Which of the following is a critical factor in identifying leaks during air tests?

B. Soaping the joints and checking for bubbles is a critical factor in identifying leaks during air tests because it provides a visual indicator of escaping air. When a soap solution is applied to joints and fittings, any escaping air will create bubbles, making it easy to pinpoint the location of a leak. This method is straightforward and effective, allowing technicians to detect leaks without the need for complex equipment or procedures.

The other methods mentioned may not directly contribute to leak detection in the same manner. High-speed fans might help circulate air or enhance airflow, but they do not inherently reveal leaks. Increasing air pressure can help test the integrity of a system, but it might also make pinpointing a leak more difficult if no other measures are in place for detection. Submerging the tank in water is a different leakage testing method, often used in different contexts, but it is not applicable for air testing specifically. Thus, using soap to check for bubbles remains a practical and effective means for identifying leaks in air tests.