California ICC UST Service Technician Practice Exam

Which gas is used for pressure testing USTs?

1. Oxygen

2. Helium

3. Carbon dioxide

4. Nitrogen

The correct answer is: Nitrogen

Using nitrogen for pressure testing underground storage tanks (USTs) is appropriate because it is an inert gas that does not react with the liquids stored in the tanks, such as fuel or oil. This quality makes nitrogen a safe choice for ensuring that any leaks can be detected without the risk of combustion or reaction with the contents of the UST. During a pressure test, nitrogen can be safely pressurized within the tank to determine if there are any leaks. If there is a drop in pressure, it indicates that there is a breach in the tank that needs to be addressed. This method is widely accepted because of nitrogen's affordability, availability, and safety profile. While other gases like helium can also be used for integrity testing, they are often more expensive and may not be as readily accessible. Oxygen is not suitable because it can create a fire hazard in a tank that has stored flammable products. Carbon dioxide, while non-flammable, does not provide the same level of sensitivity in leak detection as nitrogen due to its solubility in fuels. In summary, nitrogen is preferred for pressure testing USTs due to its inertness, safety, cost-effectiveness, and efficiency in detecting potential leaks.