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Rust,
mold, mildew, rot, decay, warping, stretching, lumping, caking,
agglomeration and decomposition are all common enough problems encountered
in our daily life.
It is interesting to note that the root cause of all these problems
and many more, is the presence of moisture or humidity in the air.
The storage, manufacture and transportation of material often takes
place in a humid environment which is not suited to the moisture
sensitivity of the material, leading to deterioration of stored
material, machinery, equipment and reduced product appeal.
Problems in the Pharmaceutical Industry
In the Pharmaceutical Industry, chemists have common problems of
decomposition and difficulty in compression of tablets leading to
breaking of tablets; lumping and caking of dry powders, improper
adhesion under pressure of tablets, improper drying of gelatin capsules.
The presence of high humidity in the air is the cause of all
these problems.
The rapid advance in the discovery, manufacture and use of modern
drugs has focussed attention on an infinite number of moisture control
problems. Too much moisture in the air may retard the growth of
certain organic cultures. At the very least, shelf life is particularly
shortened by the presence of humidity during the manufacturing process.
The Food Industry
Potato chips, dry breakfast cereals and soda crackers exhibit an
affinity for water when exposed to high humid conditions and will
become soggy and unappetizing.
In processing of powdery foods such as cocoas, gelatins, the sticking
or lumping of powder prevents its flow in the manufacturing process,
and this is due to high humidity conditions.
The Electronic Industry
In the electronic industry, printed wiring get corroded due to presence
of high humidity. Transistors may break down or suffer a decrease
in longevity and the uniform growth of crystals is unachievable.
The list is endless
Humidity makes for mushy transfers in the printing industry and
irregular operating of packing machines.
Seeds lose their germinating power and dry fertilizers agglomerate.
In pumping stations and high voltage rooms, expensive installations
may rust as a result of unchecked condensation.
Hence, Humidity causes waste, if left unregulated.
Air Humidity and damage caused by too High Humidity
A certain amount of water vapour is always present in the air. The
water vapour or moisture is measured in terms of relative humidity.
Normally, the actual water content in the air is lesser than the
maximum possible content that can be contained at that temperature
and pressure. The air is then said to have a certain relative humidity.
Outdoor Relative Humidity
The outdoor relative humidity is determined by the prevalent meteorological
conditions. It varies during the twenty four hour period of a day,
according to the temperature all through the year.
The picture graphically represents the plotted humidity chart for
Delhi for a year.
A relatively dry period of 40% to 50% RH is present in the summer
month April to June, whereas, during the rest of the year, humidity
keeps varying during the course of the day, often going up to 100%.
Typically in winter months, the relative humidity stands at an average
of 50% at noon, but in the mornings it is around 80%.
The outdoor relative humidity has a direct bearing on the indoor
humidity environment. The problem is compounded and distributed
as a result of infiltration through ceilings, walls and floors.
In addition to the humidity from the outside air, the humidity omitted
from people and production processes add to the overall effect as
the decisive factors in product spoilage.
How Humidity Effects Industry ?
Humidity is a constant threat to production efficiency and product
quality.
The damage which can be caused by excessive relative humidity are
principally—
– corrosion of steel and metals
– deteriorated characteristics of hygroscopic material
– increased harmful activity of micro organisms.
Corrosion: Corrosion is defined as destruction of a metal or alloy
by chemical or electrochemical reaction with its environment. In
most instances, the reaction is electrochemical in nature: a flow
of electricity between certain areas of a metal surface through
a solution capable of conducting an electric current. This electrochemical
action causes destructive alteration (eating away) of a metal at
areas.
Though corrosion is a complex function of many factors, the three
most important are—
– a voltage differential between pure and impure areas
– physical conditions of temperature and humidity
– and oxygen in the air.
Higher humidity may lead to higher condensation of water on the
metal surfaces. The concentration of molecules of water vapour increases
with increasing RH. This molecular thickness of the layers of water
eventually permits ionic conduction which accelerates the rate of
corrosion.
With iron or steel, the ferrous ion may react with hydroxyl ion
in water to form ferrous hydroxide and with oxygen to produce ferric
hydroxide (rust).
The figure shows the rate of corrosion in relatively clean and polluted
air. The critical humidity level which is at 45%, is approximately
same for clear and polluted air, however the rate of corrosion is
faster where surfaces are exposed to polluted air in combination
with high relative humidity. Industrial pollutants like sulphur
dioxide enhance the corrosion rate.
Corrosion or rusting of stored material can be seen in every Industry–Defence,
Marine, Precision parts.
Deteriorated Characteristics of Hygroscopic Materials
The figure shows the equilibrium moisture
content for some hygroscopic materials.
Certain materials require extremely low or high moisture contents
during manufacture or storage.
In the Food Industry, dry foods such as potato chips and powders
exhibit an affinity for water when exposed to relatively high humidity
conditions. Although, the product quality per se is not affected,
these foods becomes soggy and hence undesirable.
Powdered foods tend to agglomerate or lump together. The result
is that their movement through the manufacturing or packaging process
is greatly inhibited. In addition humidity may interfere with their
processing and packaging as well.
Similarly, in the Pharmaceutical Industry, chemicals and compounds
on absorbing moisture lose their medicinal value and even decompose.
Powder will not adhere properly nor lend itself to compression in
the form of tablets if the humidity is high.
In the Fertilizer Industry, dry fertilizers may agglomerate in presence
of high humidity.
Excessive Relative Humidity reduces the resistance of electrical
insulation material.
The mechanical strength of many materials like paper, deteriorates
when RH is high.
Excessive RH is deleterious to explosives.
An excessive moisture content in a material can give rise to a change
in its dimensions as e.g. in wood and plastics.
Injurious Activities of Micro Organisms
An excessive moisture content can indirectly contribute, to the
destruction of organic material by increased microbial activity.
Mold, mildew and fungi are all different types of bacteria. Outdoor
air is well endowed with this bacteria which are small enough to
be carried indoors and which will settle on materials. The spores
lie dormant until suitable conditions of temperature and humidity
are achieved. In general, the spores will not germinate below 60%
RH. The actual temperature conditions for germination may vary widely
between different types of molds.
Once germinated, the mold prospers and the speed of growth is a
function of temperature and humidity. The condensed moisture on
materials acts as a medium conducive to the growth of bacteria.
Moreover, at high temperature the activity of the microorganisms
increases but a certain amount of activity occurs even at very low
temperatures.
This microorganism growth is injurious to materials; as it not only
results in decomposition but also mechanical weakening of the products.
In most cases, bacterial growth can be arrested if RH is maintained
below 45%.
In breweries and distilleries, organic corrosion is an inherent
problem and where fungus growth on walls, hop storage, fermentation
and yeast room is unacceptable under stringent hygiene demands of
the process.
In Seed Storage, mold and fungus growth on seeds drying storage
makes them unfit for consumption and germination.
In Archival Materials, mold and mildew on stored maps, film negatives,
books or paintings in museums and libraries destroy their usefulness
and reduce their longevity.
In Chemicals and Pharmaceuticals, fungus growth on organic compounds
and medicinal substances renders them useless.
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