What is a critical factor in the tank tightness testing process regarding environmental conditions?

In the tank tightness testing process, understanding thermal expansion effects is critical due to how temperature changes can impact the volume and pressure of the liquid in the underground storage tank (UST). As temperatures rise, the liquid can expand, increasing pressure within the tank, which can affect the accuracy of the tightness test results. If a tank is tested during fluctuations in temperature without taking thermal expansion into account, it could lead to false readings or misinterpretations regarding the tank's integrity.

Assessing this aspect during the testing process is essential to ensure that the results are reflective of the tank's true condition, and that no leaks are present due to the pressure variations caused by thermal effects. In contrast, while weather forecasts, soil moisture levels, and gas prices are relevant to the overall operational management of USTs, they do not directly influence the technical processes involved in tightness testing like thermal expansion does.