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How Humid Can it Get

Condensation and humidity protection for transit casesWhen warm air meets a cold glass of beer, condensation forms on the surface. The resulting drips may be annoying, but they won’t ruin your beer. Should condensation occur inside a transit case, it’s another story.

Condensation and Humidity

Condensation happens when water vapor in air cools. Cooling lowers the kinetic energy of the water molecules, turning some molecules from vapor to liquid. The warmer the air, the more water vapor it contains. Thus, more condensation occurs as the temperature falls.

The amount of water in air is expressed in terms of humidity. It is reported in several ways.  But the most common terms are relative humidity and dew point. Relative humidity expresses vapor content as a percentage of the maximum that could be held at that temperature. Loosely speaking, the dew point is the temperature at which air is completely saturated, and no more moisture can be absorbed. When the temperature drops below the dew point, some moisture condenses, returning to liquid form.

Why Does it Matter?

Prolonged exposure to moist air can lead to corrosion and mold. A more immediate problem though is condensation. This can cause short-circuits, resulting in permanent damage to circuit boards and electronics.

Surprisingly, very low humidity can also be a problem. When air is exceptionally dry, electrical charges are unable to dissipate. There is an increased risk of electrostatic discharge (ESD).

How Bad Can it Be?

Defense handbook MIL-HDBK-310 offers advice on humidity for military equipment designers and identifies worst-case conditions. Low relative humidity is experienced in deserts.  For instance, 2% has been recorded at Death Valley, California. Relative humidity of 100% is quite common in high temperatures regions located near large bodies of warm water. The tropics and Persian Gulf are examples.

In terms of dew points (the temperature below which vapor condenses) 34°C is the highest recorded. Some locations, such as Belize City on the Central American coast, can see sustained periods of 30°C dew point.

Equipment Protection

Humidity will damage electronics and other delicate equipment. The way to avoid such problems is to understand the conditions your equipment will experience. An appropriately engineered transit case with seals, humidity indicators and desiccants can help you manage high humidity conditions.

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