Turbocharge Your Skills: Ace the G2 Gas Fitter Exam 2025 – Ignite Your Career Potential!

The correct choice is the raw gas nozzle mix burner type, which is associated with the greatest risk of flashback. Flashback occurs when the flame travels back into the burner or gas supply line, often due to improper mixing of the gas and air or an insufficient supply of air.

Raw gas nozzle mix burners operate by introducing raw gas into the combustion chamber, where it mixes with air to produce a flame. This type of burner can create conditions conducive to flashback, particularly if the gas-air mixing is not optimal. If the gas concentration at the nozzle is too high or if there is turbulence in the combustion zone, the flame can propagate back into the nozzle.

The other burner types listed, such as mechanical air premix, atmospheric, and high-efficiency burners, generally have designs that promote better combustion stability. Mechanical air premix burners carefully mix gas and air in controlled ratios before combustion, which reduces the likelihood of flashback. Atmospheric burners rely on natural draft for air supply and operate at lower pressures, which minimizes the risk. Similarly, high-efficiency burners are designed for optimal performance and efficiency, leading to stable flames and lower flashback risks.