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.
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
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.
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.
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.