What should never be used to locate gas leaks?

Using an open flame to locate gas leaks is extremely dangerous and should never be done. The presence of gas, particularly in a confined space, poses a significant explosion and fire hazard. If an open flame is introduced in an area where gas is leaking, it can ignite the gas, leading to catastrophic consequences, including injuries, fatalities, and property damage.

In contrast, the other tools mentioned, such as gas detectors, pressure gauges, and electronic sniffers, are specifically designed to identify the presence of gas safely. Gas detectors can sense various types of gas and provide alerts without posing a risk, while electronic sniffers use sensors to detect gas concentrations in the air. Pressure gauges can help assess the integrity of the gas system, but they do not pose a risk in detecting leaks. Thus, it's critical to use appropriate, safe methods and tools for leak detection to prevent hazardous situations.