Under what circumstance may shielding gases be mixed in their containers in the field?

In the context of welding and the use of shielding gases, mixing gases from various containers in the field poses significant safety risks. The primary reason for this is that different gases have specific properties, including how they react under certain conditions. When mixed haphazardly, there is potential for dangerous reactions or improper gas mixtures that could compromise welding quality and worker safety.

The option stating that mixing gases is never permissible aligns with industry best practices and safety standards, emphasizing the importance of using gases as specified by manufacturers and suppliers. This approach helps to ensure consistent and reliable shielding during the welding process, which is crucial for producing high-quality welds without defects.

While certain exceptions might seem reasonable — such as mixing gases when they are not available from a supplier or when employing a qualified individual to mix — these scenarios still do not mitigate the inherent risks associated with improper mixing. Therefore, the best practice is to avoid mixing gases entirely in the field, reinforcing the need for adherence to safety protocols and industry standards.