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Relative Humidity in Production and Process Environments

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Environment and indoor climate must often be within certain temperature and humidity limits to avoid deterioration and damage of products or to achieve proper process conditions.

To low relative humidity may dry up products and to high relative humidity may increase the "water activity" and the growing of mold and bacteria in process lines and their products.

  • bacteria need in general more than 90% relative humidity to grow
  • mold need in general more than 80% relative humidity to grow

The exact water activity limit for a specific organism depends on other factors such as pH, oxygen availability, the nature of the solutes present, nutrient availability and temperature. 

Recommended relative humidity for some common production and product process are indicated in the table below.

Relative Humidity in Production or Process Environments
Production or Process EnvironmentRecommended Relative Humidity
- RH -
Sugar Storage 20 - 35%
Breweries 35 - 45%
Coffee Powder 30 - 40%
Milk Powder Storage 20 - 35%
Seed Storage 35 - 45%
Unpacked Medicine 20 - 35%
Transformer Winding 15 - 30%
Semiconductors 30 - 50%
Books and Paper Archive 40 - 55%
Paper Storage 35 - 45%
Preventing Rust and Corrosion below 55%,
< 40% for no rust generation
Library 50 - 55%
Spray Paint 30 - 50%
Laboratory electronics 45 - 60%
Plastic Pallets 5 - 30%
Computer Peripherals 50 - 60%
Rust Resistance Below 40%
Medical Syrups 30 - 40%
Capsule Storage 30 - 45%
Powder Storage 30 - 45%
Wood Drying 25 - 35%
Explosives 35 - 50%
low RH may generate static electricity and spark ignitions
Normal Storage 50 - 55%
Musical Instrument 45 - 55%
Leather Product 40 - 55%
Cable Wrapping 15 - 25%
Chemical Laboratory 30 - 45%
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Related Topics

Air Conditioning Systems

Design of Air Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort.

Air Psychrometrics

Moist and humid air calculations. Psychrometric charts and Mollier diagrams. Air-condition systems temperatures, absolute and relative humidities and moisture content in air.

Ventilation Systems

Design of systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.

Related Documents

Air - Absolute Humidity

Absolute humidity is the actual mass of water vapor present in the air water vapor mixture.

Air - Drying Force

The drying force of air depends on the air moisture holding capacity and the water surface to air evaporation capacity.

Air - Humidity Ratio

The mass of water vapor present in moist air - to the mass of dry air.

Food and Foodstuff - Specific Heat

Specific heat of common food and foodstuff like apples, bass, beef, pork and many more.

Health vs. Relative Humidity

The optimum relative humidity ranges for bacteria, viruses, fungi, mites, asthma.

Indoor Relative Humidity vs. Outdoor Relative Humidity and Temperature

Recommended indoor relative humidity vs. outdoor relative humidity and temperature.

Moist Air - Psychrometric Terms

Dry and wet bulb temperature, specific volume, relative humidity,  enthalpy and more.

Moist Air - Relative Humidity

Relative humidity in moist air is the ratio of partial vapor pressure to air pressure.

Moist Air - the Mollier Diagram

The Mollier diagram is a graphic representation of the relationship between air temperature, moisture content and enthalpy - and is a basic design tool for building engineers and designers.

Saturated Salt Solutions - Controlling Air Humidity

A salt solutions can be used maintain a particular value of relative humidity.

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