# 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
Exposure Limits | 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. | 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) | IP: NA |  | Sp.Gr: 2.5
Fl.P: NA | UEL: NA | LEL: 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
Personal Protection & Sanitation 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
Respirator Recommendations To be added later
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