Should tanks always maintain positive vapor pressure?

Maintaining positive vapor pressure in tanks is crucial for several reasons, primarily related to safety and preventing contamination. When tanks operate with positive vapor pressure, it helps to prevent the ingress of air and moisture, which can lead to dangerous situations such as flammable mixtures forming within the tank. This is particularly important in environments where volatile substances are stored, as the presence of oxygen can create a fire or explosion hazard.

Additionally, positive pressure assists in ensuring that vapors do not escape, thus minimizing the risk of environmental pollution and loss of product. It also aids in maintaining the integrity of tank systems and associated fittings by preventing the collapse of the tank under external atmospheric pressure when the vapor space is under low pressure.

While other options hint at the possibility of not maintaining positive vapor pressure, it's essential to recognize that doing so is part of standard operational safety protocols and mandatory regulations within the industry to mitigate risks associated with vapor handling.