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 and 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%, below 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 | 小于 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% |