What content of headspace gas samples can indicate a leak in the tank?

The presence of oxygen in headspace gas samples can indicate a leak in a tank because it suggests that air has entered the tank. Under normal conditions in a closed tank, the concentration of oxygen should remain stable and low because the tank is sealed from the outside air. If there is a leak, the oxygen from the surrounding atmosphere may infiltrate the tank, leading to an increase in oxygen levels in the headspace gas.

High levels of oxygen are of concern not only because they signal a leak but also because they can create a potentially hazardous environment, especially in tanks that store flammable materials, as increased oxygen can enhance the risk of combustion. In contrast, gases like hydrogen, nitrogen, and carbon dioxide do not necessarily indicate a leak on their own. While hydrogen can be monitored for safety reasons, its presence is not an indicator of a leak like oxygen is. Nitrogen is usually an inert gas and does not contribute to signaling leaks; similarly, carbon dioxide can be present for various reasons and does not provide direct evidence of an air seam or breach in the tank's integrity.