NIOSH Pocket Guide to Chemical Hazards

Plaster of Paris

CAS 26499-65-0

CaSO4 • 0.5H2O

RTECS TP0700000
Synonyms & Trade Names
Calcium sulfate hemihydrate, Dried calcium sulfate, Gypsum hemihydrate, Hemihydrate gypsum [Note: Plaster of Paris is the hemihydrate form of Calcium Sulfate & Gypsum is the dihydrate form.]
DOT ID & Guide


NIOSH REL: TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)
OSHA PEL: TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)
IDLH N.D. See: IDLH INDEX Conversion
Physical Description
White or yellowish, finely divided, odorless powder.
MW: 145.2
BP: ?
MLT: 325°F (Loses H2O)
Sol(77°F): 0.3%
VP: 0 mmHg (approx)

Sp.Gr: 2.5
Fl.P: NA

Noncombustible Solid
Incompatibilities & Reactivities
Moisture, water [Note: Hygroscopic (i.e., absorbs moisture from the air). Reacts with water to form Gypsum.]
Measurement Methods
NIOSH 0500, 0600
See: NMAM or OSHA Methods
Personal Protection & Sanitation (See protection)
Skin: No recommendation
Eyes: No recommendation
Wash skin: No recommendation
Remove: No recommendation
Change: No recommendation

First Aid (See procedures)
Eye: Irrigate immediately

Breathing: Respiratory support
Swallow: Medical attention immediately
Important additional information about respirator selection
Respirator Recommendations Not available.
Exposure Routes inhalation, ingestion, skin and/or eye contact
Symptoms Irritation eyes, skin, mucous membrane, respiratory system; cough
Target Organs Eyes, skin, respiratory system
See also: INTRODUCTION   See ICSC CARD: 1217