Why is humidity measured?

Our well-being and health
The indoor air quality is growing in importance as its significance to our health and to energy usage becomes more evident. A human being is best suited to, and feels best in, certain humidities and temperatures; excessively high or low humidity or temperature causes discomfort.

Over 80 % of all the diseases in towns are produced by viruses and other microorganisms which enter the body through the respiratory organs. When the relative humidity is too low, viruses live longer and can enter our lungs easily as they float in the air with the dust. In the moist lungs they are activated and generate e.g. the common cold and other illnesses. Too dry air irritates the respiratory organs and, for instance, people suffering from asthma or allergies can have breathing difficulties. Dry air also makes the skin dry.

On the other hand, mould, fungi and dust mites thrive in high humidities. Mould has become a problem  particularly in northern countries where houses are sometimes built too tight. Condensed humidity can cause mould growth on construction materials.

Health hazards are minimized when the relative humidity is kept in the range of 40...50 %RH.

Productivity
People work most efficiently when their working environment is properly air conditioned. Good indoor climate makes people feel happier at work and lowers the number of absences caused by illnesses. It has also been shown that accidents at work decrease when the working conditions have been optimized.

Processes and intrinsic safety
In many processes the correct measurement and adjustment of humidity is extremely important for the quality of products and for energy consumption. The right humidity makes it possible to optimize energy consumption and improve the end product quality and product yield.

In low humidities static electricity increases. Static electricity discharge can make some raw materials or gases in production processes explode. This is why the safety regulations in oil refineries and chemical plants, chemistry laboratories and hospitals dictate that the relative humidity is kept at an acceptable level.

Equipment
Relative humidity affects the operation of equipment. In dry conditions static electricity increases and e.g. blockages occur more often in copying machines and printers. Humidity also changes the dimensions of the paper used in copying machines or in printing. Too dry or humid conditions increase the number of faults in the operation of electrical equipment. Any water condensing inside equipment will naturally interfere with the operation of the equipment.

Storage
Most materials are hygroscopic: the amount of water they contain their water content always tries to reach a balance with the ambient relative humidity. Each material has an ideal storage humidity which should be kept up; too dry or too humid conditions can destroy the material. For example, the corrosion of iron depends directly on the air's relative humidity; corrosion starts when the relative humidity rises above 45 %RH and progresses at full speed when the humidity is over 60 %RH.