Relative Humidity in Production and Process Environments
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.
| Production or Process Environment | Recommended 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% Note! 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% |
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.