Characteristics Of Natural Gas Practice Test

What happens to the possibility of combustion when natural gas concentration exceeds 15% in air?

Combustion is more likely Combustion cannot occur because there is not enough air Combustion occurs at the same rate as with lower concentrations Combustion becomes spontaneous

Correct Answer:

Combustion cannot occur because there is not enough air

Explanation:

When a methane‑air mixture is considered, there is a specific flammability window defined by the upper flammable limit. As the fuel concentration climbs toward and beyond this limit, there isn’t enough oxidizer (oxygen) available to sustain a flame. Around methane in air, that upper limit is about 15% by volume. So, when natural gas concentration exceeds this, the mixture is too fuel‑rich and combustion cannot occur under normal conditions because there isn’t enough air to support ignition and flame propagation. The idea that ignition would happen more easily, occur at the same rate, or become spontaneous doesn’t fit with the flammable‑limit concept, which states combustion cannot be sustained once the mixture is above the upper limit.

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