Below the lower explosive limit (LEL), which statement about the gas-air mixture is correct?

Below the lower explosive limit (LEL), which statement about the gas-air mixture is correct?

• A. There is not enough fuel to initiate or continue an explosion
• B. The mixture will ignite at any ignition source
• C. There is excessive oxygen causing rapid combustion
• D. The vapor is heavier than air

Answer: (A)

The main idea here is flammability limits: a fuel-air mixture must have a concentration within a certain range to support flame propagation and explosion. The lower explosive limit marks the minimum fuel concentration needed for combustion. Below that limit, the mixture is too lean—there aren’t enough fuel molecules to sustain a flame or an explosion even if an ignition source is present. You might see a brief flare, but it won’t continue or propagate. The other statements don’t fit because a lean mixture below the lower limit won’t reliably ignite and sustain burning, oxygen level isn’t about the lower limit (air is already enough for many fuels), and the fact that a vapor may be heavier than air doesn’t determine flammability range or ignition behavior.

The main idea here is flammability limits: a fuel-air mixture must have a concentration within a certain range to support flame propagation and explosion. The lower explosive limit marks the minimum fuel concentration needed for combustion.

Below that limit, the mixture is too lean—there aren’t enough fuel molecules to sustain a flame or an explosion even if an ignition source is present. You might see a brief flare, but it won’t continue or propagate.

The other statements don’t fit because a lean mixture below the lower limit won’t reliably ignite and sustain burning, oxygen level isn’t about the lower limit (air is already enough for many fuels), and the fact that a vapor may be heavier than air doesn’t determine flammability range or ignition behavior.