Humidity Requirements of Materials

No single level of relative humidity provides adequate moisture content in all hygroscopic materials. Moisture content requirements vary greatly from one material to the next. We will discuss typical hygroscopic materials which require specific RH levels to avoid moisture loss and materials deterioration and/or production problems that result.

Recommended Relative Humidities
Process or Product	Temp. °C	%RH
Residences	21-22	30
Libraries & Museums
Archival	13-18	35
Art storage	16-22	50
Stuffed fur animals	4-10	50
Communication Centers
Telephone terminals	22-26	40-50
Radio & TV studios	23-26	30-40
General Commercial & Public Buildings(including cafeterias, restaurants airport terminals, office buildings & bowling centers)	21-23	20-30
Hospitals & Health Facilities
General clinical areas	22	30-60
Surgical area
Operating rooms	20-24	50-60
Recovery rooms	24	50-60
Obstetrical
Full-term nursery	24	30-60
Special care nursery	24-27	30-60
Manufacture	26	50
Ceramics
Refractory	43-66	50-90
Molding Room	27	60-70
Clay Storage	16-27	35-65
Decalcomania production	24-27	48
Decorating Room	24-27	48
Cereal
Packaging	24-27	45-50
Distilling
Storage
Grain	-14	35-40
Liquid Yeast	0-1
General manufacturing	16-24	45-60
Aging	18-22	50-60
Electrical Products
Electronics & X-ray:
Coil & transformer winding	22	15
Semi conductor assembly	20	40-50
Electrical instruments:
Manufacture & laboratory	21	50-55
Thermostat assembly	24	50-55
& calibration
Humidistat assembly	24	50-55
& calibration
Small mechanisms:
Close tolerance assembly	22	40-45
Meter assembly & test	24	60-63
Switchgear:
Fuse & cutout assembly	23	50
Capacitor winding	23	50
Paper Storage	23	50
Conductor wrapping with yarn	24	65-70
Lightning arrester assembly	20	20-40
Thermal circuit breakers
assembly & test	24	30-60
High-voltage transformer repair	26	55
Water wheel generators:
Thrust runner lapping	21	30-50
Rectifiers:
Processing selenium &	23	30-40
copper oxide plates
Fur
Storage	4-10	55-65
Gum
Manufacturing	25	33
Rolling	20	63
Stripping	22	53
Breaking	23	47
Wrapping	23	58
Leather
Drying	20-52	75
Storage, winter room temp.	10-16	40-60
Lenses (Optical)
Fusing	24	45
Grinding	27	80
Matches
Manufacture	22-23	50
Drying	21-24	60
Storage	16-17	50
Mushrooms
Spawn added	16-22	**
Growing period	10-16	80
Storage	0-2	80-85
Paint Application
Oils, paints: Paint Spraying	16-32	80
Plastics
Manufacturing areas:
Thermosetting molding
compounds	27	25-30
Cellophane wrapping	24-27	45-65
Plywood
Hot pressing (resin)	32	60
Cold pressing	32	15-25
Rubber-Dipped Goods
Cementing	27	25-30*
Dipping surgical articles	24-27	25-30*
Storage prior to manufacture	16-24	40-50*
Laboratory (ASTM Standard)	23	50*
* Dew point of air must be below evaporation temperature of solvent ** Nearly saturated
Tea
Packaging	18	65
Tobacco
Cigar & cigarette making	21-24	55-65
Softening	32	85-88
Stemming & stripping	24-29	70-75
Packing & shipping	23-24	65
Filter tobacco casing	24	75
& conditioning
Filler tobacco storage	25	70
& preparation
Wrapper tobacco storage	24	75
& conditioning
Pharmaceuticals
Powder storage (prior to mfg)	*	*
Manufactured powder storage
& packing areas	24	35
Milling room	24	35
Tablet compressing	24	35
Tablet coating room	24	35
Effervescent tablets
and powders	24	20
Hypodermic tablets	24	30
Colloids	24	30-50
Cough drops	24	40
Glandular products	24	5-10
Ampoule manufacturing	24	35-50
Gelatin capsules	24	35
Capsule Storage	24	35
Microanalysis	24	50
Biological manufacturing	24	35
Liver extracts	24	35
Serums	24	50
Animal rooms	24-27	50
Small animal rooms	24-26	50
* store in sealed plastic containers in sealed drums.
Photographic Processing
Photo studio
Dressing room	22-23	40-50
Studio (camera room)	22-23	40-50
Film darkroom	21-22	45-55
Print darkroom	21-22	45-55
Drying room	32-38	35-45
Finishing room	22-24	40-55
Storage room
b/w film & paper	22-24	40-60
color film & paper	4-10	40-50
Motion picture studio	22	40-55
Static Electricity Control
Textiles, paper, explosive control		>55
Clean Rooms & Spaces		45
Data Processing	22	45-50
Paper Processing
Finishing area	21-24	40-45
Test laboratory	23	50