vapor in air that can ignite when an ignition source is present. Within this window, a spark or flame can start combustion; outside it, ignition can’t occur because the mixture is either too lean (not enough fuel) or too rich (not enough oxygen). Autoignition range, by contrast, is about mixtures that ignite on their own at a certain temperature without an external spark. The flash point concerns the temperature at which a liquid begins to emit enough vapor to form an ignitable mixture, not a concentration range in air. The term typically isn’t used to describe the ignitable fuel-air window in the environment.