G2 Gas Fitter Practice Exam 2025 - Free Gas Fitter Practice Questions and Study Guide

When a natural gas flame produces more than 10% carbon dioxide, it indicates that the combustion process is likely incomplete. This situation arises from insufficient oxygen being available for the complete combustion of the gas. As a result, carbon monoxide can form alongside carbon dioxide. Carbon monoxide is a colorless, odorless gas that is produced when carbon-containing fuels do not burn fully; thus, its presence poses safety risks and health hazards.

In a properly adjusted flame, the ideal combustion would yield primarily carbon dioxide and water vapor when enough oxygen is present. However, when carbon dioxide levels exceed 10%, it suggests that some carbon is not combusting entirely, leading to the production of carbon monoxide, which is toxic.

The other options do not directly relate to the increase in carbon dioxide: the production of water vapor would remain consistent unless combustion is grossly impaired, excess oxygen is typically reduced rather than used, and heat output may vary but does not directly correlate with high carbon dioxide levels as indicated by this combustion scenario. Therefore, the presence of elevated carbon dioxide levels notably increases the risk of carbon monoxide production.