Which of the following is NOT a method by which vapor clouds can be generated?

Leak detection is primarily a process used to identify and locate leaks of hazardous substances, rather than a method that inherently generates vapor clouds. The purpose of leak detection is to ensure safety by identifying potential sources of a leak before any hazardous vapor is released into the environment, thus aiming to prevent the very formation of vapor clouds.

In contrast, the other methods listed, such as pressurized emission, sudden depressurization, and rupture of a vessel, are all processes that can lead to the sudden release of gas or vapor into the atmosphere. Pressurized emissions occur when a substance under pressure escapes through openings, leading to the formation of vapor clouds. Sudden depressurization can cause rapid expansion of gases, creating a cloud of vapor due to the cooling and condensing of the gas. Additionally, a rupture of a vessel releases the contained substance under pressure, generating a vapor cloud through a large and uncontrolled release.

Therefore, leak detection stands apart as a preventative measure, focused on identifying leaks rather than generating vapor clouds, highlighting why it is not a method by which vapor clouds can be generated.