Ventilation is a primary measure for cargo storage by crew members. While some believe ventilation is always better than no ventilation, this isn't always true. Cargo hold ventilation is not simple; depending on the situation, there are distinctions between necessary, unnecessary, prohibited, and impossible ventilation, and even between slow (allowing for fresh air) and rapid ventilation.
To correctly understand and truly master the timing of ventilation, it's necessary to first understand the objective natural phenomenon of invisible water vapor condensing into visible water droplets (commonly known as dew, and by sailors as sweat). At a certain temperature, the water vapor content (i.e., absolute humidity, hereinafter referred to as absolute humidity) in one cubic meter of air reaches a certain level, at which point it condenses into water droplets.
In this saturated state, we call the relative humidity 100%; if the water vapor content is only half of the saturated state, the relative humidity is 50%, and so on, deduce different relative humidity levels. It's important to note that at slightly higher (or lower) temperatures, the water vapor content in the air needs to be slightly higher (or lower) to reach saturation and condense. Therefore, if a ship sets sail immediately after loading cargo at a port with very high temperature and relative humidity, and if there is no ventilation along the way and it reaches a water area with very low temperature, the water vapor in the air inside the hold is likely to condense into small water droplets on the cold hull.
