What is the minimum percentage of natural gas required for combustion to take place?

For combustion to occur, a minimum concentration of natural gas, typically consisting of methane, is necessary to form a combustible mixture with air. The lower explosive limit (LEL) for natural gas is around 5% to 15% in the air. However, the industry standard often cites a minimum of approximately 4% to ensure safe and effective combustion.

Therefore, the correct choice of 4% aligns with the typical threshold needed for ignition, meaning that the concentration of natural gas must be at least this percentage for combustion to initiate. At concentrations lower than this minimum, there would be insufficient gas for the combustion process to sustain itself. Additionally, reaching too high a concentration could result in a hazardous situation, but for the purpose of initiating combustion, 4% is the definitive starting point.