RH & Temperature
Organic materials expand and contract as ambient moisture levels rise and fall.
- A low RH (less than 40%) reduces chemical change but can cause materials to shrink, stiffen, crack, and become brittle.
- A sustained RH above 65% can cause adhesives in both modern (magnetic and optical media), and traditional library material to soften and lose their strength.
- In areas of poor air circulation RH should not exceed 60%; and even when air circulation is good RH should not exceed 65% in order to avoid mould growth.
- Above 70% RH and there is serious probability of mould growth.