The primary reason gas does not ignite is due to a lack of the necessary ignition conditions. For a gas to ignite, three key elements must be present: a fuel source, an oxidizer, and a spark or heat source. If any of these elements are missing or insufficient, the gas will not ignite.

In the United States, the most common scenario where gas fails to ignite is when the fuel-air mixture is not within the optimal range for combustion. This range, known as the flammability limit, varies depending on the specific gas. For instance, the flammability limit for natural gas is typically between 5% and 15% in air. If the concentration of gas in the mixture is below the lower flammability limit or above the upper limit, the mixture will not support combustion.

Another common reason for failed ignition is a lack of oxygen. In many cases, the air supply to the combustion chamber is restricted, which can prevent the gas from reaching the optimal flammability range. For example, a clogged air filter in an engine can significantly reduce the oxygen supply, leading to a failure to ignite.

Data from the National Fire Protection Association (NFPA) indicates that approximately 40% of all fire incidents involve flammable gases. This highlights the importance of ensuring that the necessary conditions for ignition are met to prevent accidents and fires.

Furthermore, the presence of impurities in the gas can also hinder ignition. Contaminants such as water, dust, or other chemicals can coat the surfaces of combustion equipment, reducing their efficiency and potentially preventing ignition. According to a study published in the Journal of Loss Prevention in the Process Industries, impurities in gas can lead to a decrease in combustion efficiency of up to 30%.

In summary, the failure of gas to ignite is primarily due to an improper fuel-air mixture, insufficient oxygen supply, or the presence of impurities. Ensuring that these conditions are met is crucial for safe and efficient combustion.